## Irreversible Expansion vs. Reversible Expansion

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

Alexia Joseph 2B
Posts: 56
Joined: Thu Jul 27, 2017 3:01 am

### Irreversible Expansion vs. Reversible Expansion

I'm still kind of confused going, how can you tell if something is expanding irreversibly vs. reversibly?

Sean Monji 2B
Posts: 66
Joined: Fri Sep 29, 2017 7:06 am

### Re: Irreversible Expansion vs. Reversible Expansion

Usually the problem will tell you directly, but if not: If the problem gives you a constant external pressure, the expansion should be irreversible; but if the pressure is increasing in miniature steps, the expansion should be reversible.
Irreversible has a noticeable difference between the internal and external pressure; reversible has a infinitely small difference in internal and external while the external pressure is decreasing in small steps.
Hope that helps

Sally Nason - 1K
Posts: 40
Joined: Fri Sep 29, 2017 7:05 am

### Re: Irreversible Expansion vs. Reversible Expansion

Since you use the equation w = -P*deltaV for irreversible expansion, you would likely be given the pressure or the change in moles to use for substitution with PV = nRT. For reversible expansion, we use the equation w = -nRT*ln(V2/V1) so you would likely be told it is isothermal and the moles would not change. These are just little things to look for to help determine which equation to use.