## When to use equation [ENDORSED]

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

juchung7
Posts: 44
Joined: Fri Sep 29, 2017 7:05 am

### When to use equation

When would we use this equation -work=-nrt(ln(vf/vi))- versus w=-p(changeinv). I get that we use the first one when the system is in equilibrium, but would a problem explicitly say "this system is in equilibrium/ is reversible?"

Andrea Grigsby 1I
Posts: 60
Joined: Fri Sep 29, 2017 7:03 am

### Re: When to use equation

for the first equation, usually the question says "isothermic" (as in the assigned text book questions)
but it's not going to be on this coming test! :)

Posts: 51
Joined: Fri Sep 29, 2017 7:07 am
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### Re: When to use equation

The first equation is used to find the work done by a reversible process which will not be on the upcoming test. The second equation however, will be on the test as it is the work by expansion.

Kailey Brodeur 1J
Posts: 34
Joined: Thu Jul 27, 2017 3:00 am

### Re: When to use equation  [ENDORSED]

Specifically, the textbook says that the first equation is used for an isothermal, reversible expansion of a gas. As a gas expands, the pressure decreases according to Boyle's Law which is how the equation developed. The second equation is used for non expansion work, so volume change isn't involved.