2024 JPJC Chem Prelim P3 solutions

© Jurong Pioneer Junior College [Turn Over NAME CLASS 23S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2024 CHEMISTRY 9729/03 Higher 2 Paper 3 Free Response Questions 12 September 2024 2 hours Candidates answer on the Question paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a HB pencil for any diagrams, 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. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. 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 1 2 3 4 or 5 Penalty (delete accordingly) Lack 3sf in final answer –1 / NA Missing/wrong units in final ans –1 / NA Bond linkages –1 / NA Total 80 This document consists of 32 printed pages.

2 © Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2024 Section A Answer all the questions in this section. 1 (a) One version of the Fischer-Tropsch process for manufacturing methane is the reaction of carbon monoxide with hydrogen. CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g) H210 kJ mol-1 A mixture of CO and H2 in a 1:3 molar ratio was introduced into a sealed vessel and heated to 1200K. At equilibrium, 40% of the CO ha d reacted. The total pressure in the vessel was 12 atm at equilibrium. For Examiner’s Use (i) Write an expression for the equilibrium constant, Kp for this reaction. ( )  =  24 2 HO C H p 3 CO H pp pp K [1] Examiner’s comments: This was generally well answered. Common mistakes: • Excluding partial pressure of water in the expression. • Using [ ] (ii) Use your expression to calculate the value of Kp for the reaction at 1200K. Include its units. 3H2(g) + CO(g)  CH4(g) +H2O (g) Initial amount/mol 3x x − - Change/mol −3(0.4) x −0.4 x + (0.4) x + (0.4) x Equilibrium amount/mol 1.8x 0.6 x 0.4 x 0.4x Total amount at equilibrium = 1.8x + 0.6x + 0.8x = 3.2x 2HP = 121.8x×3.2x = 6.75 atm COP = 0.6x×123.2x = 2.25 atm 4CHP=2HOP = 40. x×123.2x = 1.5 atm ( ) ( )( )= 2 p 3 1.50 6.75 2.25 K = 0.00325 atm−2 [3] Examiner’s comments: This was generally well answered. Most students wer