# Homework Help: Estimate Vapour Pressure

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1. Apr 1, 2016

### annastewert

1. The problem statement, all variables and given/known data
Estimate the vapor pressure of mercury at 25 ∘C (use data from Appendix D from the textbook).

2. Relevant equations
Using the appendix I can find ΔG, ΔH, and ΔS.

3. The attempt at a solution
I have no idea where to start. I think that maybe vapor pressure would be found when ΔG=0, but I'm not certian of that. How could I use this information to find the vapor pressure?

2. Apr 1, 2016

### MexChemE

Given your data, you need to use the Clausius-Clapeyron equation and integrate it. You may use the boiling point of mercury in order to find the constant of integration.

Have you ever used the equation before?

3. Apr 1, 2016

### annastewert

I have not used the equation before but the previous question was to find the boiling point so I do have that

4. Apr 1, 2016

### MexChemE

This is the equation you need to use. It assumes the latent heat of vaporization is constant, however, it would still be possible to integrate the equation if you have an expression for $\Delta H_{vap}$ as a function of temperature.
$$\frac{d \ln P}{dT} = \frac{\Delta H_{vap}}{RT^2}$$
And as I previously said, you may use the boiling point of mercury to find the constant of integration.