(a) The critical point of krypton, Kr, is found at Tc = 63.7 C and pc = 5.53 106 Pa. The triple point of Kr is found at T3 = 157 C and p3 = 74.1 103 Pa. The van der Waals parameters for Kr are a = 0.235 N m4 mol2 and b = 39.8 106 m3 mol1.

(iii) By considering the compressibility, Z (Equation Q3.b), comment on how suitable the van der Waals equation is for Kr in this sample. (4 marks)

(b) Explain, in terms of Gibbs free energy, the phase changes that occur to Kr as a result of increasing temperature. Sketch an appropriate graph as part of your answer. (7 marks)

(c) Calculate the change in chemical potential for both the gas phase and liquid phase of Kr as a result of a pressure decrease of 3 bar. Is the Kr more or less likely to be in the liquid phase after this change? (6 marks)