A Level Chemistry (A2) chapter 4: Reaction kinetics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
50 exam-style questions on Reaction kinetics, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Simple rate equations, orders of reaction and rate constants26 questions
Homogeneous and heterogeneous catalysts24 questions
Ten Reaction kinetics questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A graph of initial rate (y-axis) against [B] (x-axis) is a straight line through the origin. What is the order of reaction with respect to B?
A
zero
B
first
C
second
D
it cannot be found from this graph
Show answer
Answer: B. Rate proportional to [B] means rate = k[B]1. On a rate–concentration graph a zero-order reactant gives a horizontal line, and a second-order reactant gives an upward curve through the origin.
2. Fe2+ ions catalyse the reaction S2O82− + 2I− → 2SO42− + I2. Which pair of equations shows how?
Answer: C. Fe2+ is oxidised by peroxodisulfate to Fe3+, which then oxidises iodide ions and is reduced back to Fe2+. Each step is between oppositely charged ions. The version with a single Fe2+ does not balance for charge.
3. In a catalytic converter: 2CO(g) + 2NO(g) → 2CO2(g) + N2(g). Which statement is correct?
A
NO is oxidised and the oxidation number of N changes from +2 to 0
B
CO is reduced and the oxidation number of C changes from +2 to +4
C
NO is reduced and the oxidation number of N changes from +2 to 0
D
NO is reduced and the oxidation number of N changes from +4 to 0
Show answer
Answer: C. In NO, N is +2; in N2 it is 0, a decrease, so NO is reduced. C goes from +2 in CO to +4 in CO2, which is oxidation.
4. A reaction is first order in A and zero order in all other reactants. When [A] = 0.050 mol dm−3 the initial rate is 2.4 × 10−4 mol dm−3 s−1. What is the half-life of A?
A
72 s
B
144 s
C
208 s
D
2890 s
Show answer
Answer: B. k = 2.4 × 10−4 / 0.050 = 4.8 × 10−3 s−1; t½ = 0.693 / k = 144 s. 208 s is 1 / k; 2890 s divides 0.693 by the rate instead of k.
5. For a reaction, a graph of [A] against time is a straight line with a negative gradient until A is used up. What is the order of reaction with respect to A?
A
first
B
second
C
zero
D
third
Show answer
Answer: C. A constant gradient means the rate stays the same as [A] falls, so the rate does not depend on [A]: zero order. A first-order reaction gives a curve with a constant half-life.
6. Which pair of catalysts are BOTH homogeneous in the reactions named?
A
H+(aq) in the hydrolysis of an ester, and Fe2+(aq) in the reaction of S2O82− with I−
B
platinum in a catalytic converter, and NO2 in the atmospheric oxidation of SO2
C
iron in the Haber process, and nickel in the hydrogenation of alkenes
D
Fe2+(aq) in the reaction of S2O82− with I−, and iron in the Haber process
Show answer
Answer: A. Aqueous H+ and Fe2+ are in the same phase as their aqueous reactants. Iron, nickel and platinum are solids catalysing gas (or liquid) reactions, so they are heterogeneous.
7. On a concentration–time graph for reactant R, [R] falls from 0.60 to 0.30 mol dm−3 in 40 s and from 0.30 to 0.15 mol dm−3 in the next 40 s. What does this show?
A
the reaction is zero order with respect to R
B
the reaction is second order with respect to R
C
the rate of reaction stays constant
D
the reaction is first order with respect to R
Show answer
Answer: D. Successive half-lives are equal (40 s). A half-life that does not depend on concentration is the mark of a first-order reaction. For a second-order reaction each half-life would be twice as long as the one before.
8. E⦵ values: S2O82−/SO42− +2.01 V; Fe3+/Fe2+ +0.77 V; I2/I− +0.54 V. Why can either Fe2+ or Fe3+ ions catalyse the reaction between S2O82− and I−?
A
E⦵(Fe3+/Fe2+) is more positive than both, so Fe3+ oxidises both reactants
B
E⦵(Fe3+/Fe2+) is less positive than both, so Fe2+ reduces both reactants
C
E⦵(Fe3+/Fe2+) lies between the other two, so both catalysed steps are feasible
D
iron is a transition element, so its ions can catalyse any redox reaction
Show answer
Answer: C. Fe2+ can be oxidised by S2O82− (2.01 − 0.77 = +1.24 V) and Fe3+ can oxidise I− (0.77 − 0.54 = +0.23 V). Whichever iron ion is added, the cycle starts with the step that ion takes part in.
9. For a reaction between C and D, doubling [C] while keeping [D] constant doubles the rate. Doubling both [C] and [D] at the same time makes the rate eight times faster. What is the rate equation?
A
rate = k[C]2[D]
B
rate = k[C][D]
C
rate = k[C][D]2
D
rate = k[C]2[D]2
Show answer
Answer: C. Doubling [C] alone doubles the rate, so the reaction is first order in C. Doubling both gives ×8 = ×2 (from C) × ×4, so doubling [D] alone would quadruple the rate: second order in D. rate = k[C]2[D] also gives ×8 overall but contradicts the first result.
10. Potassium manganate(VII) reacts with ethanedioate ions in acid. The purple colour fades slowly at first, then faster, then slowly again as the reactants run out. Which explanation fits?
A
the reaction is exothermic, so it gets faster only because the mixture warms up
B
a product, Mn2+(aq), acts as a homogeneous catalyst for the reaction
C
the solid MnO2 formed acts as a heterogeneous catalyst
D
the concentration of manganate(VII) rises during the reaction
Show answer
Answer: B. Mn2+ is formed by the reaction and catalyses it in the same aqueous phase (autocatalysis), so the rate rises as Mn2+ builds up and then falls as the reactants are used up.
50, each with the answer and a short explanation, across 2 topics: Simple rate equations, orders of reaction and rate constants, Homogeneous and heterogeneous catalysts. Every chapter test draws ten of them, so you can take it many times.
Is the A Level Chemistry (A2) chapter 4 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
