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Summary (CAIE) Cambridge A Level Chemistry (9701)
Summary & 15’s Chemical Kinetics Problems with Solution

Chemical Kinetics

Solution Concentration
MOLARITY
M=

𝒏
𝑽

DILUTION

MIXING

M1V1 = M2V2

M = M1V1 + M2V2
V1 + V2

M1, M2 = molarity of the

M = 
...
%

solution before and after

M = molarity of the mixed

M = solution molarity

dilution

solution

n = number of moles of

V1, V2 = volume of the

M1, M2 = molarity of

solution before and after

solutions 1 and 2

Mr

solute
V = volume of solution

dilution

 = density (g/mL)

V1, V2 = volume of
solutions 1 and 2

% = content (% of mass)
Mr = relative molecular
mass

Reaction Rate Concept
Reaction rate is the rate at which reactants are reduced or the rate at which
products are formed

v=-

[𝑹]
𝒕

or v = +

[𝑷]
𝒕

v = reaction rate (M/s or Ms-1)
-

[𝑅]
= the rate of reduction in the molar concentration of one of the
𝑡

reactants per unit time
+

[𝑃]
= the rate of increase in the molar concentration of one of the
𝑡
products per unit time

Note:
Rate of decomposition of reactants / rate of formation of products is
proportional to the coefficient
...
A reaction occurs due to collisions between reacting particles
...
Not all collisions result in a reaction
...

3
...

4
...


A+B

AB

Reactant

Product

possible
collision

colliding
particles A

no reaction
occurs

colliding
particles B

no reaction
occurs

collision of
particles A and B

not enough
energy

no reaction
occurs

enough
energy

reaction occurs

Activation Energy in Exothermic Reactions

Reactant

Product

Activation Energy in Endothermic Reactions

Product

Reactant

Factors Affecting the Reaction Rate:
1
...
Particle Size(s): Particle Size 
Frequency

Collision Frequency

Touch Surface Area 
Reaction Rate 

3
...
Temperature(s, l, aq, g): Temperature 
Kinetic Energy 
Enough Reactant Energy 
Reaction Rate 
5
...
A catalyst is a substance that can speed up a reaction, but
the substance itself is not changed chemically at the end of
the reaction
...
The way a catalyst speeds up a reaction is by lowering the
activation energy

Reactant
Reactant

Product

Effect of Catalysts on Endothermic Reactions

Product

Reactant

Catalyst Types
1
...

2
...

3
...

4
...
Does not undergo any lasting change in reactions, but may be involved
in reaction mechanisms
...
Speed up the rate of reaction, but does not change the type or amount
of reaction products
...
Lowers the activation energy, but does not change the enthalpy change
for the reaction
...
Changing the mechanism by providing steps that have a lower
...

5
...

6
...

7
...


Reaction Rate Equation
On reaction:
aA + bB
cC + dD

x

v = k[A] [B]

y

v = reaction rate (M/s or Ms-1)
k = reaction rate constants
[A], [B] = concentration of A and B
x = order of reaction to A
y = order of reaction to B
x + y = total reaction order

Reaction Rate Constant: a constant that depends on the type of reactant,
pressure, temperature and catalyst
...


Meaning of Reaction Order
1
...
First order: if the concentration of the reactants is increased n times,
then the reaction rate also increases n times

3
...
How many grams of solid sodium hydroxide (NaOH) are needed to
make 100 mL of 0
...

M=

𝑛
𝑉

0,2 =

𝑛
0,1

n = 0,02 mole

m = n
...
(23+16+1) = 0,8 grams solid NaOH
02
...
8 kg/L
...
What is the molarity of the concentrated sulfuric acid solution?
Ar S=32, O=16, H=1
b
...
1M,
then what is x?

Ans
...
M = 
...
% = 1,8
...
98 = 18M
Mr
98
b
...
V1 = M2
...
10 = 0,1
...
A total of 100 mL of 0
...
3M
HCl solution
...

M = M1
...
V2 = 0,1
...
400 = 130 = 0,26 M
V1 + V2

100 + 400

500

04
...
At a certain temperature and pressure,
the rate of formation of ammonia gas is 2x10-4 M/s, determine the rate
of reduction of nitrogen gas and hydrogen gas
...

N2 + 3 H2

2 NH3

[NH3] = 2
...
2
...
2
...
10-4 M/s
2

05
...
8 mol of N2O4 gas is heated to a certain temperature,
until it decomposes into NO2 gas
...
6 moles of NO2 gas, determine the average rate of decomposition
of N2O4 gas
...

N2O4 which reacted as much:
N2O4
S 0,8
R 0,3
L 0,5

2 NO2
0,6
0,6

1
2

x 0,6 = 0,3 mole

S = start reaction
R = react
L = leftover

Molarity of decomposed N2O4:

𝟎,𝟑

= 0,06 M
5
The average speed of decomposition of N2O4 gas is
- [N2O4] = -0,06 = - 0,015 M/s
t
4
06
...
After 15 seconds, it
turns out that there are still 0,3 moles of water vapor in the room
...
01M/s,
determine:
a
...
The initial number of moles of water vapor in the chamber

Ans
...
-[H2O] = (2/1) x 0,01 = -0,02 M/s
t
b
...
4 = 1,2 moles
The initial number of moles of water vapor: 0,3 + 1,2 = 1,5 moles
07
...
Also give a brief reason why this method can increase the rate
of reaction based on the collision theory
...
Mg(s) + HCl(aq)

MgCl2(aq) + H2(g)

b
...

a
...
Increase the concentration of HCl: to increase the number of HCl
particles and the frequency of collisions between HCl and Mg
particles
...
Reducing the size of the Mg particles: increase the surface area of
the contact area to increase the likelihood of collisions of Mg and HCl
particles
...
Increase temperature: to increase kinetic energy
...
Use catalyst: to reduce activation energy
...
i
...
Increase temperature
iii
...
For every 10°C increase in temperature, the reaction speeds up 2 times
...

Ans
...
The following provides data from the experimental results of the
reaction rate 2A(g) + B(g)

a
...

c
...

e
...


A2B(g) under various conditions:

Trial

[A] [B]

[B] [M]

v [M/s]

1

0,1

0,1

1,25x10-2

2

0,2

0,1

5x10-2

3

0,1

0,2

10-1

Determine the order of the reaction to A
Determine the order of the reaction to B
Determine the total of the order of reaction
Determine the value and unit of the reaction rate constant (k)
Write down the rate equation for the reaction
Determine the reaction rate if the concentration of A is 0
...
2 M

Ans
...
v1 = k[A]1x [B]1y
v2 = k[A]2x [B]2y

1
4

=(

1
2

x

)

x=2

b
...


c
...
v1 = k[A]1x [B]1y
1,25
...
(0,1)2
...
v = k [A]x [B]y = 1250 [A]2 [B]3
f
...
Indicate the reaction rate equation (in k) of the reaction
BrO3-(aq) + Br-(aq) + 6H+(aq)


...


v
1
152
2 1
76
1
4
19
1
19

time is inversely proportional to
speed, so: t =

8

𝟏
𝒗

v=

𝟏
𝒕

Ans
...
2z = 8
22
...
In the reaction A + B + C

D + E, obtained the following data:

 If the concentration A is fixed, the concentration of B and C each is
raised twice, then the reaction rate is twice as large as
...

 If the concentration of A and B each is raised twice, while the
concentration of C is fixed, the reaction rate is four times greater
...


v = k [A]x [B]y [C]z
[A]
1

a

2

a

3

2

4

[B]
2
2

2a

b
2b 𝟏
b

2a

𝟐

2

[C]

v

c

v

2c

2 2c

2b

2
2

c

We use the fast method:

1

2x
...
2z = 2

2y+z = 2

1

2x
...
(1)
y + z = 1…
...
(3)

We use the elimination method:
(2) y + z = 1

(1) x – y = 2

(3) x – z = 1 +
x + y = 2…
...
In the following, data from the results of the
2NO(g) + Br2(g)

2 NOBr(g) reaction rate experiment are given at

certain temperatures and pressures
...
Write down the rate equation for the reaction
...
If 4 mol of NO and Br2 are added to a room with a volume of 10 L, it
turns out that after 5 seconds 2 mol of NOBr gas is formed, then
determine:
i
...

ii
...

Ans
...
v = k [NO]x [Br2]y
We use the fast method:
2x = 2

x=1

v = k [NO]x [Br2]y

3x
...
(10-1)1 (10-1)2

3
...

2 NO + Br2
S
R
L

4
4
2  1
2
3

2 NOBr


2
2

Conclusion:
Average Reaction Rate

moles used: Moles Reacted

Instantaneous Reaction Rate

moles used: Leftovers Moles

Br2 moles reacted is 1
mole in 10 L

i)
ii) v = [NO] [Br2]2 =

𝟐
10


...
At some point in the reaction 2 A + B

C + D, [A] = 0,3629 M
...
What is the average rate of reaction
during this time interval?
Ans
...
Use data from table below to establish the order of reaction:
2 HgCl2(aq) + C2O42-(aq)

2 Cl-(aq) + 2 CO2(g) + Hg2Cl2(s)

with respect to HgCl2 dan C2O42- and also the overall order of the
reaction
...


v = k [HgCl2]m [C2O42-]n
We need to determine the values of m and n
...
Note also that R2 = 2 x R3
...

R2 = k x [HgCl2]2m x [C2O42-]2n = k x (2 x [HgCl2]3)m x [C2O42-]3n
R3 = k x [HgCl2]3m x [C2O42-]3n

2m = 2, so m = 1

To determine the value of n, we can form the ratio R2/R1
...
We have value m = 1
R2 = k x [HgCl2]21 x [C2O42-]2n = k x (0,105)1 x (2 x 0,15)n
R1 = k x [HgCl2]11 x [C2O42-]1n = k x (0,105)1 x (0,15)n

2n = 4, n = 2
First order in HgCl2 (m = 1), second order in C2O42- (n = 2) and third
order overall (m + n = 1 + 2 = 3)
...
The decomposition of hydrogen peroxide (H2O2) in water occurs
according to the reaction:
2 H2O2(aq)

2 H2O(l) + O2(g)

From 100 mL of H2O2 solution at a certain time it is observed that the
rate of formation of O2 gas is 4
...
4 L) at the same time the rate of
decomposition of H2O2 is
Ans
...
10-4 moles O2

Reaction rate:

Decomposition rate of H2O2 = 4

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