2024 RI Prelim H2 Chem Paper 3 QP Final

© Raffles Institution 2024 9729/03/S/24 [Turn Over RAFFLES INSTITUTION 2024 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9729/03 Paper 3 Free Response 17 September 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A Section B Total 1 / 20 (Circle the question you have answered) / 80 2 / 20 4 / 20 3 / 20 5 / 20 This document consists of 29 printed pages and 3 blank pages.

2 © Raffles Institution 2024 9729/03/S/24 [Turn Over Section A Answer all the questions in this section. 1 Contrails are the visible clouds that form in a line behind an aircraft during its flight. (a) One of the reactions involved in the formation of contrails is shown in equation 1. equation 1 2SO2 + O2 ⇌ 2SO3 ∆Hr < 0 (i) Write the expression for the equilibrium constant, Kc, for equation 1, stating its units. [1] (ii) At 450 °C, a sealed 1.00 dm3 flask is found to contain an equilibrium mixture of gases as shown in Table 1.1. Table 1.1 SO2 O2 SO3 amount / mol 0.500 0.100 4.60 Use these data to calculate Kc for the reaction in equation 1. [2] (iii) Using information from (a)(ii), calculate the total pressure, in MPa, of the gaseous mixture at equilibrium. Assume that the gases behave ideally. [1 MPa = 106 Pa] [1] (iv) Hence, calculate the equilibrium partial pressure, in MPa, of SO3. [1] (v) Calculate the amount of oxygen that must be added to the mixture to increase the amount of SO3, at equilibrium, to 4.70 mol at the same temperature. [2] ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2024 9729/03/S/24 [Turn Over 3 ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2024 9729/03/S/24 [Turn Over 4 (b) Another sealed flask contains the same gaseous mixture in equation 1. (i) Explain how an increase in temperature affects the equilibrium amount of SO2. [2] (ii) The system is initially at equilibrium at t = 0 s. At time = t 1, the temperature of the system increases sharply. Equilibrium is re-established at time = t2. Sketch a labelled graph of both the forward and backward rates of the reaction against time. You may use f and b to label the forward and backward rates respectively. [2] ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2024 9729/03/S/24 [Turn Over 5 BLANK PAGE

© Raffles Institution 2024 9729/03/S/24 [Turn Over 6 (c) Contrail formation depends on the proportion of H2SO4 produced in the exhaust gases of an airplane. The reactions to produce H2SO4 are shown below. reaction 1 SO2(g) + •OH(g) ⇌ HOSO2(g) reaction 2 HOSO2(g) + O2(g) ⇌ HO2(g) + SO3(g) reaction 3 SO 3(g) + H2O(g) ⇌ H2SO4(g) The higher the proportion of H2SO4, the more contrails are formed. Fig. 1.1 shows how ∆Gr for reaction 1 varies with temperature, T, of the exhaust gases. Fig. 1.1 Fig. 1.1 (i) State the minimum temperature at which reaction 1 is no longer spontaneous. [1] (ii) Explain, in terms of position of equilibrium, the effect of increasing temperature on the proportion of H2SO4 produced in the exhaust gases. [2] -100 -80 -60 -40 -20 0 20 40 60 ∆Gr  / kJ mol−1 T / K • • • 200 400 600 800 1000 1200

© Raffles Institution 2024 9729/03/S/24 [Turn Over 7 ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………. (d) (i) State two basic assumptions of the kinetic theory as applied to an ideal gas. [2] (ii) Explain why a gas deviates from ideal behaviour at high pressure. [1] ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….