(a) Show, for a perfect gas undergoing a process between states 1 and 2, that the change in specific entropy is given by S2 - S1 = R In " ) + co (b) A perfect gas undergoes an expansion from a pressure, p1 to a pressure, p2 such that pun=constant. Determine an expression for the change in specific entropy of the gas in terms of the initial and final pressures and the gas constants