)2+=0—)学=(n)男 ds FIGURE 20-12 The integral, gas, of the entropy for a reversible cycle is zero. Hence the difference in entropy between states a and b b S ∫adS, is the same for path I as for path II.T dQ dS =   = b a T dQ b a T dQ ( ) + ( ) = 0 (I) (II)   a b T dQ b a T dQ I II