ACJC 2015_H1_CHEM_P2_Answers Prelims

2 © ACJC 2015 8872/02/Prelim/15 [Turn over Section A Answer all questions in this section in the spaces provided. 1 Oxides of nitrogen are by -products of combustion of hydrocarbon fuels in internal combustion engines. One of them is nitrogen monoxide. At 700 °C, nitrogen monoxide and hydrogen react as follows: 2NO(g) + 2H2(g)  N2(g) + 2H2O (g) Keeping the concentration of nitrogen monox ide to be constant at 0.012 mol dm-3, the following graph was obtained. For Examiner’s use (a) (i) Calculate its initial rate of this reaction. [1] Initial rate = 6.67 x 10-6 mol dm-3 s-1 (ii) The results of some investigation of the rate of reaction are shown below. Experiment Number Initial [NO]/ mol dm-3 Initial [H2]/ mol dm-3 Initial Rate/ x 10-6 mol dm-3 s-1 1 0.0120 0.002 13.0 Using the given information and your answer in (i), determine the order of reaction with respect to hydrogen. [1] Comparing experiment 1 and keeping initial [NO] constant, the initial rate doubles when the initial [H 2] doubles, hence order of reaction wrt H2 is 1. (iii) Using the information below, d educe the order of reaction with respect to NO. Show your working clearly. Experiment Number Initial [NO]/ mol dm-3 Initial [H2]/ mol dm-3 Initial Rate/ x 10-6 mol dm-3 s-1 2 0.0020 0.012 2.2 3 0.0040 0.012 8.7 [2] [H2]/ mol dm-3 Time/ s

3 x x .0040)k(0.012)(0 .0020)k(0.012)(0 3 Rate 2 Rate  x      2 1 6- -6 8.7x10 2.2x10 x = 2 (iv) Determine a value of k, stating the units. [2] Using experiment 1, 13 x 10-6 = k(0.012)2(0.0020) k = 45.1 mol-2 dm6 s-1 (b) Write equations inclu ding state symbols for the reaction of the following oxides with water. In each case, state the pH of the resulting solution. (i) Na2O [1] Na2O(s) + H2O(l)  2NaOH(aq) pH=13 (ii) P4O6 [1] P4O6(s) + 6H2O(l)  4H3PO3(aq) pH 2 or 3 [Total: 8 marks] 2 During the OPEC 1973 oil crisis, methanol from coal is proposed as a proven liquid fuel with well -established manufacturing technology and sufficient resources to replace gasoline. T he enthalpy of combustion of methanol in a typical car engine is -715 kJ mol–1. In a methanol plant, its production is carried in 2 steps. The first step is to convert the feedstock natural gas into a synthesis gas stream consisting of carbon monoxide, carbon dioxide, steam and hydrogen. Methanol can then be produced by using the following reversible reaction between carbon monoxide and hydrogen. 2H2(g) + CO(g) CH3OH(g) For Examiner’s use (a) (i) It is recommended that the temperature of a stationery or slow