## First law potential energy

$\Delta U=q+w$

Anna Okabe
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

### First law potential energy

I was reading the textbook and came across one of the thinking points in 8.6. This is about a piston that's moving outward, increasing the volume of the ideal gas. It's asking why there's no potential energy change in an isothermal expansion, even when the molecules are moving apart (hence expansion). I understand that the internal energy does not change because there is no change is potential energy, but I don't get why there is no change.

Lisa Tang 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:05 am
Been upvoted: 2 times

### Re: First law potential energy

I believe that the potential energy doesn't change because this is an isothermal expansion of an ideal gas. Even though molecules are moving apart and therefore separation is increasing, the potential energy remains the same because there are no forces between the molecules.