is more highly charged than Cl. is needed than Cl. (g) N 2 O 4 (g) 2NO 2, is negative. Hence the equilibrium constant, K p

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1 1 The value of E cell indicates whether the cell reaction is thermodynamically feasible. Which of the following is a correct statement about E cell? E cell is directly proportional to the equilibrium constant. E cell is directly proportional to the entropy change of the system, S system. E cell is directly proportional to the total entropy change, S total. The value of In E cell is directly proportional to the total entropy change, S total. 2 The enthalpy changes of the reactions below are similar. The equilibrium constants for the two reactions are K 1 and K 2 respectively. Reaction 1 Reaction 2 [u(h 2 O) 6 ] 2+ (aq) + ET 4 (aq) [u(et)] 2 (aq) + 6H 2 O(l) [u(h 2 O) 6 ] 2+ (aq) + 4l (aq) [ul 4 ] 2 (aq) + 6H 2 O(l) The value of K 1 is greater than K 2 because S system is much more positive in Reaction 1. S surroundings is much more positive in Reaction 1. the ET 4 is more highly charged than l. a lower concentration of ET 4 is needed than l. 3 For the reaction 2NO 2 (g) N 2 O 4 (g) at 450 K the total entropy change, S total, is negative. Hence the equilibrium constant, K p, for this reaction at 450 K is zero. positive and greater than 1. positive and less than 1. negative. PhysicsndMathsTutor.com

2 4 The overall equation for a reaction between two chemicals, M and N, is M + 2N P + Q (a) This reaction occurs spontaneously at room temperature. Which of the following must be true? H reaction H reaction S total S total is positive. is negative. is positive. is negative. (b) The reaction above occurs in two stages via an intermediate, T. M + N T N + T P + Q slow fast From this it can be deduced that the rate equation for the reaction between M and N is rate = k[m][n] rate = k[m][n] 2 rate = k[m][t] rate = k[n][t] = 2 marks) PhysicsndMathsTutor.com

3 5 alcium carbonate decomposes at high temperature to form calcium oxide and carbon dioxide: ao 3 (s) ao(s) + O 2 (g) alcium carbonate is thermodynamically stable at room temperature because for this reaction the activation energy is high. the enthalpy change, H, is positive. entropy change of the system (S system ) is positive. entropy change of the system (S system ) is negative. 6 2-methylpropane has a smaller standard molar entropy at 298 K than butane. The best explanation for this is that 2-methylpropane has a lower boiling temperature. a higher standard molar enthalpy change of formation. fewer ways of distributing energy quanta. more ways of distributing energy quanta. 7 PhysicsndMathsTutor.com

4 8 The reaction below is carried out at 25. Use the equation and the data to answer the questions that follow. SO 2 (g) + 2H 2 2 H Substance Standard molar entropy, S K SO 2 (g) 248 H 2 S(g) H 2 O(g) S(s) 32 K, is +233 K, is 2 marks) PhysicsndMathsTutor.com

5 9 decrease in the entropy of the system, S system, occurs when water freezes. water boils. water reacts with sodium. water reacts with ethanoyl chloride. 10 Which of the following is true for the exothermic reaction shown below? Mg(s) + 2Hl(aq) Mgl 2 (aq) + H 2 (g) H positive S surroundings S system S total positive negative negative 11 Which of these solid substances is likely to have the greatest standard entropy? Use of the data booklet is not required. SnO SnO 2 Snr 2 Snr 4 PhysicsndMathsTutor.com

6 12 Which reaction has the most positive entropy change for the system, S system? NaOH(aq) + Hl(aq) Nal(aq) + H 2 O(l) gno 3 (aq) + Nal(aq) gl(s) + NaNO 3 (aq) 2 H 4 (g) + Hl(g) 2 H 5 l(l) 4 H 10 (g) 2 H 4 (g) + 2 H 6 (g) 13 arium carbonate decomposes in an endothermic reaction when heated to 1500 K. ao 3 (s) ao(s) + O 2 (g) What are the signs of the entropy changes at 1500 K? S system S surroundings When ammonium nitrate crystals dissolve in water, the entropy of the system remains the same. falls, because the hydrated ions are more ordered than the solid. rises, because the ions in the crystal become hydrated in the solution. rises, because the ions are arranged more randomly in the solution than in the crystal. PhysicsndMathsTutor.com