The ideal gas in the cylinder in Fig. 21-1 is initially at conditions P1, V1, T1. It is slowly expanded at constant temperature by allowing the piston to rise. Its final conditions are P2, V2, T1, where V2 = 3 V1. Find the change in entropy of the gas during this expansion. The mass of gas is 1.5 g, and M = 28 kg/kmol for it.