2025 RI Prelims H2 Chemistry P3 QP

© Raffles Institution 2025 9729/03/S/25 [Turn Over RAFFLES INSTITUTION 2025 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9729/03 Paper 3 Free Response 23 September 2025 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 page 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 30 printed pages and 2 blank pages.

2 © Raffles Institution 2025 9729/03/S/25 [Turn Over Section A Answer all the questions in this section. 1 This question is about ammonia, its application in space missions and its versatility in chemical reactions. (a) (i) State three basic assumptions of the kinetic theory as applied to an ideal gas. [2] (ii) Sketch a graph of pV/T against pressure, p, for 1 mole of an ideal gas. [1] (iii) On the same graph in (a)(ii), sketch and label the graph for 1 mole of NH3 gas. Explain the non-ideal behaviour of NH3 gas at moderately high pressure. [2] (iv) NH3 gas is contained in a 5 dm3 flask at a temperature of 27 C and a pressure of 4.00 atm. The gas is then compressed at constant temperature to half its volume and then heated to 227 C at constant volume. Calculate the final pressure of NH3 gas, in atm, in the container. [Assume NH3 gas behaves as an ideal gas under these conditions.] [2] ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2025 9729/03/S/25 [Turn Over 3 ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2025 9729/03/S/25 [Turn Over 4 (b) Ammonia has been proposed as an alternative zero-carbon fuel for use in space missions. The combustion of ammonia proceeds as follows. reaction 1 4NH3(g) + 3O2(g)  2N2(g) + 6H2O(l) ∆S = −583 J mol−1 K−1 The following data is given. Table 1.1 ∆ H / kJ mol−1 standard enthalpy change of formation of NH3(g) −46.1 standard enthalpy change of vaporisation of H2O(l) +44.0 (i) Define the term standard enthalpy change of combustion for ammonia gas. [1] (ii) Using the data in Table 1.1, together with data from the Data Booklet, construct an energy cycle to calculate a value for the standard enthalpy change of combustion, ∆Hc, of ammonia gas. [5] (iii) Suggest a reason why ∆S for reaction 1 is negative. [1] (iv) With reference to (b)(ii), calculate the standard Gibbs free energy change, ∆G, for reaction 1. Comment on the effect of temperature on the spontaneity of the reaction. [2] (v) Under high temperature conditions, the N2 gas produced in reaction 1 can undergo further reaction to produce oxides of nitrogen, NOx. Suggest a reason why lower temperatures do not favour the formation of NOx. [1] ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2025 9729/03/S/25 [Turn Over 5 ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2025 9729/03/S/25 [Turn Over 6 (c) The ammonia molecule can react in various ways: as an acid, as a base, as a nucleophile, as an oxidising agent and as a reducing agent. State the role of ammonia in each of the following reactions. Explain your answers briefly. [3] (i) NH3 + NaH  NaNH2 + H2 (ii) 2NH3 + NaOCl  N2H4 + NaCl + H2O (iii) (CH3)3CBr + NH3  (CH3)3CNH3+ + Br− ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………