I have to calculate the vapor pressure of water at 25.0 degrees celicus. The heat of vaporization of water is 40.65 kj/mol and the vapor pressure of water is 92.7 Torr at 50 degrees celcius. I know I should use log10 P=A- B/C+T but I don't know how to work it out.

Answer 1

I am not familiar with your equation. I would use the Clausius-Clapeyron equation (and please note the correct spelling of celsius).
ln(p2/p1) = dHvap/R(1/T1-1/T2)
If you let p1 = 92.7 and T1 = 50C+273; then solve for p2 = ? when T2 = 25+273