Entropy Changes

[@shuchenzhou1730]

what would be the enthalpy change if we got a varying pressure?

[@mortezakhoshbin]

thanks dear Dr.stuart I have found a little mistake in the calculations of Flory-Huggins mixing entropy equation that results in a differnt equation that i found it. I need someone to help me varify my developed equation by real datas. It will be honor if you cooperate to make a paper from it. if you are interested please allow me to email you reasons to my claim.thank you

[@PhysicalChemistry]

Flory-Huggins is a great example of the sort of lattice models considered in some of the earlier lectures. (See kzbin.info/www/bejne/rGi4q4apl610o9k) Hopefully I will be able to post a video on the Flory-Huggins polymer model sometime in the future. I do have a video posted on the entropy of mixing (see kzbin.info/www/bejne/aIXFfJ-Oi7x0gJY), but it is for gases / fluids, and ideal polymer solutions are slightly different.

[@hershyfishman2929]

1:32 Why does being isothermal mean that dU is 0? Can't potential energy still change even if it's isothermal?

[@PhysicalChemistry]

That is true because we are talking specifically about an ideal gas. For an ideal gas, U = ³/₂ NkT, which was obtained here: kzbin.info/www/bejne/qXqZemaAj5mnhpY You're certainly correct that things other than temperature can affect the internal energy, for many substances. But for an ideal gas, the only form of energy it has is kinetic energy, so U depends on temperature and nothing else.

[@jorjereyes9491]

What does the horizontal line over the d mean?

[@PhysicalChemistry]

That indicates that dq and work are inexact differentials, rather than exact differentials like dU. This is related to the fact that q and w are path functions, while U is a state function. Here is the earlier video on inexact differentials: kzbin.info/www/bejne/ZqfOknWtp52Cg9U

[@thepirate6521]

awesome video, greetings from Poland!

[@PhysicalChemistry]

Cześć and thanks!