## entropy of surr vs entropy of system vs total entropy

$\Delta S = \frac{q_{rev}}{T}$

vanessas0123
Posts: 100
Joined: Wed Sep 11, 2019 12:17 am

### entropy of surr vs entropy of system vs total entropy

What's the difference between the entropy of the surrounding, system, and total entropy? And how would you find these values in isothermal reversible and irreversible expansions?

Vincent Leong 2B
Posts: 207
Joined: Fri Aug 09, 2019 12:15 am

### Re: entropy of surr vs entropy of system vs total entropy

delta s total refers to the universe and the delta s system + surr are self explanatory (your system and whatever you define as your surroundings). An example is a cup and a bench. The cup is my system and its on my surroundings (the bench). The key concept is that for a reversible system delta S total or delta S universe is 0. For an irreversible process, delta S surr is 0.

Abby Soriano 1J
Posts: 103
Joined: Sat Aug 24, 2019 12:16 am

### Re: entropy of surr vs entropy of system vs total entropy

Vincent Leong 2B wrote:delta s total refers to the universe and the delta s system + surr are self explanatory (your system and whatever you define as your surroundings). An example is a cup and a bench. The cup is my system and its on my surroundings (the bench). The key concept is that for a reversible system delta S total or delta S universe is 0. For an irreversible process, delta S surr is 0.

Can you further explain why delta S total is 0 only under reversible conditions? What accounts for this difference?

Vincent Leong 2B
Posts: 207
Joined: Fri Aug 09, 2019 12:15 am

### Re: entropy of surr vs entropy of system vs total entropy

delta S of the universe is 0 for reversible rxns bc the reversilble rxns can go back to their initial states. If you think of delta, its a measure of change. If your final and initial state are identical, there is no measure of change bc technically, you ended where you started. Therefore there is no delta and thus the delta S of universe is 0.