## Reversible Processes

$\Delta U=q+w$

Julie Steklof 1A
Posts: 50
Joined: Thu Jul 13, 2017 3:00 am

### Reversible Processes

Why does a system being at equilibrium mean that it is a reversible process?

Rohan Chaudhari- 1K
Posts: 32
Joined: Fri Sep 29, 2017 7:06 am

### Re: Reversible Processes

A reversible process is one where you can go backwards in the process at any time without increasing entropy. This can only happen during an equilibrium.

Kate Zeile 2D
Posts: 39
Joined: Sat Jul 22, 2017 3:01 am

### Re: Reversible Processes

When a system is at equilibrium, an infinitesimal change in a variable can cause the process to reverse. I do not know if this correlates exactly, but I like to think of it this way:
Let's say you have two piles of rocks that weigh the same amount and are each placed on one side of a see-saw. The see-saw would be in balance since the rock piles weigh the same (this represents a system at equilibrium). If you took a tiny pebble out of one of the piles (therefore making an infinitesimal change), then the see-saw would shift in one direction. Since such an infinitesimal change causes the process to shift, it is a reversible process.
Now imagine you have two piles of rocks on the see-saw again, but one pile is heavier than the other one, so the see-saw is already tilting to one side (this represents a system not at equilibrium). If you took a tiny pebble out of one of the piles, the see-saw wouldn't shift because making such a tiny change does not affect the system since one pile is heavier than the other. This would be an irreversible process.