2021_TJC_H2Chemistry_P3_Ans Prelim

1 DO NOT WRITE IN THIS MARGIN [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC PRELIM / 2021 CANDIDATE NAME CIVICS GROUP / CENTER NUMBER S INDEX NUMBER CHEMISTRY 9729/03 Paper 3 Free Response 13 September 2021 2 hours Candidates answer on the Question Paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Civics Group, Centre number, index number and name in all the work you hand in. Write in dark blue or black pen. You may use a 2B 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 pages 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. 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 Paper 3 (Section A) 1 2 3 Paper 3 (Section B) 4 5 Total This document consists of 23 printed pages and 1 blank page. PRELIMINARY EXAMINATIONS HIGHER 2

2 DO NOT WRITE IN THIS MARGIN [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC PRELIM / 2021 SECTION A Answer all the questions in this section. 1 (a) The Contact Process is an industrial process for manufacturing sulfuric acid. The key stage in this process is the reaction between sulfur dioxide and oxygen. 2SO2(g) + O2(g) ⇌ 2SO3(g) DH = –197 kJ mol–1 Vanadium(V) oxide, V2O5, is used as a heterogeneous catalyst for this process. With the aid of an energy profile diagram, explain using collision theory why the addition of the catalyst speeds up the reaction. [3] • Well-labelled diagram The √ catalyst provides an alternative pathway, one which involves a lower Ea than that of an uncatalysed reaction. √ Number of molecules having energy greater than or equal to Ea’ increases significantly. The √ frequency of effective collisions increases, √ rate constant, k increases and thus rate increase. 2√: 1m (b) In an experiment to determine the Kp of the Contact Process in (a), a mixture containing 0.200 mol of SO2 and 0.100 mol of O2 was heated in a closed flask and allowed to reach equilibrium at 550 oC and 3.5 atm. The f