## Irreversible Expansion

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

Abigail Urbina 1K
Posts: 102
Joined: Thu Jul 27, 2017 3:01 am

### Irreversible Expansion

I know that Dr. Lavelle went over this in lecture yesterday a little bit, but can someone please explain to me exactly what an irreversible expansion is? And why is it irreversible? If I understand this correctly, I know that a reversible expansion can be reversed through an infinitesimal change (small fluctuation) in the internal and external pressures. Also, work is a reversible process when the system is at equilibrium.

Can someone please give a more specific conceptual definition of irreversible expansion and how it differs with reversible expansion?

Katie Lam 1B
Posts: 52
Joined: Fri Sep 29, 2017 7:06 am

### Re: Irreversible Expansion

Irreversible expansion is irreversible because pressure is reduced much more quickly than in a reversible reaction, where the pressure changes very slowly and maximum work is done. In irreversible processes, the system is not in thermodynamic equilibrium the entire time while in reversible processes, it is.

Sarkis Sislyan 1D
Posts: 31
Joined: Thu Jul 27, 2017 3:00 am

### Re: Irreversible Expansion

Dr. Lavelle gave the example in lecture of a piston with internal pressure of 2 atm and an external pressure of 1 atm. With nothing being done to keep the piston in place (such as a pin being inserted), the internal pressure would push up against the weaker external pressure in a sudden movement. This is an irreversible reaction. A reversible reaction instead would have both the internal and external pressure be equivalent at 2 atm. In this case, there would need to be many many small movements in order to raise the piston. In this case, the reaction can be reversed by making infinitesimally small changes to factors such as pressure, but in an irreversible reaction, this is not the case.

Yeyang Zu 2J
Posts: 58
Joined: Fri Sep 29, 2017 7:06 am

### Re: Irreversible Expansion

First, reversible process is one that can be reversed by an infinitely small change in infite-small change
for example, 2 systems are both under 2 atm pressure, they could push/pull each other with a tiny small change in volume, it works the same for both directions

however, if the 2 system are one 1 atm and another 2 atm, push/pull to two different directions representing two different results due to the pressure difference