## Irreversible expansion

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

William Lan 2l
Posts: 73
Joined: Fri Sep 29, 2017 7:07 am

### Irreversible expansion

I understand that in an irreversible expansion, the system is not in equilibrium. But what does this conceptually mean? And why is it irreversible?

Matthew Lee 3L
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

### Re: Irreversible expansion

The system is not in equilibrium in an irreversible expansion, because unlike in a reversible expansion, the pressure is reduced quickly, allowing the gas to expand and do work on the external pressure. I'm not entirely sure why it is called irreversible though.

Andrew Nguyen 2I
Posts: 68
Joined: Fri Sep 29, 2017 7:07 am

### Re: Irreversible expansion

I believe it is called irreversible because the large change in volume in a quicker process, makes it difficult to compress the gas/system back to its original volume. In a reversible process the external and system pressures are very close in value at each step, so the change in volume is so small - that the work required to compress the gas back is much easier and more reversible in a sense.

Mitch Mologne 1A
Posts: 74
Joined: Fri Sep 29, 2017 7:04 am

### Re: Irreversible expansion

A gas prefers to be at a lower pressure, and thus a higher volume. If it is able to do work to get to a lower pressure, it will stay there, making the process irreversible.

Yu Chong 2H
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: Irreversible expansion

Irreversible means that the direction of expansion/contraction will not be changes by a tiny amount of change in external pressure. For example, if the gas of 1 atm is expanding against an external surrounding of 1 atm, if the outside pressure increases even a little bit, the gas will go from expanding to contracting.