Homework Help: ChemE: vapor pressure and condensation

1. Nov 20, 2012

GreatEscapist

1. The problem statement, all variables and given/known data
A gaseous mixture containing 0.190 mol fraction of carbon tetrachloride (CCl4) and 0.810 mol fraction of dry air is initially at 62.0°C and 1141 mmHg. If this mixture is cooled at a constant pressure, at what temperature does the CCl4 first start to condense? I already did this problem

At what temperature would 56.0% of the CCl4 condense?

2. Relevant equations
Partial pressure = p*(T)
log10(p*)= A + (B/(T+C))
I'm sure there are more I'm supposed to use

3. The attempt at a solution

After solving for the original problem, for the second, I know that I need to find how many moles are condensed...but I don't know how to do that. Or what to do after that, or with that information.

2. Nov 21, 2012

rude man

Not sure how the dry air enters the problem, but disregarding that, once the CCl4 starts to condense, it is impossible to further reduce the temperature of the (two) CCl4 phases at constant pressure until the CCl4 is saturated liquid. That should answer your question ...

3. Nov 21, 2012

Staff: Mentor

Take as a basis one mole of gas. Then the number of moles of CCl4 is 0.19, and the number of moles of air is 0.81. If 56% of the CCl4 condenses, how many moles of CCl4 liquid is formed, and how many moles of CCl4 remain in the gas phase? What is the total number of moles remaining in the gas phase (air plus CCl4)? At that point, what is the mole fraction of CCl4 in the gas phase? Since the total pressure remains 1141 mm Hg, what is the partial pressure of CCl4 in the gas phase? What is the equilibrium temperature at this vapor pressure of CCl4?