2021_YIJC_Prelim_P2_Ans

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME CG INDEX NO H1 GROUP CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 8873/02 30 August 2021 2 hours READ THESE INSTRUCTIONS FIRST This document consists of 24 printed pages and 0 blank page. For Examiner’s Use Paper 1 /30 Paper 2 1 /14 2 /6 3 /10 4 /14 5 /16 6 or 7 /20 Penalty /80 Overall (Paper 1 & 2) Percentage (%) /110 Write your name, index number and CG 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 stap les, paper clips, highlighters, and glue or correction fluid/tape. 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. 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.

2 ©YIJC [Turn over Section A Answer all the questions in this section, in the spaces provided. 1 At 573K phosphorus( V) chloride, PC l5(g), decomposes to form phosphorus( III) chloride, PCl3(g), and chlorine, Cl2(g). A dynamic equilibrium is established as shown. PCl5(g) ⇌ PCl3(g) + Cl2 (g) numerical value of Kc = 0.625 (a) (i) Explain what is meant by the term dynamic equilibrium. [1] A dynamic equilibrium refers to a reversible reaction where the forward and reverse reactions are continuing at the same rate. (ii) Suggest and explain two changes which will increase the decomposition of PCl5. [2] Addition of PC l5 / removal of C l2 or PC l3 which will cause the position of equilibrium to shift to the right to remove the added PCl5 A smaller pressure / larger volume which will cause the equilibrium position to shift to the right to favour the formation of more gaseous particles. (iii) The experiment was repeated at 473K. The numerical value of Kc was found to be 8.3 x 10 –3. Deduce whether the decomposition reaction is exothermic or endothermic. Explain your answer. [2] - A lower temperature favours exothermic reaction (so as to release heat and decrease temperature) - At lower temperature, the value of Kc decreases, indicating that the backward reaction is favoured . Link: Since the backward reaction is e xothermic, the decomposition reaction (forward reaction) is endothermic .