00:01
If we are assuming ideal behavior, then we can use rayultz law.
00:05
Rayults law states that the total pressure provided at 331 millimeters of mercury is going to be equal to the mole fraction of a, which will be 1 .2 moles of a, divided by the total moles, which is going to be 3 .5, 1 .2 plus 2 .3, multiplied by the vapor pressure of pure a, which we don't know, plus the mole fraction of b, which will be 2 .3, divided by 3 .5, multiplied by its pure vapor pressure.
00:52
And then in a second situation, we have a total vapor pressure of 347, when we add an additional mole of b.
01:04
Means we still have 1 .2 moles of a but now the total moles is 4 .5 and then we've got p knot and then plus now we've got 3 .3 moles of b for a total of 4 .5 and you can see we have two equations and two unknowns.
01:32
So now we need to combine these two equations.
01:35
To do that let's see if we can change this equation into an expression for the vapor pressure of pure a as a function of the vapor pressure of pure b...