TJC_08 TJC Chem H2 Prelim P3

TEMASEK JUNIOR COLLEGE CHEMISTRY 9746/03 Higher 2 Paper 3 Free Response Thursday 11th SEPTEMBER 2008 2 hours Candidates answer on separate paper. Additional materials: Answer paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, centre/index number & CG in the spaces provided on the cover page provided and 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 staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. You may use a calculator. A Data Booklet is provided. At the end of the examination, fasten all your work securely together You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. This question paper consists of 12 printed pages. [Turn over

2 [Turn over [Turn over Answer any four questions. 1. ) ome data on three nitrogen-containing compounds are given in the table below: Compound Molecular formula Boiling point/ C (a S o Dinitrogen pentoxide N 2O5 decomposes nitric acid HNO3 83 nitrosyl chloride NOCl -6.4 (i) symmetrical molecule) and NOCl. Indicate the relevant bond angles in each case. (ii) ference in the boiling points of HNO3 and NOCl in terms of structure and bonding. [6] (b) oxide and chlorine is an endothermic process hich takes ing to the equation: 2NOCl (g) 2NO (g) + Cl2 (g) ∆H > 0 3 vessel at 400 K, 0.5 mol of NOCl is injected and the equilibrium pressure is 101 kPa. (i) e the total number of moles of gas at equilibrium, assuming the gases behave ideally. (ii) ence calculate the percentage of the nitrosyl chloride that has dissociated. Draw diagrams to illustrate the shapes of N2O5 (a Explain the dif The dissociation of nitrosyl chloride into nitric w place accord In an evacuated 20 dm Calculat H

3 [Turn over [Turn over A mixture of NOCl, NO and Cl2 is injected into a second evacuated vessel of a fixed volume at 400 K. It takes 10 minutes for the system to reach equilibrium and the equilibrium pressure is 200 kPa. The initial and final compositions of the mixture of gases are shown in the table below. Initial number of moles at 400 K Equilibrium number of moles at 400 K NOCl 0.5 0.3 NO 0.1 0.3 Cl2 0.1 0.2 (iii) Write an expression for Kp for the reaction and calculate Kp, stating its units at 400 K. (iv) The temperature of the system in the second vessel is increased to 500 K at time, t = 25 minutes. Suggest, with an explanation, how the position of equilibrium might change. Give a sketch to show how the number of moles of nitrosyl chloride gas might change with time from t = 0 min to t = 40 min. [9] (c