Question

Find the change in entropy when (a) 3.0 kg of boiling water changes to steam at 100°C. (b) 3.0 kg of water is heated from 20°C to 80°C, and (c) 2.0 kg of water at 30° are mixed with 5.0 kg of water at 75°C and the mixture allowed to reach equilibrium.

Answer 1

(a) $S=2257/373.15=6.05\text{ kJ/(kg K)}.$

(b) $S=mC\ln(T_2/T_1)=2.35\text{ kJ/(kg k)}.$

(c) $S=(m_1+m_2)c\ln(T_{f.mixture}/T_{av.initial})=855\text{ kJ/(kg K)}.$