Determine the change in specific entropy between states 1 and 2 of the fluids given below:
(a) R-134a. State 1: T1=0C, p1= 4.1 bar , State 2: T2 = 20C, p2= 4.0 bar
(b) Water. State 1: T1 = 90C, x1 = 0.8 , State 2: T2= 600C, p2 = 68.0 bar
(c) Ammonia. State 1: T1 = -4F, p1 = 10 lbf/in^2 , State 2: T2 = 17F, p1 = 30 lbf/in^2 provide work