7: A piston cylinder device initially contains 3.6L of air at 137 kPa and 28 C. Air is now compressed to a final state of 830 kPa and 231 C. The useful work input is 1.9 kJ. Assume the surroundings are at 112 kPa and 15 C. The gas constant of air is R = 0.287 kPa.m3 /kg.K. The specific heats of air at the average temperature of 360 K are cp = 1.009 kJ/kg·K and cv = 0.722 kJ/kg·K. a. Determine the entropy change per unit mass, (s2 - s0). b. Determine the volume change per unit mass, (v2 – v0). c. Determine the exergy of the air at the initial and the final states. d. Determine the minimum work that must be supplied to accomplish this compression process. e. Determine the second law efficiency of this process.