## When to use w= -P∆V

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Remi Lathrop 1G
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

### When to use w= -P∆V

Does your system have to be at constant pressure and isothermal in order to use the equation w = -P∆V? I've come across a few problems where I tried to use it but got it wrong, was wondering if the system changing temperature is the reason I'm missing these questions?

Dylan Davisson 2B
Posts: 50
Joined: Thu Jul 27, 2017 3:00 am
Been upvoted: 2 times

### Re: When to use w= -P∆V

For the equation w = -P∆V to work properly, it just has to be under constant external pressure. Temperature does not affect this part of the equation at all, because it deals with work. But if you are trying to calculate the change in internal energy, you have to make sure that you add the heat applied to the work (deltaU= q + w).