When to use equation [ENDORSED]

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

Moderators: Chem_Mod, Chem_Admin

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! :)

Hammad Khan 2B
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

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.

Return to “Calculating Work of Expansion”

Who is online

Users browsing this forum: No registered users and 1 guest