DHS H2 Chem 2013 Prelim P3 QP

This question paper consists of 10 printed pages and 0 blank page. © DHS 2013 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY 9647/03 Paper 3 24 September 2013 Paper 2 2 hours Additional Materials: Data Booklet, Graph Paper & Writing Paper IMPORTANT INSTRUCTIONS TO CANDIDATES 1 Answer any four questions. 2 Begin each question on a fresh sheet of paper. 3 At the end of the examination: • Staple or fasten all your work securely together with the Cover Sheet on top. • Hand in the question paper separately. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You are advised to show all workings and calculations. You are reminded of the need for good English and clear presentation in your answers. 524

2 © DHS 2013 9647/03 [Turn Over Answer any four questions. Begin each question on a fresh sheet of paper. 1 Dinitrogen pentoxide, N2O5, can be produced by the following reaction sequence in the car engine: I N2(g) + O2(g) → 2NO(g) ∆Hθ = +180 kJ mol–1; ∆Sθ = +24.8 J mol–1 K–1 II NO(g) + 1/2O2(g) → NO2(g) ∆Hθ= –57.0 kJ mol–1 III 2NO2(g) + 1/2O2(g) → N2O5(g) ∆Hθ = –110 kJ mol–1 (a) (i) Explain why reaction I does not take place at room temperature but occurs in car engine. (ii) Predict, with reasons, the sign of ∆Sθ in reaction II. (iii) Nitrogen dioxide is a pollutant that is often produced in car engine. Suggest how the pollutant can be removed in the car engine. (iv) By drawing a suitable energy cycle and using the data above, calculate the standard enthalpy change of formation of dinitrogen pentoxide. [8] (b) The rate of reaction for reaction II was investigated and the following kinetics data was obtained. Time/minutes Experiment 1, with [NO] = 0.10 mol dm –3 Experiment 2, with [NO] = 0.05 mol dm–3 [O2] / mol dm–3 [O 2] / mol dm–3 0 0.0050 0.0050 5 0.0031 0.0045 10 0.0019 0.0040 15 0.0011 0.0036 20 0.0007 0.0032 25 0.0005 0.0029 30 0.0004 0.0026 (i) Explain why nitrogen monoxide is used in large excess. (ii) Using the same axes, plot graphs of [O2] against time for the two experiments. (iii) Use your graphs to determine the order of reaction with respect to O 2 and NO, showing your workings clearly. (iv) State the rate equation of reaction II and hence calculate the rate constant, including its units. (v) Explain how the half–life of oxygen will be affected when the concentration of nitrogen monoxide is doubled. [10] (c) The nitrogen dioxide produced in reaction II is able to form dinitrogen tetraoxide as shown below: 2NO2(g) N2O4 (g) brown colourless 525

3 © DHS 2013 9647/03 [Turn Over Explain whether the enthalpy change of dimerisation is endothermic or exothermic. Hence, pred