SPM Chemistry Form 4 Chapter 1

7/29/2019 SPM Chemistry Form 4 Chapter 1

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RATE OF REACTION

Definition

Speed at which reactants are converted into

products in a chemical reaction.

Fast reaction;

- time taken is short

So, the reactants is quickly converted to theproducts.

Thus, the rate of reaction is high/higher.


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Slow reaction;- time taken is long

So, the reactants is slowly converted to the

products.

Thus, the rate of reaction is low/lower.


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So;

What is the relation between rates of reaction with

time?

When the time taken is short, the rate of reaction

is higher,

When the time taken is longer, the rate of

reaction is lower,

Rate of reaction is directly proportional with

1/time

Rate of reaction is inversely proportional with

time


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Measuring the rate of reaction

Suitable changes;

volume of gas liberated

precipitate formation

change in mass during the reaction

colour changes

temperature changes

pressure changes

Changes in selected quantityRate of reaction= ________________________________________

Time taken


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Average rate of reaction :

The average value of the rate of reaction within a

specified period of time.

Notes:

Reaction with high rate of reaction,

completed in short time.

Reaction with low rate of reaction,

completed in longer time.

Average rate

of reaction

balas=

Changes in selected quantity

____________________________________________

Time taken


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Rate of reaction at given/Instantaneous time :

The actual rate of reaction at that instant.

(a.k.a : Instantaneous rate of reaction)

The formula

31.8 cm3

90 s

0.35 cm3 s-1

Instantaneous

rate of reaction

balas

=

Average rate

of reaction

balas=

Total volume of gas liberated

____________________________________________

Time taken

Gradient of the curve at that instant

=

=


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ii. The rate of reaction at 90 seconds?

(Instantaneous rate of reaction)

Solutions: - Plot a graph

- Draw a tangent

- Find the gradient

The rate of reaction at 90 seconds= gradient at 90 seconds

= Length of DF

Length of EF

= 0.14 cm3s-1

B: Factors Affecting The Rate of Reaction

Instantaneousrate of reaction

at 90 seconds= Gradient of the curve at 90 seconds


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Why these two graph different?

a) Total surface area of solid reactant

b) Concentration of reactantc) Temperature of reactant

d) Use of catalyst

e) Pressure of gaseous reactant

Collision Theory


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Dear boys and girls to better understand of

collision theory you must know few thing

related to the theory which is;

Collision

Effective collision

Activation energy

Collision frequency

Effective collision frequency Energy profile diagram

* And also the chemical equation


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What is the Collision Theory?

During a reaction, the particles of the reactants

must collide with each other, forbondbreaking and then bond formation to occur to

produceproduct.

Bond breaking : absorb heat energy

Bond formation: release heat energy

Those collisions which achieved a minimum

activation energy and with the correct

orientation will result in a reaction. These

collisions are called effective collisions.

If the particles collide with less energy than

activation energy or with wrong orientation, it

will not result in reaction, is called ineffective

collisions.

So what is i. effective collisions?

ii. activation energy?


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Effective collisions

Those collisions which achieved a minimum

activation energyand with the correct orientation, will result in

a reaction.

Activation Energy

Activation energy is the energy barrier that

must be overcome by the colliding particles

of the reactants in order for reaction to occur


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Energy Profile Diagrams

i. Exothermic Reactions

Remember the process and diagrams, we will

study more when we reach topic 4.

Energy

Reactants

Products

Activation Energy

Exothermic Reaction

Reaction path

Heat changes


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ii. Endothermic Reactions

Activation energy is the difference in energy

between the energy in reactants and the

energy at the peak of curve

Energy

Reactants

Products

Activation Energy

Endothermic Reaction

Reaction path


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Exothermic Reaction

Reactants Product

Total Heat

Energy

Higher Lower

Heat Energy

during

reaction

Energy

absorbs

during bond

breaking is

lower

Energy

releases

during bond

formation is

higherThus;

Heat changes = Heat Energy in product

Heat Energy in reactant

= - ve


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Endothermic Reaction

Reactants Product

Total Heat

Energy

Lower Higher

Heat Energy

during

reaction

Energy

absorbs

during bond

breaking is

higher

Energy

releases

during bond

formation is

lowerThus;

Heat changes = Heat Energy in product

Heat Energy in reactant

= + ve

The conclusion is;

The reaction occur when reactants collide;

a. achieved activation energy

b. with correct orientation

Any Question so far?


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1 Effect of surface area/size

SMALLERsize solid reactant,

Bigger total surface area per volume

Higher frequency of effective collision

Higher rate of reaction

BIGGERsize solid reactant,

Smaller total surface area per volume

Lower frequency of effective collision

Lower rate of reaction

Sketch graph volume of gas against time


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Base from the graph, please explain?

I : Small marble

II : Large marble

Volume of

gas / cm3

Time / min

I II

V

t1 t2


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- Graph I is more steeper than graph II

- Thus, the gradient of graph I is more than

graph II

- Thus, the rate of reaction for the experiment Iis higher than experimen II

Question: Why the total volume of gas is

same?

Answer: the number ofmole of reactant

is same

HW: draw graph figure 1.6pg10


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Effect of Size

When the size of fixed mass of solid reactant

(name the reactant, CaCO3)issmaller,

The total surface area per volumeexposed to collision with other reactant

(name the reactant) particlesisbigger.

Thus, the number of collision among the

reacting particles at the surface ofthe

solid reactantsincreases. Frequency ofcollission is higher.

Thus, the number of collision achieved

the activation energy to become effective

collision is alsoincreases.

This lead to anincreasein theFREQUENCYofEFFECTIVE

COLLISION.

Hence, ahigherrate of reaction.

Effect of Concentration

When the concentration of the solution of a

reactant increases;


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The number of particles per unit volume

of the solution of the reactant also

increases.

Thus, the number of collision among thereacting particles increases. Frequency

of collission is higher.



collision is alsoincreases. This lead to anincreasein the frequency

of effective collision.


HW: draw graph figure 1.8 pg11HW: draw graph figure 1.9 pg12

Effect of Temperature

When the temperature of a reactant increases;

The kinetic energy of reacting particles

will increase, so the particles moves

faster.


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Thus, the number of collision among the

reacting particles increases. Frequency

of collission is higher.

Thus, the number of collision achievedthe activation energy to become effective


This lead to anincreasein the frequency



HW: draw graph figure 1.10 pg13

draw graph figure 1.11 pg13

Effect of Catalyst

(Pg 13)

Catalyst: a substance which alters the rate of

chemical reaction while it remainschemicallyunchanged at the end of

the reaction.

Properties of catalyst;


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When the catalyst is presence;

The catalyst allows the reactian to take

place through an alternative path whichrequires a lower activation energy.

Thus, more collision among the reacting

particles are able to achive the lower

activation energy.

Thus, the number of collision achievedthe activation energy to become effective


This lead to anincreasein the frequency


Energy

Reactant

Ea

Product

Ea

: Activation energy

without catalyst

Ec

: Activation Energy

with catalyst

Ec

Reaction with

catalyst

Reaction without

catalyst

Reaction path


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Effect of PressureWhen the pressure of the gas of a reactant

increases;

The number of particles per unit volume

of the gas of the reactant also increases.

Thus, the number of collision among thereacting particles increases. The

frequency of collision is increase.



collision is alsoincreases. This lead to anincreasein the frequency



HW: pg. 25 EPC no. 1, 2, 4


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Sketch graph:

(i) Concentration of solution against time

(ii) Concentration of solution against 1/time

Concentration of sodium thiosulfate

(Na2S

2O

3) / mol dm-3

Time / s


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So, what can you conclude from the graph?

(iii) Temperature against time

____

time1 /s-1

Concentration of sodium thiosulfate

(Na2S

2O

3) / mol dm-3

Temperature / oC

time /s


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Temperature is directly proportional

to the rate of reaction

(iv) Temperature against 1/time

So, what can you conclude from the graph?

Concentration is directly proportional

to the rate of reaction

Suhu /

o

C

1time_____ /s-1


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How to analyse the graph?

First Situation:All of these experiments are using the same size

and mass of catalyst. The temperature of the

reactants remains the same.

Why are there differences in the rate of reaction

shown?


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I and II

I and III I and IV [comparison]

Please remember that the total volume of the gasdepends on the number of moles of the reactant.

Number ofmoles = Molarity Volume

(solution) 1000

Can you analyse the graph based from the

volume and the concetration of the reactant?

Volume of gas / cm3

Time / min

I II

V

t1 t2

III

IV

V/2


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Second Situation:

All of these experiments are using the same type

of catalyst. The volume, concentration andtemperature of the reactants remains the same.

Why are there differences in the early rate of

reaction shown?


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The size of catalyst in exp I is smaller compare

to exp II and III.

Or

The mass of catalyst in Exp I is more than exp II

and III.

Or

The size of reactant in exp I is smaller than exp

II and III

I II IIIVolume of the

gas / cm3

V

t1

t2 Time / min


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5.2

Exercise:An experiment is carried out between 10 g

of magnesium with 20 cm3 hydrochloric acid

0.5 mol dm-3. The reaction is completed in 8

minutes.

[Relatif atomic mass: H, 1; Cl, 35 ; Mg, 24;Molar volume of gas is 24 dm3 at room

condition]

a) Write a balanced chemical equation

for this reaction.b) Calculate the maximum volume of the

gas liberated at room condition.

c) Calculate the average rate of reaction

within 8 minutes.

d) Calculate the mass of the magnesiumused in the reaction.

e) Sketch the graph of volume against

time for these experiment


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The formula:

IF REACTANT IS SOLID

Number of mole = . mass .

Ar or Mr

IF REACTANT IS SOLUTION

Number of moles = Molarity Volume

1000

VOLUME OF THE GAS AT ROOM

CONDITION

Volume of = Number of moles 24 dm3

the gas


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Solution:

a. Mg + 2HCl MgCl2 + H2

0.01

b. Number of moles of Mg

= mass Mg

Ar

= 1024

= 0.42 mol (EXCESS-

BERLEBIHAN

Number of moles of hydrochloric acid

= Concentration Volume

1000

= MV

1000= 0.5 x 20

1000

= 0.01 mol


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Mg + 2HCl MgCl2 + H2

0.42 (0.01)

FBCE;2 mol HCl produce 1 mol H20.01 mol HCl produce x 0.01 mol H2

Thus;

The no. of mole of H2 = 0.005 mol

(1 mol of gas = 24 dm3 in room condition)

Volume of H2 = 0.005 X 24 dm3 H2

= 0.12 dm3= 120 cm3

c. Average reaction in 8 minute

= 120 / 8 cm3 min-1

= 15 cm3

min-1

d.

FBCE;


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2 mol HCl reacts with 1 mol Mg

0.01 mol HCl reacts with x 0.01 mol Mg

Thus;The no. of mole of Mg = 0.005 mol

(1 mol of Mg = 24 g)

Mass of Mg = 0.005 X 24 g= 0.12 g

HW: pg. 28-29 RQ obj.Q no. 1-8 (copy-paste)

pg. 29 Sub.Q no. 1pg. 30 Ess.Q no. 2

2. An experiment is carried out between 2 g

of magnesium carbonate with 20 cm3

hydrochloric acid 0.2 mol dm-3 .

(RAM: H, 1; C, 12; O, 16; Mg, 24;Molar volume of gas is 22.4 dm3 at s.t.p)

a) Write a balanced chemical equation

for this reaction.


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b) Calculate the maximum volume of the

gas liberated at s.t.p.

c) Draw a labbeled apparatus for

experimet.d) How to test and confirm the gas

liberated

Solution;

a) MgCO3 + 2HCl MgCl2 + CO2 + H2O

b) No. mol of HCl = MV/1000

= 0.2 x 20 / 1000

= 0.004 mol

FBCE;

HCl CO2

2 mol 1mol

0.004 mol 0.002 mol

No. of mol CO2 = 0.002 mol

Volume of CO2 = 0.002 x 22.4 dm3

= 0.0448 dm3


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= 0.0448 x 1000 cm3

= 44.8 cm3

d) Add 20 cm3 lime water into a test tube, and

passed through the gas into the test tube.

The lime water turns cloudy/chalky.

SPM Chemistry Form 4 Chapter 1

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