It is important to know that under normal conditions, everything boils at 1atm. A liquid boils when its vapor pressure equals the exterior pressure, and since we're at 1atm, that is what the vapor pressure for a substance at its boiling point will be,
The most useful form of the Clausius-Clapeyron is
lnP2P1=−ΔHvapR1T2−1T1 ,where
P1- the vapor pressure of that substance at T1;
P2 - the vapor pressure of that substance at T2;
ΔHvap- the enthalpy of vaporization.
R- the gas constant - usually expressed as 8.314JK×mol