# Two volatile compounds are mixed

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.

#### reising1

##### Full Member
10+ Year Member
What happens when two volatile compounds are mixed? Let's say compound A and B are mixed. Compound A has a vapor pressure of X and Compound B has a vapor pressure of Y. Can any predictions be made about the vapor pressure of the new mixture?

#### navho77

##### Full Member
10+ Year Member
What happens when two volatile compounds are mixed? Let's say compound A and B are mixed. Compound A has a vapor pressure of X and Compound B has a vapor pressure of Y. Can any predictions be made about the vapor pressure of the new mixture?

Yes, predictions can be made using Raoult's Law. The new vapor pressure contributed by A and B separately can be calculated by multiplying the individual, unadulterated vapor pressures by their respective mole fractions in the mixture. The total vapor pressure is just the sum of these partial pressures.

#### reising1

##### Full Member
10+ Year Member
Yes but how about predictions like if the new vapor pressure can be more or less than the individual pure vapor pressures, etc.

#### navho77

##### Full Member
10+ Year Member
Yes but how about predictions like if the new vapor pressure can be more or less than the individual pure vapor pressures, etc.

It would depend on the problem. But the very least that can be said is that the new vapor pressure will always be less than what you would predict by just adding the individual vapor pressures together.

#### reising1

##### Full Member
10+ Year Member
It would depend on the problem. But the very least that can be said is that the new vapor pressure will always be less than what you would predict by just adding the individual vapor pressures together.

Thanks