# Liquid-Vapor Equilibrium and Vapor Pressure

by jaumzaum
Tags: equilibrium, liquidvapor, pressure, vapor
 P: 248 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?
 P: 248 Correction: "Above the pistons we have weights that do a initial pressure of 300 mm Hg" Nobody knows the answer?
 PF Gold P: 860 I do not see the need to subtract the vapor pressure anywhere. There is the same pressure beneath the piston as beneath the closed end, so the full effect of the piston weight is transmitted.