NJC Physical Chemistry Revision Part 2 with answers

Physical Chemistry Revision Part 2 No. Topic Questions Page Answers Page 1 Chemical Equilibrium 1-17 17-44 2 Acid Base Equilibrium 45-62 63-79 3 Solubility Equilibrium 80-91 91-101 4A Electrochemistry (Electrochemical Cells) 102-116 126-137 4B Electrochemistry (Electrolytic Cells) 117-121 137-142 4C Electrochemical and Electrolytic Cells 121-126 142-146 Copyright © National Junior College All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any other information storage and retrieval system, without prior permission in writing from the copyright owner.

National Junior College SH2 H2 Chemistry 1 1) Chemical Equilibrium MCQ 1 Nitrogen dioxide decomposes on heating according to the following equation. 2NO2(g) 2NO(g) + O2(g) When 4 mol of nitrogen dioxide were put in a 1 dm 3 container and heated, the equilibrium mixture contained 0.8 mol of oxygen. What is the equilibrium constant, Kc, at the temperature of the experiment? A 0.8 × 0.82 2.42 B 0.8 × 1.62 2.42 C 0.8 × 0.82 42 D 0.8 × 1.62 42 2 If compound A is heated, it decomposes according to the equation: 2A(g) B(g) + C(g) The following diagram shows the progress of the reaction. Determine the value of equilibrium constant Kc. A 0.8 B 2.0 C 4.0 D 10.0 Concentration / mol dm-3 Time / hours

National Junior College SH2 H2 Chemistry 2 3 The key stage in the manufacture of sulfuric acid is the reaction between sulfur dioxide and oxygen to form sulfur trioxide. 2SO2(g) + O2(g) ⇌ 2SO3(g) When 0.50 mol of SO2 and 1.00 mol of O2 were reacted together in a container of volume 0.5 dm3, 0.30 mol of SO3 was present in the equilibrium mixture. What is the numerical value of the equilibrium constant, Kc, for the equilibrium reaction below? SO2(g) + 1 2O2(g) ⇌ SO3(g) A 0.66 B 1.15 C 1.32 D 1.63 4 Consider the following equilibrium: When Q2 is allowed to react with R 2 in a molar ratio of 2:1 at a total initial pressure of 3 atm, 20% of the equilibrium mixture is found to be Q2R. What is the equilibrium constant, Kp, of this reaction? A 0.0174 atm−1 B 0.0781 atm−1 C 0.194 atm−1 D 0.232 atm−1 5 The contact process is an important industrial reaction which produces sulfuric acid. One of the steps of the process involves the addition of excess oxygen to sulfur dioxide to produce sulfur trioxide gas in an equilibrium reaction: 2SO2(g) + O2(g) 2SO3(g) SO2(g) and O 2(g) were mixed in a 1:2 ratio and the mixture was kept at a constant pressure of 5 atm. At equilibrium, it was found that 30% of the sulfur dioxide was consumed. What is the numerical value of Kp of this reaction? A 0.0566 B 0.142 C 1.75 D 8.35

National Junior College SH2 H2 Chemistry 3 6 A 1:3 molar mixture of X2 and Y2 is heated at 673 K and 100 atm of constant pressure so that it comes to equilibrium. The equilibrium mixture contains 20 % of XY3. X2 (g) + 3Y2 (g) 2XY3 (g) Using the equation above, what is the numerical value of Kp for the reaction at 673 K? A 9.26 x 10-5 B 2.93 x 10-4 C 2.50 x 10-4 D 5.68 x 10-4 7 Ammonia decomposes into hydrogen and nitrogen gas at high temperatures. 2NH3(g) N2(g) + 3H2 (g) Ammonia at pressure P was placed in an evacuated reactor which was maintained at constant temperature. At equilibrium, the ratio of nitrogen to ammonia was found to be 1:3. What is the equilibrium constant, Kp, for the reaction? A 3P2 B 75P2 C D 8 The following reaction is used industrially to produce a combustible gas from coal. H2O(g) + C(s) H2(g) + CO(g) A mixture of powdered coal and steam at a pressure of 1 atm was allowed to reach equilibrium at a constant temperature of 500 K. At equilibrium, the total pressure had increased to 1.9 atm. What is the numerical value of the equilibrium constant, Kp, at 500 K? A 1.9 B 3.24 C 8.1 D 81 9 A pure sample of NH3(g) is introduced into an evacuated vessel of constant volume. This vessel is maintained at constant temperature such that the equilibrium below is established. 2NH3(g) N2(g) + 3H2(g) The value of the final pressure is then found to be 40 % greater than if only NH 3 were present. What is the mole fraction of H2 in the reaction mixture? A 0.14 B 0.29 C 0.43 D 0.72

National Junior College SH2 H2 Chemistry 4 10 Given the following reaction: A (g) + B (g 2C (g) + 2D (g) Kp = 2.10 x 102 atm2 An equimolar mixture of A and B is allowed to reach equilibrium at 700 K. Determine the total pressure at equilibrium if the partial pressure of C at equilibrium is found to be 2.00 atm. A 1.28 atm B 4 atm C 4.28 atm D 4.56 atm 11 Given that the Kp for the following equilibrium is 125 at 65oC, X(s) + 3Y(g) ⇌ 3Z(g) What is the mole ratio of Y : Z at equilibrium at 65oC? A 1 : 1 B 1 : 5 C 25 : 1 D 125 : 1 12 An equilibrium can be represented by the following equation: In a certain mixture, the equilibrium concentration of Q is 10 mol dm−3. What will be the new equilibrium concentration of Q if 5 mol of pure Q is dissolved in the mixture? A 15 mol dm−3 B between 10 mol dm−3 and 15 mol dm−3 C 10 mol dm−3 D between 5 mol dm−3 and 10 mol dm−3 13 Ammonia is manufactured industrially by the Haber Process as shown. N2(g) + 3H2(g) 2NH3(g) ∆H < 0 The operating conditions are: 400 to 450 °C; a pressure of 200 atm; an iron catalyst Which of the following statement(s) is/are true about the Haber process for the manufacture of ammonia? 1 At higher temperatures, the production of ammonia becomes thermodynamically less feasible. 2 At higher pressures, the yield goes down but the rate of production of ammonia is faster. 3 The presence of a catalyst shifts the equilibrium position to the right and increases the yield.

National Junior College SH2 H2 Chemistry 5 A 1,2 and 3 are correct B 1 and 2 only are correct C 2 and 3 only are correct D 1 only is correct 14 The diagram below represents the reaction profile of the monomer-dimer system: Which statement about the equilibrium is correct? A The equilibrium constant Kc will be larger at higher temperatures. B kf increases and kb decreases when the equilibrium mixture is heated. C Doubling the total pressure of the system reduces the percentage dissociation to half. D At higher temperature, the colour intensity of the mixture increases. 15 Ammonia is manufactured in the Haber process. N2 (g) + 3H2 (g) 2NH3 (g) ΔH = –92 kJ mol–1 Given that Kp for the above reaction is 3.375 at T K, which of the following statements involving the reaction is correct? 1 The partial pressure of H 2 (g) at equilibrium at T K can be expressed as 2 When equilibrium is established, temperature, T K, is given by 3 When pressure is increased, the yield of ammonia and the equilibrium constant increases A 1,2 and 3 are correct B 1 and 2 only are correct C 2 and 3 only are correct D 1 only is correct Enthalpy Progress of reaction

National Junior College SH2 H2 Chemistry 6 16 The values of the equilibrium constant, Kp, for the reaction Ag2CO3(s) Ag2O(s) + CO2(g) are 0.313 kPa and 115 kPa at 25 °C and 727 °C respectively. What deduction can be made from the information given above? A The yield of CO 2 can be increased by adding some Ag 2CO3 to a system already in equilibrium. B The activation energy of the reverse reaction is higher than that of the forward reaction. C Less CO2 is formed at equilibrium if the reaction is allowed to take place in another container of a smaller volume. D More CO2 is formed at equilibrium if a suitable catalyst is used. 17 A system at equilibrium is