At 450 K phosphorus(V) chloride, PCl5(g), decomposes to form phosphorus(III) chloride, PCl3(g), and chlorine, Cl2(g). A dynamic equilibrium is established as shown. PCl5(g) ⇌ PCl3(g) + Cl2(g) ΔH = +124 kJ mol-1 When 2.00 mol of PCl5(g) are decomposed at 450K and 1.00 × 10^5 Pa the resulting equilibrium mixture contains 0.800 mol of Cl2(g).

1. (a)The enthalpy change of formation of PCl3(g) under these conditions is given. ΔH PCl3(g) = −320 kJ mol-1 Calculate the enthalpy change of formation of PCl5(g) under these conditions. Include a sign with your answer. enthalpy change = ...................................... kJ mol-1[1]
2. (b)(i)State and explain the effect of increasing temperature on the rate of decomposition of PCl5(g).[2]
3. (b)(ii)State and explain the effect of increasing temperature on the percentage of PCl5(g) that decomposes.[2]
4. (c)Explain the meaning of the term dynamic equilibrium and the conditions necessary for it to become established.[2]
5. (d)(i)Calculate the partial pressure of phosphorus(V) chloride, pPCl5, in this equilibrium mixture. pPCl5 = ........................................ Pa[2]
6. (d)(ii)Write the expression for the equilibrium constant, Kp, for the decomposition of PCl5(g). Kp =[1]
7. (d)(iii)The partial pressures of PCl3(g) and of Cl2(g) in this equilibrium mixture are both 2.86 x 10^4 Pa. Calculate the value of Kp and state its units. Kp = ........................................... units = ...........................................[2]