Reaction kinetics — AS & A Level Chemistry (9701) questions by topic
Rate equations, Boltzmann distributions and titration practicals combine here: interpreting equilibrium mixtures in the Haber process, comparing catalysed and uncatalysed activation energies on a Boltzmann curve, and calculating gas volumes from a hydrogen peroxide decomposition.
Deduce, calculate, explain, identify and state are the leading command words across 52 questions from 2023 to 2025 papers, spanning 1 to 16 marks, with graphical and rate-determining-step reasoning both tested heavily. Submitting titration and graph-plotting answers for instant marking catches a line drawn from first point to last instead of a true best fit, or three decimal places mistaken for three significant figures, before it costs marks across the whole practical.
What examiners look for
- Examiners repeatedly note candidates confusing significant figures with decimal places, recording table values to three decimal places rather than three significant figures.
- A common mistake was drawing a line from the first point to the last point rather than a true line of best fit.
- Reports flag stating 'repeat and average' alone as insufficient, and transferring solution to a volumetric flask without rinsing the beaker as a technique error.
- Strong scripts dissolved the solid in a small volume of water, transferred it to a 250 cm3 volumetric flask, rinsed the beaker into the flask, and made up to the mark.
- Candidates who recognised that order and the rate equation can only be determined experimentally, and that not every reactant need feature in the rate-determining step, scored well.
May–June 2025, Paper 11
The rate of the reaction between a reactive metal and an excess of a dilute acid is investigated. The total volume of hydrogen gas produced is recorded every 30 seconds for 3…
Answer this question and get it marked →In the diagram, curve X was obtained by measuring the volume of oxygen produced during the decomposition of 100 cm^3 of 1.0 mol dm^-3 hydrogen peroxide. A catalyst of…
Answer this question and get it marked →May–June 2025, Paper 12
The diagram shows a Boltzmann distribution of molecular energies for a gaseous reaction at two different temperatures and two different activation energies (T1, T2, EA(1), EA(2)).…
Answer this question and get it marked →Aqueous hydrogen peroxide, H2O2, decomposes into water and oxygen in the presence of a suitable catalyst. 50 cm^3 of a 0.50 mol dm^-3 solution of hydrogen peroxide produced 120…
Answer this question and get it marked →May–June 2025, Paper 13
Diagram 1 shows the reaction pathway for a reaction. Diagram 2 shows a graph of concentration of reactant against time for the same reaction. The reaction is exothermic with…
Answer this question and get it marked →The gaseous compound Z decomposes on heating. In the diagram, Boltzmann distributions for Z at two different temperatures, P and Q, are shown. Lines X and Y indicate activation…
Answer this question and get it marked →May–June 2025, Paper 14
The distribution of molecular energies in an ideal gas can be represented in a Boltzmann distribution. Which change in conditions leads to a larger value for the number of…
Answer this question and get it marked →Propyl methanoate is hydrolysed with NaOH(aq) at 20 °C to form two products, X and Y. Product X is an alcohol. Data from the experiment is shown (table of time/s vs [X]/mol…
Answer this question and get it marked →May–June 2025, Paper 21
(i) On the axes of Fig. 3.1, sketch the Boltzmann distribution of molecular energies for H2 at a higher temperature than T. (ii) Explain why increasing temperature increases the…
Answer this question and get it marked →May–June 2025, Paper 23
(i) Use Fig. 4.1 to find the average rate of change of concentration of HCl(aq) in this reaction between 0–100 seconds and between 400–500 seconds. Include units in your answers.…
Answer this question and get it marked →May–June 2025, Paper 41
Three experiments are carried out to investigate the reaction of nitrogen oxide, NO, with chlorine. 2NO + Cl2 → 2NOCl The rate equation for this reaction is: rate = k[NO]2[Cl2]…
Answer this question and get it marked →May–June 2025, Paper 42
H2O2 oxidises I⁻ ions in acidic solution. H2O2 + 2I⁻ + 2H⁺ → I2 + 2H2O The initial rate of reaction was measured for different initial concentrations of H2O2 and I⁻. The results…
Answer this question and get it marked →May–June 2025, Paper 43
Three experiments are carried out to investigate the reaction of nitrogen oxide, NO, with chlorine. 2NO + Cl2 → 2NOCl The rate equation for this reaction is: rate = k[NO]²[Cl2]…
Answer this question and get it marked →May–June 2025, Paper 51
An experiment is carried out to determine the rate constant, k, for the hydrolysis of ethyl ethanoate, CH₃COOC₂H₅, using a hydrochloric acid, HCl(aq), catalyst. The equation:…
Answer this question and get it marked →May–June 2025, Paper 53
An experiment is carried out to determine the rate constant, k, for the hydrolysis of ethyl ethanoate, CH₃COOC₂H₅, using a hydrochloric acid, HCl(aq), catalyst. The equation:…
Answer this question and get it marked →May–June 2024, Paper 11
The Boltzmann distribution for the hydrogenation of an alkene at a particular temperature in the absence of a catalyst is shown, with the activation energy Ea marked on the energy…
Answer this question and get it marked →May–June 2024, Paper 12
The volume of ammonia produced against time is measured in two experiments. N2(g) + 3H2(g) <= 2NH3(g) deltaH = -92 kJ mol^-1 In experiment 1, 3 mol of H2(g) and 1 mol of N2(g)…
Answer this question and get it marked →Gas Q decomposes slowly at room temperature. Q(g) - X(g) + Z(g) The Boltzmann distribution curve for gas Q at room temperature is shown, with the activation energy Ea marked on…
Answer this question and get it marked →May–June 2024, Paper 13
In the diagram, X is the Boltzmann distribution for the energies of the particles in a reaction and Ea1 is the activation energy for that reaction. Three Boltzmann distribution…
Answer this question and get it marked →May–June 2024, Paper 23
N2(g) reacts with H2(g) in the Haber process, as shown in reaction 1. reaction 1: N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = −x kJ mol⁻¹ Table 2.1 shows the different conditions used to…
Answer this question and get it marked →May–June 2024, Paper 41
In aqueous solution, persulfate ions, S2O8^2-, react with iodide ions, as shown in reaction 1: S2O8^2- + 2I- - 2SO4^2- + I2. The rate of reaction 1 is investigated. A sample of…
Answer this question and get it marked →May–June 2024, Paper 42
Nitrosyl chloride, NOCl, can be formed by the reaction between nitrogen monoxide and chlorine: 2NO + Cl2 - 2NOCl. The initial rate of this reaction is investigated, starting with…
Answer this question and get it marked →May–June 2024, Paper 43
In aqueous solution, persulfate ions, S2O8^2-, react with iodide ions, as shown in reaction 1: S2O8^2- + 2I- - 2SO4^2- + I2. The rate of reaction 1 is investigated. A sample of…
Answer this question and get it marked →October–November 2024, Paper 11
In acidic conditions, iodine reacts with propanone in a substitution reaction. CH₃COCH₃(aq) + I₂(aq) → CH₃COCH₂I(aq) + HI(aq) The kinetics of the reaction are investigated using a…
Answer this question and get it marked →The diagram shows a Boltzmann distribution curve. The axes are not labelled. The curve rises from the origin to a peak and then falls away towards higher energy. Point Y is marked…
Answer this question and get it marked →October–November 2024, Paper 12
Why does the rate of a gaseous reaction increase when the pressure is increased at a constant temperature? A More particles have energy that exceeds the activation energy. B The…
Answer this question and get it marked →The Boltzmann distribution for a mixture of gases capable of reaction is shown. The two curves represent the mixture of gases at 25 °C and at 35 °C. The activation energies for…
Answer this question and get it marked →October–November 2024, Paper 13
In acidic conditions, iodine reacts with propanone in a substitution reaction. CH₃COCH₃(aq) + I₂(aq) → CH₃COCH₂I(aq) + HI(aq) The kinetics of the reaction are investigated using a…
Answer this question and get it marked →The diagram shows a Boltzmann distribution curve. The axes are not labelled. The curve rises from the origin to a peak and then falls away towards higher energy. Point Y is marked…
Answer this question and get it marked →October–November 2024, Paper 41
(a) A and B react together to give product AB. A + B - AB When the concentrations of A and B are both 0.0100 mol dm-3, the rate of formation of AB is 7.62 x 10^-4 mol dm-3 s-1.…
Answer this question and get it marked →October–November 2024, Paper 42
(a) The equation for reaction 1 is shown. reaction 1: X - 2Y Reaction 1 is first order with respect to the concentration of X. The half-life of the reaction, t1/2, is 900 s at 20…
Answer this question and get it marked →October–November 2024, Paper 43
(a) A and B react together to give product AB. A + B - AB When the concentrations of A and B are both 0.0100 mol dm-3, the rate of formation of AB is 7.62 x 10^-4 mol dm-3 s-1.…
Answer this question and get it marked →February–March 2023, Paper 12
The diagram shows the Boltzmann distribution for one mole of a gas. The gas takes part in a reaction with an activation energy, Ea. The graph plots 'number of particles with…
Answer this question and get it marked →A student carries out four experiments to investigate the rate of reaction between 3.0 g of calcium carbonate and hydrochloric acid. CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) +…
Answer this question and get it marked →February–March 2023, Paper 52
A second student looked at the equation for reaction 1 and stated the order with respect to [I⁻(aq)] must be second order because the balanced equation contains 2I⁻(aq). Suggest…
Answer this question and get it marked →May–June 2023, Paper 11
Iodine and propanone react according to the following equation. I2(aq) + CH3COCH3(aq) → CH3COCH2I(aq) + HI(aq) If the concentration of propanone is increased, keeping the total…
Answer this question and get it marked →The temperature of a sample of an inert gas is increased. What effect does this have on the number of molecules with the most probable energy and on the number of molecules with…
Answer this question and get it marked →May–June 2023, Paper 12
The equations for two reactions are shown. reaction X: 2NOBr - 2NO + Br2 reaction Y: 2NOCl - 2NO + Cl2 The two reactions have similar reaction mechanisms. The initial rate of…
Answer this question and get it marked →The diagram shows the Boltzmann distribution of energies in a gas. The gas can take part in a reaction with an activation energy, Ea. The gas is maintained at a constant…
Answer this question and get it marked →May–June 2023, Paper 13
The rate of an exothermic reaction is followed by measuring the concentration of a reactant at regular time intervals. During the experiment the temperature of the reaction…
Answer this question and get it marked →For a particular reversible reaction the backward reaction is endothermic. The activation energy of the backward reaction is 160 kJ mol^-1. It can be assumed that the backward…
Answer this question and get it marked →The diagram shows the Boltzmann distribution of the energy of gaseous molecules at a particular temperature. The distribution rises from the origin to a peak labelled Y and then…
Answer this question and get it marked →May–June 2023, Paper 41
Aqueous acidified iodate(V) ions, IO₃⁻, react with iodide ions: IO₃⁻ + 6H⁺ + 5I⁻ → 3I₂ + 3H₂O. The initial rate of this reaction is investigated; Table 3.1 gives the results. The…
Answer this question and get it marked →The exhaust systems of most modern gasoline-fuelled cars contain a catalytic converter with three metal catalysts. These metals act as heterogeneous catalysts. Name three metal…
Answer this question and get it marked →May–June 2023, Paper 42
In aqueous solution, iron(III) ions react with iodide ions: 2Fe³⁺ + 2I⁻ → 2Fe²⁺ + I₂. A series of experiments is carried out using different concentrations of Fe³⁺ and I⁻, as…
Answer this question and get it marked →May–June 2023, Paper 43
Aqueous acidified iodate(V) ions, IO3-, react with iodide ions, as shown: IO3- + 6H+ + 5I- - 3I2 + 3H2O. The initial rate of this reaction is investigated. Table 3.1 gives…
Answer this question and get it marked →October–November 2023, Paper 11
In reaction 1, a student measures the initial rate of production of CO2(g) when CuCO3(s) is added to 50 cm3 of 0.1 mol dm-3 HNO3(aq). In reaction 2, the student repeats the…
Answer this question and get it marked →The forward reaction of a reversible reaction is exothermic and has an activation energy of +30 kJ mol-1. The reverse reaction proceeds by a mechanism that is the exact reverse of…
Answer this question and get it marked →October–November 2023, Paper 12
The decomposition of hydrogen peroxide in the presence of MnO2 produces water and oxygen gas: 2H2O2(aq) - 2H2O(l) + O2(g). The volume of gas collected when 0.2 g of MnO2 is added…
Answer this question and get it marked →October–November 2023, Paper 13
In reaction 1, a student measures the initial rate of production of CO2(g) when CuCO3(s) is added to 50 cm3 of 0.1 mol dm^-3 HNO3(aq). In reaction 2, the student repeats the…
Answer this question and get it marked →The forward reaction of a reversible reaction is exothermic and has an activation energy of +30 kJ mol^-1. The reverse reaction proceeds by a mechanism that is the exact reverse…
Answer this question and get it marked →October–November 2023, Paper 42
Propanone, CH₃COCH₃, reacts with iodine, I₂, in the presence of an acid catalyst: CH₃COCH₃ + I₂ → CH₃COCH₂I + H⁺ + I⁻. The rate equation for this reaction is rate =…
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