4. A rigid tank is divided into two equal parts by a partition. One part of the tank contains 3.0 kg of compressed liquid water at 400 kPa and 50°C, while the other part is evacuated. The partition is now removed and the water expands to fill the entire tank. Determine the entropy change of the water during this process, if the pressure in the tank is 30 kPa. [MO2]