RI Kinetics Remedial

Name: ………………………………………. ( ) Class: ……………. Date: ……………. Raffles Institution Year 6 H2 Chemistry 2025 Set A T2W3 – Kinetics Notes: overall order of reaction rate equation units of k rate- [reactant] graph [reactant]- time graph half-life (circle) zero rate = k constant / not constant one rate = k[A] constant / not constant two rate = k[A]2 constant / not constant rate [A]0 [A] time0 rate [A]0 [A] time0 rate [A]0 [A] time0  Pre-ChemFocus Activity  • Revise key concepts in Kinetics: half-life, “clock” and continuous experiments. • To view infopack at IVY > C2025 – H2 CHEMISTRY > Pages > [ChemFocus] Y6 T2W3 Kinetics (and Y5 T3W9, if needed) > FIRST VIDEO ONLY

Self-Check Questions 1 The diagram shows the energy profile of a reaction that occurs with and without a catalyst. Which of the following can be deduced from the diagram? A E4 is the . B The forward catalysed reaction is endothermic. C The enthalpy change of reaction is (E2 – E3). D The enthalpy change of reaction is decreased by using a catalyst. 2 Which changes would cause both of the rate constants k1 and k–1 to be increased? 1 introducing a catalyst 2 heating the equilibrium mixture 3 increasing the concentrations of the reactants A 1 , 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only Check your answers at IVY > C2025 – H2 CHEMISTRY > Pages > [ChemFocus] Y6 T2W3 Kinetics > Remaining videos

3 A chemical plant illegally dumped some radioactive waste in a landfill. This waste contains two radioactive isotopes M and N. The half-life of M is 3 days whereas that of N is 2 days. The authorities found out about this illegal dumping only when the waste had been in the landfill for 12 days. They did an immediate analysis on a sample of the waste and found equal amounts of M and N. Considering that the decay of radioactive isotopes follows first-order kinetics, what is the molar ratio of M to N if the waste had been in the landfill for 6 days? M : N A 1 : 4 B 1 : 2 C 2 : 1 D 4 : 1 4 The reaction between potassium manganate(VII) and ethanedioic acid is an example of auto-catalytic reactions, in which one of the products catalyses the reaction. 2MnO4–(aq) + 5H2C2O4(aq) + 6H3O+(aq) → 2Mn2+(aq) + 10CO2(g) + 14H2O(l) Which graph correctly represents the kinetics of this reaction?

Tutorial Discussion Questions (to complete before Chemfocus session) 1a [modified NYJC 2018/I/9] The decomposition of hydrogen peroxide follows first order kinetics. 2H2O2 ⟶ 2H2O + O2 A certain solution of hydrogen peroxide undergoes complete decomposition to liberate 96 cm3 of oxygen gas. It is found that at 20 °C, 48 cm3 of oxygen was collected in 35 min. Use the following equation, how long will it take for 80 cm3 of the gas to be produced? (H2O2)t (H2O2)0 = �1 2� n where: (H2O2)0 is the amount of H2O2 when time = 0, (H2O2)t is the amount of H2O2 left at time, t, n is the number of half-lives elapsed. A 87.5 min B 90.5 min C 97.5 min D 105 min

2a [N2013/3/5(c),(d)] The Harcourt and Esson reaction is that between hydrogen peroxide and acidified potassium iodide. The rate of reaction can be followed by measuring the amount of iodine produced after various times, from which the concentration of H 2O2 remaining can be calculated. The following reaction mixture was prepared for experiment 1. initial [H+] = 0.200 mol dm–3 initial [I–] = 0.200mol dm–3 initial [H2O2] = 0.0200 mol dm–3 The following table shows [H2O2] at various times. time /s [H2O2] /mol dm–3 0 0.0200 80 0.0167 183 0.0135 315 0.0103 490 0.0071 760 0.0039 (i) Plot these data on suitable axes below. [2]

(ii) Use your graph to determine (1) the order of reaction with respect to [H2O2], (2) the initial rate, in mol dm–3 s–1, showing all your working and drawing clearly any construction lines on your graph. [4] Further experiments were carried out changing [H+] and [I–], but keeping the initial [H2O2] the same as before. The following results were obtained. experiment initial [H+] /mol dm–3 initial [I–] /mol dm–3 initial rate /mol dm–3 s–1 2 0.400 0.200 8.4 × 10–5 3 0.300 0.200 6.3 × 10–5 4 0.200 0.100 2.1 × 10–5 (iii) Determine the orders with respect to [H+] and [I–]. Explain your reasoning. [2] (iv) Hence, write the rate equation for the reaction, and calculate a value for the rate constant. Include units in your answer. [2]

Tutorial Practice Questions (to be attempted IN CLASS) 1b [N2020/1/13] Hydrogen peroxide solution decomposes. The equation for this reaction is shown. 2H2O2(aq) → 2H2O(l) + O2(g) A 200 cm3 sample of hydrogen peroxide solution is warmed. After 120 minutes, 6.00 dm3 of oxygen gas, measured at r.t.p., is collected. Under these conditions, the reaction has a constant half-life of 40 minutes. What is the initial concentration of the hydrogen peroxide solution? A 0.57 mol dm–3 B 1.4 mol dm–3 C 2.5 mol dm–3 D 2.9 mol dm–3

2b [RI 2022 Prelim P2 Q2(b)] Nitrogen dioxide undergoes the following gas phase reaction with hydrogen chloride, as shown in equation 1.1. equation 1.1 2NO2(g) + HCl(g) → NOCl(g) + HNO3(g) To study the kinetics for this reaction, three separate experiments were carried out in a vessel of fixed volume at a constant temperature of 500 K. The initial concentrations of NO2 and HCl are shown in Table 1.1. Table 1.1 experiment initial [NO2] / mol dm−3 initial [HCl] / mol dm−3 1 1.00 0.05 2 0.50 0.05 3 0.50 0.01 To monitor the progress of the reaction for each experiment, the total pressure in the vessel was measured at regular time intervals and the corresponding concentrations of NOCl were calculated. Fig. 1.1 shows how the concentration of NOCl varies with time for experiments 1 and 2. time / s Fig. 1.1 0 0.01 0.02 0.03 0.04 0.05 0 50 100 150 200 250 300 [NOCl] / mol dm−3 experiment 1 experiment 2

(i) Using Fig. 1.1, determine the initial rate of reaction for experiments 1 and 2, showing your working clearly on the graph. Hence, deduce the order of reaction with respect to NO2. [4] (ii) State the final concentration of NOCl in the vessel for experiment 1 if the reaction were to proceed to completion. …………………………………………………………………………………………..[1] (iii) Hence, determine the order of reaction with respect to HCl. Show your working, including construction lines on Fig. 1.1. [2] (iv) Using your answer in (iii), predict the half-lives of experiments 2 and 3, giving your reasoning. [2]

Self-Check Answers 1 Answer: C. Option A is wrong because E4 is the activation energy for the reverse uncatalysed reaction since the activation energy of the forward reaction is higher. Option B is wrong because in the forward reaction, the products have lower energy than the reactants. Hence, the forward reaction is exothermic. Option D is wrong because a catalyst has no effect on the enthalpy change of reaction. 2 Answer: B. Option 1 is correct because a catalyst lowers the activation energy of both the forward and reverse reaction by the same amount, causes both k1 and k–1 to increase. (𝑘𝑘 = 𝐴𝐴𝑒𝑒 −𝐸𝐸𝑎𝑎 𝑅𝑅𝑅𝑅 ) Option 2 is correct because heating the equilibrium mixture would increase the rate of both forward and reverse reaction, causing both k1 and k–1 to increase. Option 3 is wrong because concentration has no effect on the rate constant of the reaction. 3 Answer: B After 12 days, there were equal amounts of M and N. We can assume that there is 1 mol of M and 1 mol of N after 12 days. M has a half-