Hi dear Forumers, I 've run into a little thermodynamic problem: There is a closed vessel, containing a given amount of liquid. I heat up the vessel, higher than the boiling point of the liquid. Here it is what happens: As a start, I know that the pressure inside the vessel consists of the vapor pressure of the liquid + the pressure of other gases (air). Increasing the temperature, the partial pressure of the air increases, simply according to ideal gases p ~ T. And the vapor pressure also increases. At a certain temperature, vapor pressure of the liquid will be equal to the pressure of the air inside the vessel, am I right? Then the liquid begins to boil. Question: How can we determine the portion of liquid and vapor? I tried to find it out by simply using ideal gas law. Volume of the vessel is given, so I can determine, how many liquid need to become vapor in order to reach the given vapor pressure at a given temperature. Then I can substract this amount from the volume of the liquid. And then I reach to the result, hopefully:shy:. Is this OK? I 'm afraid, because close to the boiling point it is not a wise thing to use ideal gas law. Please check my thoughts. . .