Hello, This is my first post on here, so thank you in advance for your help. 1. The problem statement, all variables and given/known data I have an air tight vessel that has a volume of 1m^3. The bottom of the vessel has water in it. What internal pressure is needed inside the vessel to achieve a temperature of 45C and 75% Relative Humidity? Also, what is the partial pressure of water vapor at that condition? 2. Relevant equations None Given. 3. The attempt at a solution I can't figure out how to figure out the mass/moles of water vapor in the air in order to figure out partial pressure and, thus, the relative humidity. I can't figure out how to get the overall pressure without knowing the mass/moles of water vapor in the air either. So I just need to know how to get started and i think I can finish it. again, thanks for your help.