I'm studying vapor pressure and I'm having trouble to understand some concepts. Vapor pressure depends only on the temperature of the liquid in question right? For example, if we have a container with water at 30° C, it doesn't matter the experiment, would it ALWAYS be a vapor phase with pressure = vapor pressure of water at 30°C = 31.8 mmHg? So consider the following experiment: In a container we have water at 30°C. One end is closed while in the other we have a piston. Above the pistons we have weights that do a initial pressure of 200mm Hg on the water. Is there water in the vapor state? I would say yes, but if so the vapor should exert a pressure of 31.8mmHg, and where would be the other 268.2mm Hg? The only explanation I thought is that a few bubbles of gas above the liquid makes the 31.8mmHg but the liquid still stays in contact with the piston making the other 268.2 mmHg. But I haven't read this in anywhere, is it right?