5-kg of air at 427°C and 600 kPa are contained in a piston-cylinder device. The air expands adiabatically until the pressure is 100 kPa and produces 600 kJ of work output. Assume air has constant specific heats evaluated at 300 K.
(a) Determine the entropy change of the air, in kJ/kg·K
(b) Since the process is adiabatic, is the process realistic? Using concepts of the second law, support your answer.