## Reversible/Irreversible Process

$\Delta U=q+w$

Mir Raza 3D
Posts: 19
Joined: Fri Sep 25, 2015 3:00 am

### Reversible/Irreversible Process

Can someone explain what the difference between a reversible and irreversible process is? Does it have any affect on calculations of work?

Aoife Galvin 2D
Posts: 9
Joined: Fri Sep 25, 2015 3:00 am

### Re: Reversible/Irreversible Process

Mir Raza 3D wrote:Can someone explain what the difference between a reversible and irreversible process is? Does it have any affect on calculations of work?

A reversible process is one that can be reversed by an infinitely small change in a variable. For example, if a reaction takes place in a container with a piston (i.e. no constant volume), then it would be reversible if the external pressure and the internal pressure were equal. This is due to the fact that is either one changes even by a little, the piston will move. For instance if the external pressure is increased, then the piston will be pushed down (compression).

An irreversible process is one that can not be reversed by a small change in a variable. Looking at the same example as above, if the external pressure was 2 atm and the internal pressure was 1 atm, a small change in either would not change the direction the piston is moving, it would still move down and compression would occur because the external pressure > internal pressure.

And yes it does have an affect on calculations of work.
For a reversible process, work = -nRT(ln(Volume final/Volume initial))
For an irreversible process, work = -(Pressure external)(change in volume)

And on a separate note, reversible process always do more work than irreversible process.