# Homework Help: HELP A question on vapour pressure

1. Oct 16, 2008

### Kudo Shinichi

HELP!!!A question on vapour pressure

1. The problem statement, all variables and given/known data
The vapor pressure of dichloromethane, CH2Cl2, at 0 degree Celsius is 134 mmHg. The normal boiling point of dichloromethane is 40.0 degree Celsius. Calculate its molar heat of vaporization.

2. Relevant equations

3. The attempt at a solution

ln(P_2/134)=(Change of H_vapour/8.314)(1/(0+273)-1/(40+273))
I still have two unknown variables...I should find change H_vapour for this question, but I don't know how to figure out P_2

Thank you for helping me.

2. Oct 17, 2008

### Staff: Mentor

Re: HELP!!!A question on vapour pressure

What does boliling mean?

3. Oct 17, 2008

### Kudo Shinichi

Re: HELP!!!A question on vapour pressure

Boiling (also called ebullition), a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure
Source: wikipedia

4. Oct 17, 2008

### Staff: Mentor

Re: HELP!!!A question on vapour pressure