Booklet Topic2 StudyGuide - Chemistry Teaching Resources€¦ · y - n Challenge Chemistry.I.S.E ge...
Transcript of Booklet Topic2 StudyGuide - Chemistry Teaching Resources€¦ · y - n Challenge Chemistry.I.S.E ge...
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 44
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 1
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Higher Chem
istry
Topic 2:
Reaction Rates
1. C
oncentration and Collisions
2. Particle Size and C
ollisions3.
Temperature and C
ollisions
C
heck Test
H
ome Practice
2.1CollisionTheory
1. C
atalytic Converters
2. H
eterogeneous Catalysts
3. H
omogeneous C
atalysts
C
heck Test
H
ome Practice
2.2CatalystsAt W
ork
1. C
onsidering the Investigation
2. The Experim
ental Work
3. Processing the R
esults
C
heck Test
H
ome Practice
2.3ConcentrationAnd Rate
1. C
onsidering the Investigation
2. The Experim
ental Work
3. Processing the R
esults
C
heck Test
H
ome Practice
2.4Tem
peratureAnd Rate
1. Progreass of a R
eaction
2. C
alculating the Rate
3. C
omparing R
eaction Progress
C
heck Test
H
ome Practice
2.5ReactionProgress
1. Energy D
uring Collision
2. Potential Energy D
iagrams
3. C
atalytic Effect
C
heck Test
H
ome Practice
2.6ActivationEnergy
1. D
istribution Graphs
2. C
oncentration and Temperature
3. C
atalytic Effect
C
heck Test
H
ome Practice
2.7EnergyD
istribution
C
onsolidation A
C
onsolidation B
C
onsolidation C
C
onsolidation D
ConsolidationW
ork
LessonActivities
Study Guide
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istry © R.I.S.EPage 2
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
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munity - based on Challenge Chem
istry © R.I.S.EPage 43
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
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munity - based on Challenge Chem
istry © R.I.S.EPage 42
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Consolidation
DQ1.
The reaction between oxalic acid and acidified potassium
permanganate solutions
can be used to study the effect of tem
perature on reaction rate.
2 (aq) + 6 H+(aq)
4 -(aq) 2+(aq) + 10 CO
2 (aq) + 8 H
2 O2 (l)
a)
1
b) -1
1
c) Suggest why it is diffi
cult to obtain an accurate reaction time at
1
Q2. H
ydrogen gas can react with bromine gas to form
hydrogen bromide gas.
H2 (g) + Br2 (g)
2 HBr (g)
a)
One step in this reaction is the form
ation of an activated complex.
i) Explain what is m
eant by the term ‘activated com
plex’.
1
ii) D
raw a diagram of the activated com
plex formed in this reaction.
1
b)
Increasing the temperature of the reaction m
ixture increases the reaction
rate. O
ne reason for this is that it increases the frequency of collisions
between the reactant m
olecules.
i)
increasing tem
perature?
1
ii)
How does tem
perature relate to the energy of the molecules?
1
Q3.
solution and hydrogen gas.
Zn
(s) + 2 HCl (aq)
ZnCl2 (aq) + H2 (g)
Experim
ent A used 10 cm
3 of 2 moll -1 acid
and the volum
e of hydrogen gas produced was
stopped there was still plenty of zinc left.
Th
e graph shows the total volume of hydrogen
collected as the reaction progressed.
a)
How, precisely, would the initial rate of reaction have com
pared if
1 m
oll -1 acid had been used?
1
b) Copy the graph shown and add a solid line labelled B to show the volum
e
of hydrogen collecting if 10 cm
3 of 1 moll -1 acid had been used.
1
c) C, to show the reaction progress if an equal
mass of zinc powder had been used with 10 cm
3 of 2 moll -1 acid.
1
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uide - Reaction Rates
Collision Theory
2.1
⊙��
IntroductionTh
e rate of a chemical reaction can be affected by catalysts, the
concentration and temperature of the reactants, and the size of
particle in the case of a solid. But why should this be? Th
is whole section is about understanding in more detail why catalysts, concentration,
temperature and particle size affect the rate of chem
ical reactions.O
ne clue is that most chem
ical reactions involve at least one reactant which is a gas, a liquid, or in solution. In other words, they involve atom
s, molecules, or ions that are m
oving and so are able to collide with the other reactant. Th
e idea of reactions taking place by the reactant particles colliding with each other is called the ‘collision theory’ of reactions. Th
e first lesson topic looks at how the effects of concentration, particle size, and temperature
on the reaction rates can be explained in terms of collisions between reactant particles.
{��
Concentration And CollisionsTh
is activity looks at how collision theory can explain why the concentration of reactantsaffects the rate of a chem
ical reaction.Collision theory can be thought of as sim
ply comm
on sense. Firstly, for a reaction to occurthe particles of the two reactants have to m
ake contact. In other words, they must collide.
Secondly, the reactant particles have to collide with enough force to break the existing bondsin their particles. G
entle collisions just result in reactant particles bouncing apart unchanged.Breaking bonds requires energy and that energy com
es the force of the collision.Th
irdly, the reactant particles may also have to collide in such a way that specific parts of each
molecule com
e into contact. This is called the Collision Geom
etry.
Collision theory states that substances can only react with each other if (i) their
particles collide with each other, (ii) the collisions have enough energy and (iii) they
collide with the correct collision geom
etry.Consider the reaction of hydrochloric acid with a piece of m
arble. Both of these compounds are
ionic so the reactant particles are actually ions in this case. The m
arble is solid, so its ions are fixed. Th
ey are not moving about. Th
e hydrochloric acid is a solution, so its ions are moving about in all
directions all the time. Th
e acid ions are continually colliding with water molecules, the sides of the
beaker, and the piece of marble, but a chem
ical change only takes place when an acid ion collides with a m
arble ion.
Note: The ion particles in
these diagram
s are
not drawn to scale;
they are millions of
tim
es too large
compared with the
beaker size.
W
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igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
|���Particle Size And Collisions
This activity looks at how collision theory can explain why the particle size of a solid reactant
affects the rate of a chemical reaction.
In this situation the word particle is referring to lumps, grains, and fine dust (all of which are
made of m
illions of even tinier particles, i.e. atoms, m
olecules, or ions).Consider again the reaction of hydrochloric acid with m
arble. In both diagrams the
concentration of acid ions is the same and the total m
ass of marble is also identical. Th
e onlydifference is the particle size (i.e. the size of the bits) of the m
arble.
Think about the two diagram
s on the previous page.
with m
arble ions?
happen before an acid ion can react with a marble ion?)
Think about the two diagram
s above.
greater area of surface exposed for reaction?
(i.e. a greater frequency of collisions)?
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uide - Reaction Rates
Consolidation
CQ1.
The relative rate of a chem
ical reaction was measured at different tem
peratures.
a)
Using graph paper, plot a graph of the relative rate against temperature.
2
b)
Use your graph to calculate the temperature increase required to increase
the relative rate from 0.030 to 0.060 s -1.
1
Q2.
phosphorus oxide. Powdered phosphorus of the same total m
ass reacts faster
than the lump.
a)
Explain this effect in terms of collision theory.
1
b)
energy for this reaction?
1
Q3. H
ydrogen peroxide reacts with iodide ions under acidic conditions to produce
water and iodine.
H
2 O2 (aq) + 2 I —
(aq) + 2 H+(aq)
2 H2 O
(l) + I2 (aq)
of the iodine. Th
is system can be used to m
easure the effect on the reaction
rate of changing the concentration of iodide ions
a) 1
b)
Describe how the reaction can be tim
ed.
1
c) D
escribe how the relative rate is calculated from the reaction tim
e.
1
Q4. Th
e following table gives information about two catalytic processes. Copy and
com
plete the table.
H
2 O2 (aq) + 2 I —
(aq) + 2 H+(aq)
2 H2 O
(l) + I2 (aq)
2
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uide - Reaction Rates
Consolidation
BQ1.
If a motorist m
istakenly uses the old-style leaded petrol in a car that has a
catalytic converter then the catalyst will be ‘poisoned’ by the lead.
a) Explain what is m
eant by poisoning the catalyst.
1
b)
Exhaust gases react when they pass through a solid network of the catalyst.?
1
Q2. Urea is a substance found in hum
an urine.
The enzym
e urease catalyses the breakdown
of urea into carbon dioxide and amm
onia.
NH
2 CON
H2 + H
2 O
CO2 + 2N
H3
Th
e graph shows the potential energy diagram
for this reaction (per m
ole of urea).
a)
Calculate the activation energy for this reaction.
1
b)
and add a dotted line to show the progress when acid is the catalyst.
1
c)
Give another exam
ple of an enzyme-catalysed reaction.
1
Q3. Th
e graph below shows the volume of carbon dioxide given off during the
reaction of calcium
carbonate with 1 mo1 l -1 hydrochloric acid.
a)
Calculate the average rate of reaction over the first 20 minutes.
2
b) Calculate the value of the average rate of reaction for the tim
e interval
between 80 and 100 m
inutes.
1
c) Explain why these two rates of reaction are different.
1
d) Suggest why the graph has levelled off at 140 m
inutes.
1
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uide - Reaction Rates
}����Tem
perature And CollisionsTh
is activity looks at how collision theory can explain why the temperature of the reactants
affects the rate of a chemical reaction.
Increasing the temperature causes the reactant particles to m
ove faster. This m
eans that theycollide m
ore often and also that they collide with greater kinetic energy (movem
ent energy).Both of these effects will cause a faster reaction, but it is m
ainly the increase in kinetic energythat m
akes a small increase in tem
perature have such a dramatic effect. Just an increase of
10 °C is often sufficient to double the rate of a reaction.
In the case of hydrochloric acid reacting with marble, an increase in tem
perature affects the acid ions considerably since they are free to m
ove about in the solution. The m
arble ions also vibrate m
ore in the solid but they are still unable to move around.
In both diagrams the concentration of acid ions is the sam
e and the mass and particle size of the
marble is identical. Th
e only significant difference is the speed at which the acid ions are moving.
Think about the two diagram
s above.
reaction?
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igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Check Test
2.1
Q1. The rate of a chem
ical reaction depends
A on both the frequency and energy of
the collisions between reactant particles.
B only on the speed of the colliding
reactant particles.
C only on the energy of the collisions
between reactant particles.
D
only on the frequency of collisions
Q2. Increasing the concentration of a reactant
leads to a faster reaction rate because the
A particles m
ove around less.
B energy of the collisions increases.
C particles travel faster.
D
frequency of collisions increases.
Q3. Breaking up a single lump into sm
aller
pieces causes
A
an increase in the energy of its surface
atom
s.
B an increase in its surface area.
C a decrease in the energy of its surface
atom
s.
D
a decrease in its surface area.
Q4. Compared with a single lum
p, an equal
mass of a powdered solid reacts faster
because
A
a powder has more kinetic energy.
B the energy of collisions is greater.
C m
ore collisions per second are possible.
D
a powder acts as a catalyst.
Q5. Increasing the temperature of a reactant
causes its particles to
A m
ove slower with higher kinetic energy.
B m
ove faster with higher kinetic energy.
C m
ove slower with lower kinetic energy.
D
move faster with lower kinetic energy.
Q6. How is the effect of increased tem
perature
on reaction rate best explained?
A O
nly the frequency of collisions
between reactant particles is increased.
B O
nly the speed of the colliding
reactant particles is increased.
C O
nly the energy of collisions
between reactant particles is increased.
D
Both the frequency and the energy of
collisions between reactant particles are
increased.
Q7.
energy of collisions in the reaction between
a solid and a solution?
A Increasing the tem
perature of the
solution
B Using a solution of greater concentration
C Crushing the solid into a fine powder.
D
Using larger pieces of solid totalling the
sam
e mass
Q8.not increase
the frequency of collisions in the reaction
between a solid and a solution?
A Increasing the tem
perature of the
solution
B Using a solution of greater concentration
C Crushing the solid into a fine powder.
D
Using larger pieces of solid totalling the
sam
e mass
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Consolidation
AQ1.
(s) + 2 H
+(aq) 2+(aq)
+ H
2(g)
Explain in term
s of collision theory why increasing the concentration of the acid
ions speeds up the chemical reaction.
1
Q2. Th
e rate of a chemical reaction
between two types of m
olecule
depends on the kinetic energies
of their collisions.
The graph shows the distribution
of collisions with particular
kinetic energies. E
a represents
the activation energy for the
reaction
a)
unsuccessful collisions (i.e. collisions that would not result in reaction).
1
b)
if the tem
perature is increased by about 10 °C.
1
c) Explain in term
s of the distribution graph how a catalyst increases the rate
of the reaction
1
Q3. O
ne of the processes used to manufacture petrol is the catalytic cracking of the
heavy fractions obtained from
crude oil. During this process the catalyst
becom
es coated in carbon which reduces the efficiency of the catalyst.
a)
Describe how the carbon is rem
oved from the catalyst.
1
b)
1
Q4. Th
e reaction between hydrochloric acid and sodium thiosulphate produces a
cloudy precipitate of sulfur.
2 HCl(aq) + N
a2 S
2 O3(aq)
2 NaCl + S
(s) + SO2(g) + H
2 O(l)
Th
e time taken for this precipitate to obscure a cross on a piece of paper beneath
the beaker can be used to investigate the relationship between concentration
and rate of reaction.
a)
Calculate the relative rate for each result (including the correct unit).
2
b) Use graph paper to plot a graph of relative rate against concentration.
2
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uide - Reaction Rates
Home Practice
2.7
Q1. D
istribution graphs
can be drawn to aid
the understanding
of reaction rates.
a)
highest kinetic energy?
1
b)
kinetic energy value to the left of Ea not result in a reaction?
1
c)
Describe what the shaded area represents.
1
Q2. Changing experim
ental
conditions can change
the energy distribution
graph. This graph shows
the effect of changing
the concentration of a
reactant.
a)
1 or C2 ?
1
b) Sketch a sim
ilar graph to show the energy distribution at
tem
perature, T 1, and use a dotted line to show the energy
distribution at a slightly higher tem
perature, T2 .
2
c) Explain, by referring to your graph, why a m
oderate
increase in tem
perature can have a dramatic effect on the
reaction rate.
2
Q3. 2
Total (10)
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uide - Reaction Rates
Home Practice
2.1
Q1. l -l
a)
the temperature of the acid is changed to 40 °C?
1
b) l -l)?
1
Q2. Th
e reaction of zinc with sulphuric acid can be explained
in terms of hydrogen ions reacting with zinc atom
s.
a)
In terms of collision theory, explain why an equal m
ass of
powdered zinc will react faster than a single piece.
1
b) i)
num
ber of collisions per second?
1
ii) Explain why this changes the rate of reaction.
1
c) i)
energy of collision of the reactant particles?
1
ii)
Explain why this changes the rate of reaction.
1
Q3. Th
e diagram shows two
equal-sized pieces of
m
agnesium about to be
dropped into acids of
different concentration.
a)
In which tube will the reaction be faster?
1
b) Explain your answer in term
s of collision theory.
1
Total (10)
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uide - Reaction Rates
Catalysts At Work
2.2
⊙��
Introduction
money and som
etimes m
ake some otherwise im
possible reactions actually happen. How is
This lesson topic considers catalysts at work in different kinds of chem
ical reaction.
{��
Catalytic Converters
This activity looks at how the catalytic converter in a car exhaust system
converts pollutinggases into non-polluting substances.Th
e converter has two sections. In the first section, platinum and rhodium
act as catalysts.Th
ey convert oxides of nitrogen (e.g. NO
and NO
2 ) into ordinary nitrogen and oxygen. In
from a sm
all air intake, they convert poisonous carbon monoxide into the safer carbon dioxide.
The gas m
olecules collide with the catalyst and stick to its surface. This is called adsorption.
The reactant gas m
olecules form weak bonds with the catalyst atom
s and this in turn weakensthe bonds within the reactant m
olecules making them
more reactive toward each other.
molecules, the weak bonds with the catalyst break and
the product molecules depart. Th
e surface of the catalyst is then available to adsorb m
ore reactant molecules and
repeat the process over and over again.
Catalytic converters can only be used in the exhaust systems of cars that run on unleaded petrol.
so prevent the adsorption of the pollutant molecules. Th
is reduces the surface activity of the catalyst and m
ay even render it completely useless. Th
is effect is known as poisoning the catalyst.
Think about the use of catalysts in a car exhaust system
.
car exhausts?
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Self Check
2.7
Q1. The diagram
shows a distribution graph.
Th
e graph has this shape because molecules
at a particular tem
perature
A all have the sam
e speed.
B differ in direction of movem
ent.
C all have the same kinetic energy.
D
differ in kinetic energy.
Q2.
A average kinetic energy of the m
olecules to
the left of E
a on a distribution graph.
B the minim
um kinetic energy of collision
for colliding molecules to react.
C average kinetic energy of the m
olecules to
the right of E
a on a distribution graph.
D the m
aximum
kinetic energy of collision
for colliding m
olecules to react.
Q3.
reactions because the light energy
A is reflected by som
e molecules.
B is absorbed by som
e molecules.
C increases the activation energy.
D
increases the concentration of the
m
olecules.
Q4. The tem
perature of a substance is a measure
of the
A
average kinetic energy of its particles.
B number of particles in a substance.
C highest kinetic energy of its particles.
D
concentration of particles in a substance.
Questions 5 to 7 refer to the following
distribution diagrams
Q5.
increasing the temperature?
Q6.
increasing the concentration?
Q7.
adding a catalyst?
Q8. To increase the rate of a reaction, it is
necessary to increase the
A area under the distribution curve before
Ea .
B position of E
a on the distribution curve.
C area under the distribution curve beyond
E
a .
D total area under the distribution curve.
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The total area under the graph also has to be sam
e since the number of m
olecules is still the same.
This m
eans that the height of the graph becomes lower as the spread to the right takes place. Th
e
}���Catalytic Effect
can have a major effect on the reaction rate.
This activity explains the effect of a catalyst in term
s of activation energy.
If the same concentration of m
olecules at the same tem
perature is used in an uncatalysed anda catalysed reaction, then the energy distribution graphs will be identical in shape and size.H
owever, the activation energy is not the same. Th
e catalysed reaction has a lower activationenergy. Th
is means that a larger portion of the distribution lies to the right of the E
a (catalysed).
Think about the effect of increasing tem
perature.
in the rate of reaction?
Think about the energy distribution graphs shown for an uncatalysed and
a catalysed reaction.
a to shift?
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|���H
eterogeneous CatalysisIn the catalytic converter in the car exhaust system
the reactants are in the gas state and the
catalysis is referred to as heterogeneous catalysis. Th
is activity is about examples of heterogeneous catalysis.
In heterogeneous catalysis the catalyst is in a different state from the reactants.
( ‘hetero’ = different, ‘geneous’ = kinds)Th
e following experiment was probably used last year to show heterogeneous catalysis in action. It
involves the reaction of amm
onia gas with oxygen gas using platinum as the catalyst.
Th
e apparatus would be set up as shown
Th
e platinum wire is heated until it just
glows red.
It is then held just above the concentrated
am
monia solution in the flask.
Th
e wire is seen to glow even hotter and
eventually brown fumes m
ay be seen.
The above reaction is the basis of the O
stwald process for the industrial manufacture of nitric acid.
Other industrial processes com
monly involve heterogeneous catalysis. Th
e Haber process uses iron
as the catalyst in manufacturing am
monia from
nitrogen gas and hydrogen gas. Th
e process of hydrogenation is carried out in the manufacture of m
argarine from vegetable oils
and hydrogen gas using nickel as the catalyst. In the Contact process for the manufacture of
sulphuric acid, sulfur dioxide is reacted with oxygen in the presence of vanadium pentoxide as the
catalyst.Poisoning of catalysts happens in industrial processes too. Th
is can be caused by impurities in the
reactants or by pollutants in the products.
Think about this reaction.
W
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uide - Reaction Rates
}���H
omogeneous Catalysis
Quite often, catalysts will be in the sam
e state as the reactant molecules. Th
is type of catalysis is known as hom
ogeneous catalysis.Th
is activity looks at examples of catalysis when the reactants and the catalyst are all in the
same state, usually that of solution.
In homogeneous catalysis the catalyst is in the sam
e state from the reactants.
( ‘homo’ = sam
e ‘geneous’ = kinds)Th
e following experiment was probably used last year to show hom
ogeneous catalysis in action. Cobalt chloride is used as a catalyst to speed up the reaction between hydrogen peroxide and Rochelle salt. Th
e reaction produces bubbles of carbon dioxide and oxygen.
pink Co2+
green Co3+
pink Co
2+
In ordinary life, many reactions in the solutions in your body cells are catalysed by natural
catalysts known as enzymes.
Enzymes are biological catalysts. Th
ey are complex protein m
olecules
which speed up specific chem
ical changes by homogeneous catalysis.
Enzymes are also used in industry. For exam
ple, in the confectionery industry invertase catalyses the breakdown of ordinary sugar into glucose and fructose. Invertase is one of several enzym
es found in yeast. Yeast fungi also produce enzym
es that convert sugar found in grapes into wine. The
brewing industry too depends on yeast to convert sugars from grain into the alcohol and carbon
on enzymes produced inside
certain bacteria to convert lactose in milk into lactic acid, an im
portant step in making yoghurt.
Think about this reaction.
For example, in the petrochem
ical industry large oil molecules are cracked to form
smaller m
ore useful m
olecules such as ethene using aluminosilicate powder as the catalyst. H
owever, the reaction also produces carbon powder (soot) which coats the catalyst. So the catalyst powder is
continually rem
oved to have the soot burned off and then returned for
further use. Th
is renewing of the catalyst after poisoning is known as
regeneration.
WW
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
|���Concentration And Tem
peratureTo increase the rate of a reaction m
ore collisions require to have an energy greater than theactivation energy. In term
s of distribution graphs, this means increasing the shaded area to the
right of Ea along the kinetic energy axis.
Increasing either the concentration or the temperature will do this, but in quite different ways.
This activity looks at how increasing the concentration or increasing the tem
perature affects an energy distribution graph.
In the case of concentration, an increase simply increases all values across the distribution.
For example, doubling the concentration doubles the height of the graph at all positions.
Activation energy is the minim
um kinetic energy of collision needed for a chem
ical
change to potentially take place
The rates of som
e reactions can be increased by light as the light energy can be absorbed by the m
olecules to increase their energy and provide a greater number of collisions with energy greater
than the activation energy.
W
Think about the effect of increasing the concentration.
shaded area?
In the case of temperature, an increase causes the m
olecules to move faster and therefore have
increased kinetic energy. In fact, the temperature of a substance is a m
easure of the average kinetic energy of its particles.
The effect on the distribution graph is to spread it out to higher values of kinetic energy. Th
ere will still be som
e slow-moving m
olecules, so the left side of the graph still starts at zero kinetic energy.
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
ENERGY DISTRIBUTION
2.7
⊙��
Introduction
This m
eans that their kinetic energies also differ. In any given sample, the m
olecules have a range of kinetic energies. Th
is range is known as an energy distribution.
This lesson looks at the effect of a distribution of kinetic energies on the rate of a reaction.
{��
Distribution Graphs
This activity looks at distribution graphs for kinetic
energies.
This graph shows how kinetic energy is distributed
among m
o1ecules. Some m
olecules always have ahigher kinetic energy than the m
ajority and some a
the energy of collision must be equal to, or greater than, the activation energy.
The point along the x-axis at which the kinetic energy
equals the activation energy is labelled Ea on thegraph. O
nly those collisions with greater kineticenergy (i.e. to the right of Ea on the graph) haveenough energy to react. Th
eir total is represented bythe shaded area. Th
e greater this number (i.e. the
greater the shaded area), the faster the reaction.
Think about the distribution graph with E
a marked on it.
a just a point along the x-axis?
a not result in reaction?
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Self Check
2.2
Q1. Catalytic converters are fitted to cars to
A allow the exhaust gases to cool faster.
B rem
ove pollutant gases from the
exhaust.
C accelerate the m
otion of the car.
D
increase the rate of petrol burning.
Q2.
catalyst when it
A breaks free from
the surface of the
catalyst as a product of the reaction.
B starts to react with another m
olecule on
the surface of the catalyst.
C passes underneath the surface of the
catalyst.
D
becomes weakly bonded to the surface
of the catalyst.
Q3.
A the reactants used are toxic gases.
B its surface is blocked by an im
purity.
C it is heated to too high a tem
perature.
D
its surface is fully occupied by reactant
m
olecules.
Q4. Cars with catalytic converters have to use
lead-free petrol to avoid the catalyst
A cooling down too m
uch.
B becom
ing poisoned.
C heating up too m
uch.
D
corroding away.
Q5. In heterogeneous catalysis the catalyst
must be
A
in a different state from the reactants.
B an enzym
e.
C in the sam
e state as the reactants
D
a transition metal.
Q6. Regenerating a catalyst means
A
using it again in scrap metal.
B m
elting it down and letting it
recrystallise.
C getting rid of im
purities on the surface.
D
making m
ore of it from a biological
source.
Q7. In homogeneous catalysis the catalyst m
ust
be
A in a different state from
the reactants
B in a different state from
the products
C in the sam
e state as the reactants.
D
in the same state as the products
Q8.not true of
enzym
es?
A Th
ey catalyse reactions in living
organism
s.
B They are used in industrial processes.
C Th
ey are biological catalysts.
D Th
ey are simple carbohydrate m
olecules.
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munity - based on Challenge Chem
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Home Practice
2.2
Q1. Catalytic converters are found in car exhausts and are used to convert
carbon m
onoxide and nitrogen dioxide into non-polluting gases.
a)
in such catalytic converters.
2
b)
unleaded petrol?
1
Q2. Com
plete the paragraph below using words from this box.
more
strengthens
break
weak
adsorption
less
weakens
make
strong condensation
Reactant molecules collide with the catalyst and stick to the surface.
This is called ... (a) .... Th
e reactant molecules form
... (b) ... bonds
with the catalyst and this in turn ... (c) ... the bonds within the reactant
molecules m
aking them ... (d)
bonding changes to that of the product molecules, the weak bonds with
the catalyst ... (e) ... and the product molecules depart. Th
e surface of
the catalyst is then available to adsorb ... (f) ... reactant m
olecules.
3
Q3. 1
Q4. Com
plete the following table with the name of the catalyst used
for each process and the type of catalysis involved.
Reaction
Catalyst
Type of Catalysis
a)
Haber Process
i)
ii)
b) O
stwald Process
i)
ii)
b)
Fermentation
i)
ii)
3
Total (10)
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munity - based on Challenge Chem
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Home Practice
2.6
Q1.
a) D
raw a graph to show how the potential energy of two colliding
m
olecules changes during an endothermic reaction .
You should label the axes and the potential energies for the
reactant and product m
olecules.
3
b) Indicate clearly on your diagram
the activation energy for
the reaction?
1
c)
Draw a dotted line on your graph to show how the potential
energy might change as the reaction proceeds in the presence
of a catalyst.
1
Q2. Th
e activation energy is an important m
easure for any reaction.
Give the sym
bol used for activation energy and the units it
is measured in.
1
Q3. D
uring the progress of the reaction
between molecules an activated
com
plex can be formed.
a)
Illustrate, using the above two molecules, what an activated
complex m
ay look like.
1
b)
Explain what your diagram shows?
1
c)
is form
ing?
1
d)
In terms of energy, what happens when the products are
formed from
the activated complex?
1
Total (10)
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igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Self Check
2.6
Q1. The graph shows the potential energy as
two m
olecules react with each other.
Point X on the graph is when the
A
reactant molecules are m
oving at their
fastest.
B reactant m
olecules are at the point of
m
aximum
collision.
C product molecules are m
oving at their
fastest.
D
product molecules have separated but
not yet slowed down.
Q2.
potential energy diagram?
Q3.
A an unstable arrangem
ent of atoms form
ed
at the m
aximum
of the PE barrier.
B a stable arrangement of atom
s formed at
the maxim
um of the PE barrier.
C an unstable arrangem
ent of atoms form
ed
at the lowest point of the PE graph.
D
a stable arrangement of atom
s formed at
the lowest point of the PE graph.
Q4.
potential energy needed to
A m
ake chemical bonds active.
B cause reactant m
olecules to collide.
C form an activated com
plex.
D produce the product m
olecules.
Q5.
this example?
the tim
e interval 2 - 4 minutes?
A
10 kJ m
ol -1
B
20 kJ mol -1
C
30 kJ mol -1
D
40 kJ m
ol -1
Q6. The effect of a catalyst on an energy
pathway is to
A
increase the potential energy of the
products.
B increase the activation energy.
C decrease the potential energy of the
products.
D
decrease the activation energy.
Q7. In which potential energy diagram does the
dotted pathway show the effect of a catalyst?
Q8.
the activated complex form
ed?
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Concentration and Rate
2.3⊙��
IntroductionTh
ough no longer Prescribed Practicals, the next two sheets will give you the opportunity to becom
e familiar with the calculation of Relative Rates and practice in writing Investigation Reports.
Th
e purpose of this lesson topic is to investigate in more detail the way
that the concentration of a reactant affects the rate of a chem
ical reaction.
{��
Considering The Investigation
The aim
of this experiment is to find the effect of varying the concentration of iodide ions on
the rate of reaction between hydrogen peroxide and an acidified solution of potassium iodide.
There is no need to understand the full detail of this reaction. You only need to know that it
produces iodine which gives an intense blue/black colour when starch is present.
hydrogen +
iodide +
hydrogen
water + iodine
peroxide
ions
ions
m
olecules(colourless)
(colourless)
(colourless)
(blue/black with starch)
To measure the rate of reaction you need to be able to tim
e the reaction from its start to som
edefinite and obvious point later in the reaction.In this case, this is achieved by having a little thiosulphate in the reaction m
ixture. The thiosulphate
uses up the iodine before the blue/black colour can form. O
nly when all the thiosulphate has gone does the blue/black colour appear.
be varied. The concentrations and volum
es of the other chemicals involved will be kept constant as
will the temperature at which the experim
ents are performed.
Since the number of m
oles of thiosulphate ions present will be the same in each experim
ent, the appearance of the blue/black colour will always represent the sam
e extent of reaction.
So if t is the time it takes for the blue/black colour to appear then 1/t
gives a measure of the
relative rate of reaction.
relative rate = 1/t
when t is in seconds (s), the unit for relative rate is 1/seconds or s -1
Think about how the investigation m
ight be carried out.
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munity - based on Challenge Chem
istry © R.I.S.EPage 14
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
|���Th
e Experimental W
orkTh
is investigation should take about 40 minutes to com
plete. If you have insufficient tim
e tocom
plete it in this lesson ask your teacher’s advice as to what to do next.In this activity, a table of results is produced for a series of short experim
ents using a differentconcentration of iodide ions each tim
e.
Hazards:
Eye protection should be worn as sulphuric acid and
hydrogen peroxide can irritate eyes.
1. Collect as m
any 100 cm3
(best size of m
easuring cylinder or even a pipette) the required
volumes for each m
ixture as shown in the table below.
For your raw results you need simply record the volum
e of potassium iodide used and the tim
e taken for the blue colour to appear.
3. Take the first beaker or flask and place on a white surface.
3 of hydrogen peroxide solution and start timer.
stop the tim
er when the blue colour first appears. Record the
reaction time, t.
6. Repeat the experim
ent for each of the mixtures.
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munity - based on Challenge Chem
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
}���Catalytic Effect
This activity explains the effect of a catalyst in term
s of activation energy.
reaction pathway,so it involves different collisions in a series ofsteps which give the sam
e products at the end.Th
e collisions in the catalysed route require less kinetic energy for them
to be effective in producing the change. But why should this be?It is because the activation energy for each collision step in the catalysed route is m
uch lower than in the uncatalysed route. It is a bit like the difference between clim
bing right over the sum
mit of a high
mountain or taking a route round the
side over a series of much lower hills.
This can be seen in the potential energy diagram
which shows both the uncatalysed route(solid line) and catalysed route (dotted line).Th
e shapes of these graphs can vary enormously depending on all the different collision steps to get
from reactants to products. H
owever, the highest energy barrier (activation energy) on the catalysed route will always be lower than the highest energy barrier (activation energy) on the uncatalysed route.Th
ink about the potential energy diagram above.
potential energy of the reactants?
potential energy of the products?
activation energy?
to form
an activated complex?
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 30
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
|���Potential Energy D
iagrams
This activity looks further at potential energy diagram
s for chemical changes.
potential energy diagram is known as the activation
energy. It is usually represented by the symbol E
a .Th
e mom
entary arrangement of atom
s at them
aximum
point of the energy pathway is known asthe ‘activated com
plex’. The potential energy
diagram opposite sum
marises these points.
An Activated complex is the unstable arrangem
ent of atoms form
ed at the
m
aximum
of the potential energy barrier.
Activation energy is the additional potential energy which has to be achieved
by colliding m
olecules to form an activated com
plex.
E
a =
PE (activated complex)
— PE (reactants)
Values for activation energy are usually in kilojoules per m
ole ( kJ mol -1)
Potential Energy Graphs sim
ilar to those below are available in your Notes.
a on each example and
calculate its value.
In reality, it is impossible to m
easuredirectly actual values for PE as shown in these Graphs. Instead we rely on m
easurements of energy changes to deduce likely values.
Think about the potential energy graph for two m
olecules reacting.
the energy pathway has been reached?
downwards after the point of full collision?
the reacting m
olecules?
WW
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 15
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
}���Processing the Raw Results
The purpose of this activity is to exam
ine the results by constructing a graph of the relativerate plotted against the relative concentration of iodide ions.
3, the concentration of iodide ions in each experim
ent is directly proportional to the volume of potassium
iodide solution used. 3 of 0.1 m
oll -13 of the m
ixture gives aconcentration which is one tenth of the original, i.e. 0.01 m
oll -1. 10 cm3 would be double this at
0.02 mol l -1 and so on.
relative concentrations. Quite often we will opt for the latter (easier)
option and use the volumes directly.
1. Calculate the relative rate for each experim
ent.
2.
On the graph provided in your notes, label the axes and decide
on a suitable scale for each axis.
3. Rem
ember to include the appropriate units for each axis.
4. Plot the points for the experim
ent and draw a ‘line of best fit’.
Think about the graph you have drawn.
or in som
e other way?
this investigation?
Think about the investigation you have just com
pleted.
Reliable?Precision? In what ways could you
have been m
ore precise?
Accuracy of any of your
measurem
ents? (Better equipment available?)
It is important, at the end of an Investigation, to reflect and evaluate your procedures.
KHS June 2014 - Cheviot Learning Com
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istry © R.I.S.EPage 16
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Self Check
2.3
Q1. To examine the effect of concentration
on the rate of reaction, it is necessary to
A
vary the concentrations of all the
reactants and keep the tem
perature
constant.
B keep the tem
perature constant and vary
the concentration of just one reactant.
C vary the concentration of one reactant
and change the temperature each tim
e.
D
keep the concentrations of all the
reactants constant and vary the
temperature.
Q2. Starch solution is added to the reaction
m
ixture in order to detect when
A iodine just begins to be used up.
B the reaction ends.
C iodine is no longer used up.
D
the reaction starts.
Q3. The reaction is tim
ed from
A when the blue/black colour disappears
until the reaction ends.
B the start until the blue/black colour
disappears.
C when a blue/black colour appears until
the reaction ends..
D
the start until a blue/black colour
appears.
Q4.
unimportant?
A
Size of beaker/flask used for the reaction
B Concentration of iodide ions
C Volum
e of hydrogen peroxide
D
Temperature of the Reactants
Q5. If t is the time taken, which expression is
used to calculate the relative rate?
A
1 / t 2
B
1 - t 2
C
1 / t
D
1 - t
Q6.
A
s -2
B
s -1
C
s 2
D
s
Q7.
varies with concentration?
Q8.
increased, the rate of reaction will
A increase m
ore and more rapidly.
B rem
ain constant.
C decrease gradually.
D increase steadily.
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Activation Energy
2.6⊙��
Introduction
can require an input of energy before they will begin. For example, m
agnesium burns vigorously in
oxygen but it takes the heat of a bunsen flame to get it started.
This has led scientists to the idea that there is an energy barrier that has to be overcom
e for areaction to start. For som
e reactions the energy available at room tem
perature is already sufficient,
but for others much m
ore may be needed. Th
e energy barrier has become known as the ‘activation’
energy because it is the energy needed to ‘activate’ the reaction.
This lesson topic explores the idea of activation energy and how it affects chem
ical reactions.
{��
Energy During Collision
This activity looks at how the chem
ical energy of a reaction mixture changes as the reactant
molecules collide and change to form
the product molecules.
Imagine a very sim
ple reaction between two diatomic m
olecules.
A—
A +
B—B
2 A —
B
In order to react, the two reactant molecules m
ust first collide. During the collision, the original
broken and the product bonds are half made. Th
is highly unstable arrangement of atom
s exists only for the slightest fraction of a second before separating as the product m
olecules.
into each other and stop, their kinetic energy is entirely changed to potential energy.
This m
eans that, as the reaction between the twocolliding m
olecules progresses, their potential energy increases until the point of full collision. Th
en, as new bonds form
and the product molecules spring apart,
potential energy is changed back to kinetic energy until the potential energy has dropped to the value of the chem
ical energy of the product molecules.
The graph shows the energy pathway for two
colliding reactant molecules changing to
product molecules.
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Home Practice
2.5
Q1. In an experim
ent, 1 g of magnesium
metal was reacted with an excess
l -1). The volum
e of hydrogen gas
released was measured in cm
3 every ten seconds until the reaction
stopped after two minutes.
a)
Sketch a graph (no graph paper needed) of how the results
m
ight appear, showing
i)
labels for each axis, and
1
ii)
the shape of the graph.
1
b) l -1).
1
Q2. Citric acid can be neutralised by reacting it with excess
copper carbonate.
citric + copper
copper +
carbon + water
acid
carbonate
citrate
dioxide
D
escribe two possible ways of measuring the reaction progress.
2
Q3. In an experim
ent, 8g of chalk
was reacted with an excess
(i.e. 2 m
oll -1) in a flask.
The m
ass of the flask and its
contents was measured every
ten seconds for 200 seconds.
Th
e results were then plotted
on a graph, as shown.
a)
i)
did the reaction stop?
1
ii)
was the reaction fastest?
1
b)
Calculate the average rate of reaction between 60s and 110 s.
2
c) Sketch a graph (no graph paper needed) showing how the rate
of this reaction changes with time.
1
Total (10)
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munity - based on Challenge Chem
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Home Practice
2.3
affects the rate of a reaction.
Th
e reaction to be used is that
between hydrogen peroxide
and potassium iodide.
Th
e concentration of iodide ions is to be varied while the addition of a
little thiosulphate solution initially prevents the formation of iodine.
Q1. a)
1
b) H
ow can the stop-point for timing this reaction be determ
ined?
1
c)
i) H
ow is the relative rate calculated?
1
ii)
1
Q2. Th
e student carries out five experiments.
a)
How m
ight the concentration of potassium iodide solution be
varied in each experiment?
1
b)
iodide is increased?
1
c)
Sketch a graph (no graph paper needed) of how the results
m
ight appear, showing
i)
labels for each axis, and
1
ii)
the shape of the graph.
1
d) -1 for a concentration
2
Total (10)
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 18
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Temperature and Rate
2.4⊙��
IntroductionTh
ough no longer Prescribed Practicals, this sheet and the previous one provide the opportunity to becom
e familiar with the calculation of Relative Rates and practice in writing Investigation Reports.
Th
e purpose of this lesson topic is to investigate in more detail the way
that the tem
perature of reactants affects the rate of a chemical reaction.
{��
Considering The Investigation
The aim
of this experiment is to find the effect of varying the tem
perature on the rate of reaction between oxalic acid and an acidified solution of potassium
permanganate.
You do not need to understand the reactions involved in detail but the equation is given herefor inform
ation.
2 (aq) + 6 H+(aq)
4 -(aq) 2+(aq) + 10 CO
2 (aq) + 8 H
2 O2 (l)
oxalic acid
perm
anganate ions(colourless)
(intense purple)
(all colourless)
Initially the reaction mixture is deep purple in colour due to the presence of the perm
anganate ions but it turns colourless as soon as they are used up. Th
is colour change provides a convenient stop-point for tim
ing the reaction.
In this investigation only the temperature of the reaction m
ixture is to be varied. The
concentrations and volumes of the reactants will be kept constant.
Since the number of m
oles of permanganate ions present will be the sam
e in each experiment,
the disappearance of the purple colour will always represent the same extent of reaction.
So if t is the time it takes for the purple colour to disappear then 1/t
gives a measure of the
relative rate of reaction.
relative rate = 1/t
when t is in seconds (s), the unit for relative rate is 1/seconds or s -1
The idea is to carry out a series of four experim
ents and to time each experim
ent for a differenttem
perature of the reaction mixture.
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CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Self Check
2.5
Q1. During a chem
ical reaction the
concentration of a
A reactant is unchanged.
B product decreases.
C reactant decreases.
D
catalyst increases.
Q2.
carbon dioxide is given off and the final
solution is colourless.not be
suitable for following the progress of this
reaction?
A Volum
e of gas produced
B Colour of the solution
C
D Concentration of the acid
Q3. The graph shown was plotted from
the
reaction between zinc and sulphuric.
Th
e graph shows that the
A volum
e of hydrogen decreases with time.
B reaction rate increases with tim
e.
C hydrogen is produced at a steady rate.
D reaction rate is fastest at the start.
Q4. The rate of a reaction could be represented
by the
A
change in mass of a reaction m
ixture.
B volume of gas produced.
C change in concentration of a reactant
per unit tim
e.
D tim
e taken for reaction to go to
com
pletion
Q5. The graph shows the volum
e of oxygen
produced during a hydrogen peroxide
reaction.
the tim
e interval 2 - 4 minutes?
A
20 cm
3 min
-1
B
3 min
-1
C
10 cm3 m
in-1
D
3 m
in-1
Q6.
for magnesium
in sulphuric acid?
Questions 7 and 8 refer to these graphs of
reaction progress.
Q7. In which graph could the dotted line
represent a catalysed version of the same
reaction (all other variables being the sam
e)?
Q8. In which graph could the dotted line
represent the same reaction done at lower
tem
perature (all other variables being the
same)?
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munity - based on Challenge Chem
istry © R.I.S.EPage 26
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Example 2.
Effect of concentration on marble
reacting with acid (recording the m
ass of flask and its contents against tim
e).
the reaction is repeated with m
ore concentrated acid.
Think about the two progress graphs.
higher concentration give the lower graph?
Example 3.
Effect of a catalyst on zinc reacting in sulphuric acid (recording the volum
e ofhydrogen collected against tim
e).You are only provided with the uncatalysed graph. You need to add the catalysed version.
Think about the effect that catalysing the reaction with a tiny am
ount ofcopper will have on the progress graph (all other variables being the sam
e).
at the sam
e time as the ‘uncatalysed’ graph?
exactly the sam
e as in the ‘uncatalysed’ graph?
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 19
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
|���Th
e Experimental W
orkTh
is investigation should take about 40 minutes to com
plete. If you have insufficient tim
e tocom
plete it in this lesson ask your teacher’s advice as to what to do next.In this activity, a table of results is produced for a series of, short experim
ents using a differenttem
perature for each experiment.
Hazards:
Eye protection should be worn as sulphuric acid and
potassium
permanganate can irritate eyes. Potassium
permanganate will also stain skin so avoid contact or
wash imm
ediately.
1. Collect a 100 cm
3 beaker.
(best size of m
easuring cylinder or even a pipette) the following
mixture into the beaker.
2 cm3
potassium perm
anganate (0.02 m
ol l -1 )
40 cm
3 water
3 sulphuric acid
(1 m
ol l -1 )
(Th
e acid is added to provide H+(aq) ions for the reaction)
3. H
eat the beaker to about 40 °C. Once the tem
perature has
stopped changing, record the initial tem
perature.3 of oxalic acid (0.02 m
ol l -1 ) to the beaker and start
timer.
tim
er when the purple colour disappears. Record the reaction
time, t.
Think about how the investigation m
ight be carried out.
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 20
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
}���Processing the Raw Results
The purpose of this activity is to exam
ine the results by constructing a graph of the relativerate plotted against the tem
perature of each solution.Since the tem
perature of the reactants may fall over the course of the reaction we will use the
average of the initial and final temperatures as our reaction tem
perature.
1. Calculate the average reaction tem
perature for each experiment.
2. Calculate the relative rate for each experim
ent.
3.
On the graph provided in your notes, label the axes and decide
on a suitable scale for each axis.
4. Rem
ember to include the appropriate units for each axis.
line of best fit’.
Think about the graph you have drawn.
or in som
e other way?
the rate of reaction?
this investigation?
Think about the investigation you have just com
pleted.
such as room
temperature (20 °C).
Reliable?Precision? In what ways could you
have been m
ore precise?
Accuracy of any of your
measurem
ents? (Better equipment available?)
It is important, at the end of an Investigation, to reflect and evaluate your procedures.
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 25
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
}���Com
paring Reaction ProgressTh
e purpose of this activity is to compare progress graphs for the sam
e reaction taking place under different conditions.
Th
e three following graphs are reproduced in your Notes.
Example 1.
Effect of temperature on zinc
reacting in hydrochloric acid (recording the volum
e of hydrogen collected against tim
e).Keeping all other variables the sam
e, the reaction is repeated at higher tem
perature.
Think about your graph of average rate against tim
e.
then gradually? O
r gradually then rapidly?
4. Using graph paper provided in your N
otes, plot a line graph of the average rate in cm3 s -1
(vertical axis) against the tim
e elapsed in seconds (horizontal axis).
Use the mid-point of each tim
e interval as the position along the time axis for each plot. In
other words,
for tim
e interval 0 - 20 s
plot average rate at 10 s
for time interval
20 - 40 s plot average rate at 30 s
and so on
Think about the graphs in the diagram
.
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 24
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
|���Calculating Th
e RateYou have seen that the progress graph is steepest when the rate of reaction is fastest. So a fast rate gives a large change in a short tim
e, whereas a slow rate gives only a small change in the sam
e time.
Thus rate is concerned with the am
ount of change in a given time.
This activity exam
ines how the rate of reaction can be calculated from a progress graph.
Rate of Reaction is the change in quantity of a reactant or product per unit time.
Strictly speaking, since the rate of a reaction is changing all the time you can only calculate the
average rate during any time interval.
change in quantity
average rate =
change in time
The unit used for rate will depend on which type of quantity is involved (m
ass, volume, or
concentration) and whether the time is in hours, m
inutes or seconds. For example, for a change in
mass per m
inute the unit could be grams per m
inute (g/min). Th
e unit g/min can also be written
as g min
-1 where the negative index denotes ‘per’. For a change in gas volume per second the unit
could be stated as cm3 s -1 (cubic centim
etres per second).
The progress graph shown was
plotted from m
easurements taken
during the reaction of magnesium
with sulphuric acid whichproduces m
agnesium sulphate
and hydrogen gas.
1. Reproduce this graph on the
paper provided in your N
otes.2.
Calculate the change in volume
for each 20s tim
e interval.3.
Calculate the average rate for each 20s time interval and com
plete the table in your Notes.
Think about the experim
ent and your graph.
W
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 21
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Self Check
2.4
Q1. To examine the effect of tem
perature
on the rate of reaction, it is necessary to
A vary the concentrations of all the
reactants and keep the temperature
constant.
B keep the tem
perature constant and vary
the concentration of just one reactant.
C vary the concentration of one reactant
and change the temperature each tim
e.
D
keep the concentrations of all the
reactants constant and vary the
temperature.
Q2. The m
ixture becomes colourless because
A
the acid is neutralised.
B carbon dioxide is form
ed.
C the tem
perature rises.
D
the permanganate ions all react.
Q3. The reaction is tim
ed from
A the start until the colour just appears
B when the colour appears until the
reaction ends.
C the start until the colour disappears.
D
when the colour disappears until the
reaction ends.
Q4.
unimportant?
A
Temperature of the Reactants
B Size of beaker used for the reaction
C Volum
e of oxalic acid
D
Concentration of potassium
permanganate
Q5. If t is the time taken, and the tem
perature
of the mixture is T
, which expression is
used to calculate the relative rate?
A
1 / t
B
1 / T
C T / t
D
T - t
Q6.
the relative rate for the reaction?
A
s -1
B
s -1
C
0.04 s -1
D
0.02 s -1
Q7.
varies with temperature?
Q8. The reaction of perm
anganate ions with
oxalic acid is quite slow at 40 °C.
roughly twice as fast?
A 20 °C
B
C 80° C
D
400 °C
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 22
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Home Practice
2.4
affects the rate of reaction.
Th
e reaction to be used is that between oxalic acid and potassium
permanganate.
2 (aq) + 6 H+(aq)
4 -(aq) 2+(aq) + 10 CO
2 (aq) + 8 H
2 O2 (l)
Q1. a)
How can the stop-point for tim
ing this reaction be determined?
1
b) 1
c)
If the reaction times are m
easured in seconds what will be
the units for the relative reaction rates?
1
Q2. Th
e student carries out four experiments.
a)
1
b)
this investigation?
3
c)
Sketch a graph (no graph paper needed) of how the results
m
ight appear, showing
i)
labels for each axis, and
1
ii)
the shape of the graph.
1
d)
have on the rate of reaction?
1
Total (10)
KHS June 2014 - Cheviot Learning Com
munity - based on Challenge Chem
istry © R.I.S.EPage 23
CfE New H
igher - Unit 1 - Topic 2Study G
uide - Reaction Rates
Reaction Progress
2.5⊙��
Introduction
missed out com
pletely if time is short, though it is m
ore skills than knowledge.Relative Rates are very useful but can only provide an average over a certain part of the reaction. H
owever, as any chemical reaction progresses from
its start to its finish the rate is changing all the tim
e. So how can the speed of reaction be followed as a reaction progresses?
This lesson topic deals with som
e ways of following the progress of a chemical reaction.
{��
Progress Of A Reaction
During any reaction the quantity of the reactants decreases and the quantity of the products
increases. If the decrease or increase in any substance in the reaction can be measured then the
progress can be followed. The m
easurement could be a m
ass, a volume, or a concentration.
The aim
of the following experiment is to follow the progress of a reaction by recording the
volume of gas produced at regular tim
e intervals.In the reaction to be used, pieces of m
arble (calcium carbonate) react with hydrochloric acid
(hydrogen chloride) to produce calcium chloride, water, and carbon dioxide gas.
1. Collect a tim
er (stopclock) and the apparatus needed for the
experim
ent shown. (How is the m
easuring cylinder to be held in
place?)
2. Start the experim
ent and record the volume of the gas at regular
or even 2 m
ins depending on how fast the reaction is).
3.
On the graph provided in your notes, plot a graph of gas volum
e
against time, and draw a ‘line of best fit’.
4. Rem
ember to include the appropriate units for each axis.