## Isothermal expanision and deltaU [ENDORSED]

$\Delta U=q+w$

Liam Maxwell 2E
Posts: 53
Joined: Fri Sep 29, 2017 7:07 am

### Isothermal expanision and deltaU

Why is it that when there is an isothermal expanison, and thus deltaT=0, that deltaU also equals 0?

Vincent Tse 1K
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am
Been upvoted: 1 time

### Re: Isothermal expanision and deltaU

I think it's b/c internal energy is directly related to change in temp.

Forgot where exactly, but there's a derivation somewhere in the book that uses the equipartition theorem and says that molar internal energy is U = 3/2 RT.
Therefore, ΔU = 3/2 RΔT. If ΔT is 0, then ΔU is also 0.

Erica Nagase 1H
Posts: 30
Joined: Sat Jul 22, 2017 3:00 am

### Re: Isothermal expanision and deltaU  [ENDORSED]

Isothermal means that temperature is constant. For an ideal gas (ideal = isothermal conditions), $\Delta U = \frac{3}{2}nR\Delta T$. Because $\Delta T$ = 0, $\Delta U$ = 0,