CJC 2024 Prelim H1 Chem Paper 2 Solutions

CANDIDATE NAME CLASS 2T CHEMISTRY 8873/02 Paper 2 Structured Questions 26 August 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. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all the questions. Section B Answer one question. The use of an approved scientific calculator is expected where appropriate. You are reminded of the need for good English and clear presentation in your answers. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part of the question. This document consists of 28 printed pages Section A Q1 10 Q2 9 Q3 10 Q4 21 Q5 10 Section B Q6 20 Q7 20 Paper 2 (67%) 80 Paper 1 (33%) 30 Percentage Grade Catholic Junior College JC2 Preliminary Examinations Higher 1

2 8873/02/CJC JC2 Preliminary Examinations 2024 1 Dioxygen, O2 and ozone, O3 are two allotropes of oxygen found in the atmosphere. The thermochemical equation for the reversible conversion between ozone and dioxygen is shown below. 2O3(g) ⇌ 3O2(g) H = ‒286.0 kJ mol−1 (a) Draw the structure and suggest the shape of ozone, O3. Structure of O3 Shape of ozone: Bent [2] (b) Using Le Chatelier’s Principle, explain why an increase in temperature causes the ozone concentration to increase. ................................ ................................ ................................ ................................ ....... ................................ ................................ ................................ ................................ ....... ................................ ................................ ................................ ................................ ....... ................................ ................................ ................................ ................................ ... [2] (c) Sketch, on the same axis below, two graphs that show how the rate of forward and reverse reactions vary over time. Label your graphs clearly and indicate t, the time when equilibrium was established. [1] time rate By Le Chatelier’s Principle, an increase in temperature favours the endothermic reaction which is the backward reaction. in this instance. Hence, position of equilibrium shifts to the left resulting in an increase in the concentration of ozone. t Rate of forward reaction, Rf Rate of reverse reaction, Rb

3 8873/02 CJC JC2 Preliminary Examinations 2024 [Turn over (d) The diagram below shows that the concentration of ozone in the atmosphere varies with altitude above sea level. Diagram taken fr