$3-44$ Water initially at $200$ kPa and $300C$ is contained in a piston$-$cylinder device fitted with stops. The water is allowed to cool at constant pressure until it exists as a saturated vapor and the piston rests on the stops. Then the water continues to cool until the pressure is $100$ kPa $.$ On the $T-$ diagram, sketch, with respect to the saturation lines, the process curves passing through the initial, intermediate, and final states of the water. Label the $T,P,$ and $$ values for end states on the process curves. Find the overall change in internal energy between the initial and final states per unit mass of water.