1. Calculate the internal energy change per unit mass for the substances and states given below.
a. Water: $T_1 = 0^\circ C$, $P_1 = 2 \text{ MPa}$, $T_2 = 400^\circ C$, $P_2 = 2 \text{ MPa}$
b. $CO_2$: $P_1 = 15 \text{ psia}$, $T_1 = 40^\circ F$, $P_2 = 30 \text{ psia}$, $T_2 = 1040^\circ F$
c. $H_2$: $P_1 = 100 \text{ kPa}$, $T_1 = 0^\circ C$, $P_2 = 200 \text{ kPa}$, $T_2 = 1000^\circ C$