1. The problem statement, all variables and given/known data Trying to figure out the boiling point for a substance using this equation. I have 3 temperatures along with the pressure at those three temperatures. 2. Relevant equations lnP=−ΔHvap/RT+b 3. The attempt at a solution Ok, so obviously a plot of ln(P) vs. (1/T) gives you a slope of −ΔHvap/R. But what units should pressure be in for this equation? I don't get it, if you use R=8.314, all the units cancel out and ln(P) is unitless. I don't know whether to plot it with P in torr or atm. If I use P= 1 atm, ln(P) will equal zero and everything will cancel out. So can I not use atm here? EDIT: Ok I realize that it doesn't matter what units you plot it in, the slope is the same. But then actually using that value, what if I want to find what the temperature will be at 1 atm? EDIT 2: Do I have to use the equation in the other form of the Clausius Clapeyon equation, i.e. ln(p2/p1)=-H/R (1/T1-1/T2)?