Question

The Clapeyron-Clausisus Equation is ln(P2/P1) = dHvap/R [(1/T1)-(1/T2)]. Assuming that dHvap doesn't change with the temperature, this equation relates the change in vapor pressure and temperature to a substances enthalpy of vaporization (R is the molar gas constant). Use this relationship and the fact that dHvap of water at 25C is 43.99 kL/mole to calculate the vapor pressure of water at 5, 25, 50, 95 C. Results should be in order from least to greatest and in Torr.


(A) 21.2, 39.6, 86, 731

(B) 5.92, 39.6, 92, 601

(C) 5.92, 21.2, 83.9, 622

(D) none of these

Answer 1

The one piece of data you don't have in the problem (no one ever puts this in and that's the secret) is you are supposed to recall that the boiling point occurs when the vapor pressure of a liquid equals atmospheric pressure. The piece of data you need is pH2O @ 100 C = 760 torr.
Substitute this and the other data and solve.

Answer 2

I don't know how to solve it

Answer 3

Plug in the numbers and post it.

Answer 4

plug what into where? my teacher hasn't explained anything relating to this problem so I have no idea what to do.

Answer 5

It looks obvious to me and I would think is is obvious to you. p1 is the pressure 1, p2 is pressure 2, dHvap must be heat vaporization, T1 and T2 surely must be temperatures. dHvap must go in with units of J, T1 and T2 must be in Kelvin, P1 and P2 can be in any unit but both must be in the same unit.