2025 H2 Chem Prelim P2 QP_CJC

[Turn over 9729/02 CJC JC2 Preliminary Examination 2025 CANDIDATE NAME CLASS 2T INDEX NUMBER CHEMISTRY 9729/02 Paper 2 Structured Questions 29 August 2025 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. 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. The use of an approved scientific calculat or is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 21 printed pages and 1 blank page. For Examiner’s Use Paper 1 30 Paper 2 Q1 /16 Q2 / 7 Q3 /10 Q4 /18 Q5 /13 Q6 /11 75 Paper 3 80 Paper 4 55 OVERALL (100%) GRADE Catholic Junior College JC2 Preliminary Examination Higher 2

2 9729/02 CJC JC2 Preliminary Examination 2025 Answer all the questions in the space provided. 1 (a) Many chemical compounds used for rocket fuel and propellants are highly reactive and hazardous. One of these compounds, diborane, B 2H6, can be formed from its elements according to the following equation: 2B(s) + 3H2(g) → B2H6(g) Given the following data, 2B(s) + 3 2O2(g) → B2O3(s) ΔH1 ⦵ = −1273 kJ mol−1 B2H6(g) + 3O2(g) → B2O3(s) + 3H2O(l) ΔH2 ⦵ = −2035 kJ mol−1 H2(g) + 1 2O2(g) → H2O(l) ΔH3 ⦵ = −242 kJ mol−1 (i) Name the enthalpy change represented by ΔH1 ⦵. ……..…………………………………………………………………………………….. [1] (ii) Construct a suitable energy cycle and calculate the enthalpy change of formation of diborane, B2H6(g). [3] (b) The reaction of 2,2-dimethylhydrazine, (CH3)2N2H2, with dinitrogen tetroxide, N2O4, is another energy source for rockets. (CH3)2N2H2(l) + 2N2O4(l) → 2CO2(g) + 3N2(g) + 4H2O(g) ΔS⦵ = +1141.2 J K‒1 mol‒1 (i) One of the reactants in the above reaction , dinitrogen tetroxide, N2O4, may be obtained from the more commonly available NO2. State and explain the effect on the entropy, S, of the chemical system during the conversion of NO2(g) to N2O4(g). …………………………………………………………………………………… ..….…..... …………………………………………………………………………………… ..….…..... ……………………… …………………………………………………………… ..….….... …………………………………………………………………………… ………………[1]

3 9729/02 CJC JC2 Preliminary Examination 2025 [Turn over (ii) By using the standard enthalpy change of formation, ΔHf ⦵, values given below, calculate