Posted by Angel on .
If you can show me an example of one problem, I have no idea how to approach this.
Calculate where the number 40.67 came from.
Use the ClapeyronClausisus equation. Assuming that delta H vap does not change with temperature, this equation relates the change in vapor pressure and temperature to a substance's enthalpy of vaporization (R is the molar mass constant). Use this relationship and the fact that delta H vap of water at 25 degrees Celsius is 43.99 kJ/mol to calculate the vapor pressure of water at 5,25,50, and 95 degrees Celsius. Your results should be (in order and in Torr)

Chemistry 
DrBob222,
It's hard to explain a number that doesn't show up in the writing. But I think the 40.67 is the heat vaporization of water although the problem lists it as 43.99.