CIE Nov 2017 v2 Paper 2 Q2

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At 450 K phosphorus(V) chloride, PCl 5(g), decomposes to form phosphorus(III) chloride, PCl 3(g), and chlorine, Cl 2(g). A dynamic equilibrium is established as shown. PMT PCl 5(g) PCl 3(g) + Cl 2(g) H = +124 kJ mol1 (a) The enthalpy change of formation of PCl 3(g) under these conditions is given. Hf PCl 3(g) = 320 kJ mol1 Calculate the enthalpy change of formation of PCl 5(g) under these conditions. Include a sign with your answer. enthalpy change =kJ mol1 [1] (b) (i) State and explain the effect of increasing temperature on the rate of decomposition of PCl 5(g).[2] (ii) State and explain the effect of increasing temperature on the percentage of PCl 5(g) that decomposes.[2] (c) Explain the meaning of the term dynamic equilibrium and the conditions necessary for it to become established.[2]UCLES 2017 9701/22/O/N/17<br /> (d) When 2.00 mol of PCl 5(g) are decomposed at 450 K and 1.00105 Pa the resulting equilibrium mixture contains 0.800 mol of Cl 2(g). (i) Calculate the partial pressure of phosphorus(V) chloride, pPCl 5, in this equilibrium mixture. PMT (ii) Write the expression for the equilibrium constant, Kp, for the decomposition of PCl 5(g). pPCl 5 =Pa [2] Kp = (iii) The partial pressures of PCl 3(g) and of Cl 2(g) in this equilibrium mixture are both 2.86104 Pa. Calculate the value of Kp and state its units. [1] Kp =units =[2] [Total: 12]UCLES 2017 9701/22/O/N/17 [Turn over<br />

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