1.1 1.1 RATE OF REACTIONRATE OF REACTION
Why a tall building can be destroyed Why a tall building can be destroyed with explosives within seconds??with explosives within seconds??
Why food has to take several hours Why food has to take several hours
to be decay ?? to be decay ??
Why do coal mines face a high risk Why do coal mines face a high risk of explosion ??of explosion ??
All these are because :All these are because :difference of difference of
rate of reactionrate of reaction
What is the rate of reaction ?
The speed at which reactants are converted into products in a
chemical reaction
For examples:
1. Fireworks display occurs in just a few seconds
Rate of reaction HIGH
2. The photosynthesis process takes a few hours
Rate of reaction LOWER
3. The erosion process of stones takes many years
Rate of reaction VERY LOW
Some reactions are fast & some reactions are very slow
So do the chemical reactions in laboratory
How we determine & calculate the rate of chemical reactions
in laboratory ??
It just same with the way we calculate the speed of driving
How we calculate the
speed of driving ??
Yes, the formulae is :
Speed = distance (km) time (hour)
In the other hand, it is :
Rate of = physical changesreaction time
What are the changes that we could measure??
Mass before and after experiment (gs-1)Colour changesTemperature changes (°Cs-1)Pressure changes (Ps-1)Volume of gas liberated (cm3
s-1) (only if the reaction produce gases)
A + B C + D
(reactants) (products)
During the chemical reaction, reactants will become less but products become more
Decomposition of hydrogen peroxide to form water and oxygen gas
H2O2 (aq) H2O (l) + O2 (g)
For any chemical reaction, we can measure its
average rate of reaction & rate of reaction at a given time
Rate of = physical changesreaction time
average rate of reaction
rate of reaction at a given time
Average rate = total changesof reaction total time taken
Rate of reaction at a given time = gradient of the curve at that instant= y2 – y1 / X2 – X1
Volume of hydrogen gas ( cm3 )
Time ( s )
Total changes
Total time taken
Average rate = total changesof reaction total time taken
Volume of hydrogen gas ( cm3 )
Time ( s )
Changes = y2 – y1
time taken = X2 – X1
Rate of reaction at 90 second = gradient of the curve at that instant
= y2 – y1 / x2 – x1
1. find the given time2. draw a line to curve3. draw a tangent4. Measure y2 – y1
5. Measure x2 – x1
Let’s see an example:
burette
water
Hydrochloric acid
Marblechips
Hydrogengas
CaCO3 + HCl CaCl2 + H2O + H2
Volume of hydrogen gas was recorded every 30 seconds
. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . after 10 minutes . . .
Here’s the result :
Time / s
Reading of burette
/ cm3
Volume of gas/ cm3
Then we plot the graph: Volume of hydrogen gas ( cm3 )
Time ( s )
5
10
0
35
30
25
20
15
6030 90
180210
240270
300150
120
Get the answers:
a) Calculate the average rate of reaction between marble chips and hydrochloric acid.
Solution: refer to table
Time / s
Reading of burette
/ cm3
Volume of gas/ cm3
Average rate of reaction = total changes / total time taken
Average rate of reaction = 34 cm3
300 s
= 0.113 cm3 s-1
** you’ll get the same answer by using graph
b) Calculate the average rate of reaction in the first 90 seconds.
Solution:
Time / s
Reading of burette
/ cm3
Volume of gas/ cm3
this is accumulated !!
Average rate of reaction = total changes / total time taken
Average rate of reaction = 20 cm3
90 s
= 0.222 cm3 s-1
** you’ll get the same answer by using graph
c) Calculate the rate of reaction at
a) 60 second
b) 210 second
5
10
35
30
25
20
15
Time ( s )
90
Volume of hydrogen gas ( cm3 )
060
30180
210240
270300
150120
Solution (a) :
22.00 – 10.50= 11.50 cm3
90-30 = 60 s
Rate of reaction at 60 second
= y2 – y1
x2 - x1
= 22.00 -10.50
90 -30
= 11.50 cm3
60 s
= 0.192 cm3 s-1 **
5
10
35
30
25
20
15
Time ( s )
90
Volume of hydrogen gas ( cm3 )
060
30180
210240
270300
150120
Solution (b) :
35.50 – 30.00= 5.50 cm3
255-160 = 95 s
Rate of reaction at 210 second
= 35.50 -30.00
255 -160
= 5.50 cm3
95 s
= 0.058 cm3 s-1 **
d) Compare the rate of reaction at
60 second and 210 second
Solution:Rate of reaction at 60 second = 0.192 cm3 s-1
Rate of reaction at 210 second = 0.058 cm3 s-1
- The rate of reaction at 60 second is higher than 210 second.
- This means the reaction occurs faster at the moment of 60 second
e) Why the rate of reaction at 60 second is higher than 210 second ?
Solution:
- Because the concentration of reactants is decreasing during the chemical reaction.
f) There are no more hydrogen gas liberated after 300 second, why?
Solution:- Because the chemical reaction is
stopped- All the marble chips had been reacted
Rate of reactionvery high
Rate of reaction
lower
Curve becomes horizontal lineNo more reaction occur
Rate of reaction = 0 cm3 s-1
Rate of reaction
More lower
Total volumeof gas
Liberated (cm3)
Time (s / min)
Learning Task 1.2page 8
Some reactions are fast & some reactions are very slow
So do the chemical reactions in laboratory
What are the factors affect the
rate of reaction ??
2. Temperature
1. Total surface area
4. Catalyst5. Pressure
3. Concentration
2T 2C 1P
How does the factors ofTotal surface area,
Temperature, Concentration,
Catalyst & Pressure
affect the reaction rate??
2T
2C
1P
Let’s do the experiment to investigate that:
1.Surface area smaller , rate of reaction2.Concentration higher, rate of reaction3.Temperature higher, rate of reaction4.Catalyst added, rate of reaction
Surface area smaller , rate of reactionConcentration higher, rate of reactionTemperature higher, rate of reactionCatalyst added, rate of reactionPressure higher, rate of reaction
Problem solving
A + B C + D
(reactants) (products)
- During the chemical reaction, reactants will become less but products become more
- The chemical reaction will stop once one of the reactants is used up.
Pattern of graphs
Reactant A + Reactant B gases
Less Less More
Mg (s) + HCl (aq) Mg (s) + HCl (aq) MgCl (aq) + H MgCl (aq) + H22 (g) (g)excess
Draw out the curves of graph for:1. Magnesium mass / 2. Hydrochloric acid concentration/ 3. Magnesium chloride concentration /4. Hydrogen gas volume against the time
1. the curves of graph for Magnesium mass against the time
Magnesium Excess
>>>
2. the curves of graph for hydrochloric acid concentration
against the time
Hydrochloric acidLimited reactant
3. the curves of graph for magnesium chloride concentration
against the time
Hydrochloric acid has been used up &
reaction stopped
4. the curves of graph for hydrogen gas volume against the time
Hydrochloric acid has been used up &
reaction stopped
Q1. Compare these:Set 1 : 1g of zinc plate (excess) reacts
with sulphuric acid 0.1 mol dm-3 to form zinc sulphate and hydrogen gas
Set 2 : 1g of zinc powder (excess) reacts with sulphuric acid 0.1 mol dm-3 to form zinc sulphate and hydrogen gas
Find the difference !!
Hydrogen Gas / cm3
Time / s
Set 2
Set 1The number of moles
of chemical subtances are same
Factor : total of surface area /
Particle size
Q2. Compare these:Set 3 : 1 g of zinc powder (excess) reacts
with 500cm3 sulphuric acid 0.1 mol dm-3 to form zinc sulphate and hydrogen gas
Set 4 : 1 g of zinc powder (excess) reacts with 250cm3 sulphuric acid 0.2 mol dm-3 to form zinc sulphate and hydrogen gas
Find the difference !!
Hydrogen Gas / cm3
Time / s
Set 4
Set 3The number of moles
of chemical subtances are same
Factor : Concentration
Q3. Compare these:Set 5 : 1 g of zinc powder (excess) reacts
with 250cm3 sulphuric acid 0.1 mol dm-3 to form zinc sulphate and hydrogen gas
Set 6 : 1 g of zinc powder (excess) reacts with 250cm3 sulphuric acid 0.2 mol dm-3 to form zinc sulphate and hydrogen gas
Find the difference !!
Hydrogen Gas / cm3
Time / s
Set 6
Set 5
The number of moles of chemical subtances
are same
Factor : Concentration
Q4. Compare these:Set 7 : 1 g of zinc powder (excess) reacts
with 25cm3 sulphuric acid 0.15 mol dm-3 to form zinc sulphate and hydrogen gas
Set 8 : 1 g of zinc powder (excess) reacts with 50cm3 sulphuric acid 0.1 mol dm-3 to form zinc sulphate and hydrogen gas
Find the difference !!
Hydrogen Gas / cm3
Time / s
Set 8
Set 7
The number of moles of chemical subtances
in Set 8 is higher, so the volume of gas
realeased is higher
Factor : Concentration
Find out what they means!!CollisionCorrect orientation Activation energyEffective collisionCollision frequencyEffective collision frequencyEnergy profile diagram
Achieve effective collision
Base on kinetic theory, particles moves constantly and collide each other all the time
However, majority of collisions do not lead to a reaction,why ?
Only those in which the colliding species have:
Achieve minimum amount of energy, called the ACTIVATION ENERGY, Ea
And with CORRECT ORIENTATION
EFFECTIVE COLLISIONS
For a reaction to take place, the particles of the substances that are reacting have to collide. If they collide, with enough energy then they will react.
The minimum amount of energy that particles need to react is called the ACTIVATION ENERGY
Activation energyActivation energy
therefore some main ways of increasing the rate of a reaction:
1) increase the number of collisions2) increase the amount of kinetic energy so that more collisions lead to a reaction3) decrease the energy activation so that more reactants could be reacted
what factors could cause 1, 2, 3?
Size of solid reactant smallerTotal surface area exposed to collision
with other reactant particle is biggerThe frequency of collision between
reactant particles increaseFrequency of effective collision increaseRate of reaction higher
Higher temperatureHigher temperatureKinetic energy of reactant particles increaseKinetic energy of reactant particles increaseParticles move faster and collide more oftenParticles move faster and collide more oftenThe frequency of collision between
reactant particles increaseFrequency of effective collision increaseRate of reaction higher
Higher concentrationMore number of particle per unit volume of
solutionThe frequency of collision between
reactant particles increaseFrequency of effective collision
increaseRate of reaction higher
Positive catalyst usedenables the reaction occur through an
alternative path which requires lower activation energy
More colliding particles are able to achieve the lower activation energy
Frequency of effective collision increase
Rate of reaction higher
Activationenergy Lower
Activationenergy
Higher pressureMore number of particle per unit volume
of solutionThe frequency of collision between
reactant particles increaseFrequency of effective collision
increaseRate of reaction higher
Conclusion
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