[ana2345]

If I'm given a table with the vapor pressure of a substance at various temperatures, how should I calculate its enthalpy of vaporization? I found an equation in the back of my textbook that says:

$$ \ln{(P_\text{vap})} = -\frac{\Delta H_\text{vap}}{R} \left(\frac{1}{T}\right) + C /$$,

So I gather I should take all of the vapor pressure data and take the logarithm of each, and take the reciprocals of the temperature data.... and then do a linear fit to find the slope and intercept of the line they make?

Can someone please help me understand how this equation was derived, and why vapor pressure and enthalpy of vaporization are related in this way? And what does the constant C represent?