1. The problem statement, all variables and given/known data Sealed container which is used to heat 200 kg water is initially at 25 degrees C. Since the container is sealed, the water remains in saturated state while its temperature and pressure increases. The remaining volume of the container is filled with water vapor at the same temperature and pressure. There is a pressure safety valve on the container. a) If the max allowed water temperature is 150 degrees C, at what pressure should the safety value open? b) How much energy is needed to increase temperature of water from 25 degrees C to 150 degrees C? You can neglect mass of water vapor and assume closed system containing only 200 kg of water. 2. Relevant equations PV = mRT where m = R/M (M = molar mass). 3. The attempt at a solution I cannot find a definitive source which will confirm that I can use the ideal gas law on this problem. In addition, water vapor and water have different specific heats at a constant pressure and I must account for the total pressure within the system. Do I need to split the system into two separate parts and calculate the pressure in each individual part as the temperature is raised? This doesn't seem logical to me -- the pressure valve needs to be set based on what the total pressure of the system will be.... Any advice? Just not sure how to attack this guy.