ALS6Q - Section 6 Chemical Equilibria 1 SKH Bishop Baker...

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Section 6/ Chemical Equilibria / SKH Bishop Baker Secondary School AL Chemistry Section 6 Chemical Equilibria 81 IB Q.5 (b) A mixture of 4.0 mol of H 2 (g) and 2.0 mol of I 2 (g) was made to react at temperature T and pressure P . When equilibrium was reached, it was found that 3.6 mol of HI(g) were present. (i) Give the expression for the equilibrium constant K p and K c for the reaction H 2 (g) + I 2 (g) === 2HI(g) (ii) Calculate the equilibrium constant K c . (4 marks) 82 IB Q.9 (a) Solid ammonium hydrogen sulphide dissociates into hydrogen sulphide and ammonia as represented by the following equation : NH 4 S(s) === H 2 S(g) + NH 3 (g) At 295 K, when solid ammonium hydrogen sulphide is introduced into an evacuated vessel, the total pressure at equilibrium of the gas mixture is found to be 0.54 atm. (i) Calculate the equilibrium constant, K p , for the reaction. (ii) If the vessel initially contains hydrogen sulphide gas at a pressure of 0.335 atm, what is the partial pressure of ammonia when the system is allowed to reach equilibrium at the same temperature ? (6 marks) 83 IA Q.1 (d) Consider the following equilibrium reaction : BiCl 3 (aq) + H 2 O(l) === BiOCl(s) + 2HCl(aq) Starting from a sample of BiOCl, describe an appropriate method to demonstrate the above equilibrium. (2 marks) 83 IB Q.9 (b) Consider the reaction H 2 (g) + ½O 2 (g) === H 2 O(g) (i) Write down the expression for K p . (ii) At 298 K, the numerical value of K p is 1.18 x 10 40 . Show that at equilibrium the reaction goes almost to completion to the product side. (No calculation is required.) (2 marks) 84 IB Q.8 (a) The graphs below give the percentage of Z in the equilibrium mixture at constant pressure and constant temperature for the reversible reaction : x X(g) + y Y(g) === z Z(g) 1
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Section 6/ Chemical Equilibria / Suggest how you would increase the yield of Z. (i) In practice, the conditions chosen for the synthesis of Z are 723 K and 250 atm. Justify this choice. (ii) A catalyst has been used for the above reaction to give the results shown. What would happen if the catalyst were poisoned? Draw a new graph for the reaction at 837 K to illustrate your answer. (iii) Suppose the equilibrium constant for the above reaction is K, the rate constant for the forward reaction is k 1 , and the rate constant for the backward reaction is k - 1 . Express K in terms of k 1 and k - 1 . (11 marks) 85 IA Q.1 (c) For the following system at equilibrium SnO 2 (s) + 2CO(g) === Sn(s) + 2CO 2 (g), write an expression for the equilibrium constant. What data would be required to determine the value of your equilibrium constant at a given temperature ? (3 marks) 86 IIA Q.3 (a) The following table gives the equilibrium constant, K p , at several temperatures for the dissociation of ethanoic acid dimers in the gas phase : T / K 298 303 308 313 K p / N m -2 72.9 121.1 182.7 302.0 (i) Calculate the degree of dissociation at 298 K and a total pressure of 1500 N m -2 . (ii) Show graphically that the data obey the equation
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ALS6Q - Section 6 Chemical Equilibria 1 SKH Bishop Baker...

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