And we have also looked at how to get the absolute entropy, the third law entropy.
Similar procedure, we begin integrating from zero kelvin, heat capacity divided
by temperature up to a phase change, then the liquid up to a phase change.
There may be multiple solids, by the way, there could be other phase changes in
there. But in any case we have a way, and video
7.3 was where we did this for entropy, we have a way to assemble the numbers needed
to add together to answer the question, how much free energy is there compared to
at zero kelvin? So, let's just look at an example, and in
particular, let's take benzene as an example.
And we'll look at the free energy at 1 bar pressure.
So remember that dG is equal to minus SdT plus VdP.
And I put this up here just because it's sort of a sanity check, what do we expect
to happen to the free energy? Well.
As the temperature increases, so dT, a positive value, it's getting larger,
multipliying a negative quantity, and the absolute entropy is a positive value, so
we get that G should be getting more and more negative as the temperature goes up,
from this term. We're not saying much about this yet, but
actually, let's not worry about that for a moment.