CJC_Prelim H1 Chem 2008 P2

Name Class: 2T CATHOLIC JUNIOR COLLEGE PRELIMINARY EXAMINATION 2008 CHEMISTRY 8872/02 Higher 1 Paper 2 26 August 2008 2 hours Candidates answer Section A on the Question Paper and Section B on separate paper. Additional Materials: Paper 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 on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer any two questions. 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 Section A B5 B6 B7 Total There are a total of 12 printed pages including this cover page. 8872/02/CJC Prelim 08 1

SECTION A Answer all the questions in this section in the spaces provided. 1 The equation for the decomposition of gaseous X at 373 K is shown below. 2X (g) Y (g) + Z (g) The values for the initial rates of decrease in concentration of X at various initial concentrations have been determined. These are shown in the table below. Initial concentration / mol dm -3 1.67 3.34 5.01 6.68 Initial rate / mol dm-3 s-1 0.41 1.64 3.69 6.56 (a) (i) Determine the order of reaction with respect to X and hence write the rate equation for this reaction. (ii) Calculate the rate constant for this reaction, stating the units clearly. [4] (b) (i) At 373 K, the activation energy for the forward reaction is 130 kJ mol -1 and that for the reverse reaction is 72 kJ mol-1. Sketch and label the energy profile diagram for this reaction. (ii) Hence, determine the value of the enthalpy change of the decomposition reaction. [3] 8872/02/CJC Prelim 08 2

(c) What will be the effects of increasing pressure on the decomposition of X? [2] (d) In the presence of a catalyst, the activation energy of the reverse reaction is 43 kJ mol -1. On the same axes in (b)(i), draw the energy profile of the catalysed reaction and label it clearly. [1] [Total: 10] 2 2-chloroethylbenzene can be formed stepwise from benzene via the following reaction scheme. CH2CH3