00:01
When we think about vapor pressure, we have to remember that vapor pressure is essentially an equilibrium.
00:05
Vapor pressure is the pressure exerted by a vapor onto its own liquid state.
00:11
So essentially we have liquid molecules at the surface escaping into the gas phase, and then in turn we have gas particles above the liquid, exerting a pressure onto the surface.
00:23
So because our vapor pressure is an equilibrium, we can use this concept that our kp, our equilibrium constant is equal to our vapor pressure.
00:37
Super simple.
00:39
So because we know this, we can use our gibbs free energy equation here, where we have delta g standard is equal to negative universal gas constant times temperature times the natural log of our kp.
00:53
So let's assemble all the elements of this equation.
00:57
To find our delta g standard, we can use the data in appendix to allow us to find the free energies of formation for our products minus our reactants.
01:08
So we have negative 228 .6 for our gas water and that's going to be in kilojoules per mole minus negative 237 .2 kilojoules per mole and that will give us a delta g standard of 8 .6 kilojoules per mole.
01:41
So we know that our universal gas constant because it's a constant, it's always the same.
01:47
So we have 8 .314 joules per mole kelvin times kelp.
01:56
And then we're at standard temperature here, so we have 298 kelvin.
02:04
So before we plug into our equation, we want to do a quick unit check here.
02:09
I see that we have joules here...