The document covers essential aspects of reaction kinetics, including rate of reaction, collision theory, and the effects of temperature and catalysts. It explains how to determine the order of reactions experimentally and details various methods for studying reaction rates. Additionally, it includes examples of catalysts in industrial processes and environmental applications, such as the Haber process and catalytic converters.

1. +
Reaction Kinetics (A2)
Prepared by: Faiz Abdullah

2. +
AS recap
In As level, you should know what is:
 Rate of reaction
 Collision theory
 Boltzmann distribution of energy
 Catalyst
 Activation Energy
 Effect of temperature, concentration and catalyst on rate of
reaction

3. +
For A2,
we are dealing with
DATA MANIPULATION

4. +
Order of Reaction
What do you mean by order?

5. +
Measuring rate of reactions
Usually, we are looking at HOW FAST THE CONCENTRATION
OF REACTANTS IS FALLING AT ONE TIME.
Suppose we have:
A(aq)+B(g)  Products
We can measure rate of reaction with:
-The decreasing concentration of A in mol/dm3 in 1 min.
-The decreasing volume of gas B in 1min

6. +
Orders of reaction
Suppose of you have: A + B  products
From the experiment: you found out that….
When [A] doubles, rate doubles.
Rate of reaction is proportional to [A]
Therefore, order with respect to A is 1
When [A] doubles, rate increases four times
Rate of reaction is proportional to [A]2
Therefore, order of reaction w.r.t. A is 2
When [A] doubles, rate of reaction does not change
Rate of reaction does not depend on [A]
Therefore, order w.r.t A is 0
WARNING:
YOU CANNOT DEDUCE THE ORDER OF
REACTION JUST BY LOOKING AT THE
EQUATION!!!!
ORDERS OF REACTIONS ARE ALWAYS FOUND
BY DOING EXPERIMENTS

7. +
Rate equation
Suppose A + 2B + C  products
From experiments, we found out that:
[A] doubles, rate of reaction doubles
Therefore, order w.r.t A is 1
[B] doubles, rate of reaction increases
by 4
Therefore, order w.r.t B is 2
[C] doubles, rate of reaction does not change
Therefore, order w.r.t C is 0
Rate Equation:
Rate = k [A] [B]2
Where k is rate constant

8. +
Why is C in the chemical equation
but not in the rate equation????
Some reactions occur in multiple steps:
Step 1: A + 2B  2C + D
Step 2: C + D  products
Final : A + 2B + C  products
SOME STEPS ARE SLOW AND SOME ARE FASTER
SLOW
FAST
THIS STEP IS THE
RATE-DETERMINING
STEP
OVERALL REACTION RATE
DEPENDS ON THE SLOW STEP
WHEN you measure rate of reaction, what you are actually
Measuring is the rate of the determining step!!!

9. +
Rate constant, k
Rate = k [A] [B]
Rate constant is constant (does not change value) only when
concentrations of reactants are changing.
RATE CONSTANT CHANGES WHEN:
1. TEMPERATURE CHANGES
2. ADDING CATALYST

10. +
DEDUCING ORDER BY INTIAL
RATES METHOD
Run Initial [A]/mol Initial [B]/mol Initial rate/mols-1
1 1.00 1.00 1.25 x 10-2
2 1.00 2.00 2.5 x 10-2
3 2.00 2.00 2.5 x 10-2
Can you find the rate equation? Can you find k?
Make [A] constant,
[B] x 2, rate x 2
Order w.r.t B is 1
Make [B] constant,
[A] x 2, rate same
Order w.r.t A is 0
Rate = k [B]
k=1.25 x 10-2 s-1

11. +
Deducing order from graphs
First- order reaction
Zero-order reaction

12. +
Rate concentration graph

13. +
Graphs Summary

14. +
Half-life of first-order reaction
Half life  time taken to get half of the final concentration

15. +
Half-life equation
Half-life (in seconds) can be used to find k, rate constant:
T1/2 = ln (2) / k

16. +
EXPERIMENTAL TECHNIQUES
FOR STUDYING RATES
① Sampling followed by titration
② Using a colorimeter
③ Measurement of gas evolved

17. +
CATALYST
① Homogenous: catalyst same phase as the reactants
② Heterogeneous: catalyst and reactants different phases

18. +
CATALYSIS
In AS, you need to know FOUR SPECIFIC EXAMPLES

19. +
1) HABER PROCESS
N2 + 3H2  2NH3
Catalyst: Iron
Note: Transition metals are good at acting as catalysts because
their atoms have unfilled d-orbitals.
Gases are adsorbed on to the surface of the metal, forming weak
bonds.
① Formation of bonds with the metal surface weakens the
bonds within the gas molecules
② The orientation of the adsorbed molecules may be favorable
for the reaction
THIS IS A
HETEROGENEOUS
SYSTEM

20. +
2) Catalytic converters in vehicle
exhausts

21. +
 Catalytic converters in vehicle exhausts aim to remove a
number of pollutant gases from vehicle exhausts.
 Pollutants: Nitrogen oxides, carbon monoxides.
 Inside the ceramic honeycomb, it has a very thin coat of:
o Platinum and palladium: oxidize CO and unburnt hydrocarbons
o Platinum and rhodium: reduce NOx to N2

22. +
3) Nitrogen oxides in the
atmosphere
 Studies on acid rain have concluded that in the atmosphere the
presence of oxides of nitrogen, particularly NO2, increases rate
of oxidation of SO2  SO3.
 NO2 remains unchanged and is thought to form a weak
intermediate with SO2.

23. +
4) The role of Fe2+ in I-/S2O8
2-
reaction
Step 1: S2O8
2- + 2Fe2+  2 SO4
2- + 2Fe3+
Step 2: 2Fe3+ + 2I-  2Fe2+ + I2
Overall reaction: S2O8
2- + 2I-  2Fe2+ + I2
Fe2+ does not change overall
Although there are two steps,
Ea is lowered overall