Topic 16 – Kinetics II
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include investigating different methods for tracking rates of reaction by gas collection or change in mass or colour change, investigating
clock reactions such as Harcourt-Essen, using a simple rates experiment to calculate an activation energy. Mathematical skills that could be
developed in this topic include plotting and justifying the shapes of rate–concentration and concentration–time graphs, calculating half-life of a
reaction, calculating activation energy from a suitable graph, rearranging the Arrhenius equation in the form y = mx + c. Within this topic, students
can consider different methods used to measure reaction rates and collect valid data. Through the analysis of this data, and a knowledge of rate
equations, they can see how chemists are able to propose models to describe the mechanisms of chemical reactions.
1. understand the terms:
i rate of reaction // ii rate equation // iii order with respect to a substance in a rate equation
What is the definition of the term ‘rate of reaction’?
Rate of reaction refers to how fast the reaction progresses, or how fast the concentration of reactants
changes per unit time. Units = mol dm-3 s-1.
What is a rate equation?
A rate equation is something that links that rate of reaction to the concentration of reactants. It can
ONLY be deduced by doing an experiment.
What is ‘order’, when talking about rate equations?
‘Order’ refers to how changing the concentration of the reactant affects the rate of reaction. 0 th order
reactants do not affect the RR – 1st order affects it linearly, 2nd order affects it squared, etc…
iv overall order of reaction // v rate constant // vi half-life
What is meant by the ‘overall order of reaction’?
The overall order of reaction is the sum of the order of all the reactants.
What is the rate constant?
The rate constant, k, depends on the overall order of reaction. It is independent of the concentration or
time, but changes with temperature. The units of k are always one below the overall order of reaction.
Define ‘half-life’ in a Chemistry context.
Half-life is the time taken for the concentration of one of the reactants to fall by half.
vii rate-determining step // viii activation energy // ix heterogeneous and homogenous catalyst
What is the ‘rate-determining step’?
The RDS is the slowest step in a reaction mechanism. This is generally
responsible for the rate equation.
For example, if I walked from Torquay to Heathrow to catch a flight to New York, then the walking would
be the RDS. To speed up the whole process, it would make far more
, sense to get the train from Torquay to London than to take Concorde to New York – hence speeding up
the RDS is the best way to increase the rate of reaction.
Define ‘activation energy’.
Activation energy, EA, is the minimum energy required for a reaction (or step in a reaction) to occur.
What is the difference between a homogenous and heterogenous catalyst?
Homogenous catalysts are in the same state as the reaction that is being carried out. Heterogenous
catalysts are not – for example a catalytic converter in a car.
2. be able to determine and use rate equations of the form: rate = k[A] m[B]n, where m and n are 0, 1 or 2
Work out the units for the rate constant, and state the order with respect to each reactant and the whole
equation, for the rate equations (rate = k [S][E][G]2), (rate = k [T]) and (rate = k [D]2[C]).
Rate = k [S][E][G]2 k = mol-3dm9s-1 [S] = 1, [E] = 1, [G] = 2, [Total] = 4th
Rate = k [T] k = s-1 [T] = 1, [Total] = 1st
Rate = k [D]2[C] k = mol-2dm6s-1 [D] = 2, [C] = 1, [Total] = 3rd
Consider the reaction A + B + C --> D. The rate equation is (rate = k [B][C]2). Calculate how changing the
concentration affects the rate in each case.
R0 = 2.5moldm-3s-1 [A] x 3 R0 = 12moldm-3s-1 [C] x 10
No effect on rate of reaction. x100 RR, rate = 1200moldm-3s-1
R0 = 6.5moldm-3s-1 [B] x 2, [C] x 3 R0 = 12.5moldm-3s-1 [A] x 6, [B] / 4, [C] x 2
x2 AND x9, so x18, rate = 117moldm-3s-1 /4 AND x4, so no effect on rate of reaction.
3. be able to select and justify a suitable technique to obtain rate data for a given reaction, including:
i titration
The hydrolysis of bromobutane using hydroxide ions: C4H9Br + OH- -> C4H9OH + Br-.
The best technique to investigate the rate of this reaction is titration with standard acid solution.
ii colorimetry
Propanone reacts with iodine in acidic conditions as shown in the equation: CH 3COCH3 + I2 -> CH3COCH2I
+ H + + I -.
The most appropriate technique to investigate the rate of this reaction is colorimetry.
iii mass change
This decomposition: CaCO3 + 2HCl -> CaCl2 + H2O + CO2
You could either measure the mass loss due to CO2 escaping, or measure the volume of gas evolved.
Remember that this technique doesn’t always work if a gas is evolved, as it might be too light (e.g. H2).
iv volume of gas evolved
2
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include investigating different methods for tracking rates of reaction by gas collection or change in mass or colour change, investigating
clock reactions such as Harcourt-Essen, using a simple rates experiment to calculate an activation energy. Mathematical skills that could be
developed in this topic include plotting and justifying the shapes of rate–concentration and concentration–time graphs, calculating half-life of a
reaction, calculating activation energy from a suitable graph, rearranging the Arrhenius equation in the form y = mx + c. Within this topic, students
can consider different methods used to measure reaction rates and collect valid data. Through the analysis of this data, and a knowledge of rate
equations, they can see how chemists are able to propose models to describe the mechanisms of chemical reactions.
1. understand the terms:
i rate of reaction // ii rate equation // iii order with respect to a substance in a rate equation
What is the definition of the term ‘rate of reaction’?
Rate of reaction refers to how fast the reaction progresses, or how fast the concentration of reactants
changes per unit time. Units = mol dm-3 s-1.
What is a rate equation?
A rate equation is something that links that rate of reaction to the concentration of reactants. It can
ONLY be deduced by doing an experiment.
What is ‘order’, when talking about rate equations?
‘Order’ refers to how changing the concentration of the reactant affects the rate of reaction. 0 th order
reactants do not affect the RR – 1st order affects it linearly, 2nd order affects it squared, etc…
iv overall order of reaction // v rate constant // vi half-life
What is meant by the ‘overall order of reaction’?
The overall order of reaction is the sum of the order of all the reactants.
What is the rate constant?
The rate constant, k, depends on the overall order of reaction. It is independent of the concentration or
time, but changes with temperature. The units of k are always one below the overall order of reaction.
Define ‘half-life’ in a Chemistry context.
Half-life is the time taken for the concentration of one of the reactants to fall by half.
vii rate-determining step // viii activation energy // ix heterogeneous and homogenous catalyst
What is the ‘rate-determining step’?
The RDS is the slowest step in a reaction mechanism. This is generally
responsible for the rate equation.
For example, if I walked from Torquay to Heathrow to catch a flight to New York, then the walking would
be the RDS. To speed up the whole process, it would make far more
, sense to get the train from Torquay to London than to take Concorde to New York – hence speeding up
the RDS is the best way to increase the rate of reaction.
Define ‘activation energy’.
Activation energy, EA, is the minimum energy required for a reaction (or step in a reaction) to occur.
What is the difference between a homogenous and heterogenous catalyst?
Homogenous catalysts are in the same state as the reaction that is being carried out. Heterogenous
catalysts are not – for example a catalytic converter in a car.
2. be able to determine and use rate equations of the form: rate = k[A] m[B]n, where m and n are 0, 1 or 2
Work out the units for the rate constant, and state the order with respect to each reactant and the whole
equation, for the rate equations (rate = k [S][E][G]2), (rate = k [T]) and (rate = k [D]2[C]).
Rate = k [S][E][G]2 k = mol-3dm9s-1 [S] = 1, [E] = 1, [G] = 2, [Total] = 4th
Rate = k [T] k = s-1 [T] = 1, [Total] = 1st
Rate = k [D]2[C] k = mol-2dm6s-1 [D] = 2, [C] = 1, [Total] = 3rd
Consider the reaction A + B + C --> D. The rate equation is (rate = k [B][C]2). Calculate how changing the
concentration affects the rate in each case.
R0 = 2.5moldm-3s-1 [A] x 3 R0 = 12moldm-3s-1 [C] x 10
No effect on rate of reaction. x100 RR, rate = 1200moldm-3s-1
R0 = 6.5moldm-3s-1 [B] x 2, [C] x 3 R0 = 12.5moldm-3s-1 [A] x 6, [B] / 4, [C] x 2
x2 AND x9, so x18, rate = 117moldm-3s-1 /4 AND x4, so no effect on rate of reaction.
3. be able to select and justify a suitable technique to obtain rate data for a given reaction, including:
i titration
The hydrolysis of bromobutane using hydroxide ions: C4H9Br + OH- -> C4H9OH + Br-.
The best technique to investigate the rate of this reaction is titration with standard acid solution.
ii colorimetry
Propanone reacts with iodine in acidic conditions as shown in the equation: CH 3COCH3 + I2 -> CH3COCH2I
+ H + + I -.
The most appropriate technique to investigate the rate of this reaction is colorimetry.
iii mass change
This decomposition: CaCO3 + 2HCl -> CaCl2 + H2O + CO2
You could either measure the mass loss due to CO2 escaping, or measure the volume of gas evolved.
Remember that this technique doesn’t always work if a gas is evolved, as it might be too light (e.g. H2).
iv volume of gas evolved
2
