## surroundings

Boltzmann Equation for Entropy: $S = k_{B} \ln W$

nshahwan 1L
Posts: 100
Joined: Fri Aug 30, 2019 12:18 am

### surroundings

can someone explain how you find surrounding again? I just want a clearer and simpler explanation than the book.

Justin Vayakone 1C
Posts: 110
Joined: Sat Sep 07, 2019 12:19 am

### Re: surroundings

My explanation is sort of modeled off of 4I.9. ΔS of the surr depends on the circumstances. For a reversible process, the system is doing work to push the piston, but the surroundings is giving heat/energy in order to keep internal energy of the system consistent. This means ΔS(surr) = -ΔS(sys) and ΔS(tot)=0. Depending on what variable is changing, use one of the corresponding ΔS equation we've learned to find ΔS(sys), and then multiply a negative to make it ΔS(surr). For an irreversible free expansion, the system isn't doing any work despite pushing the piston up, hence why it is free expansion. There is no heat or energy exchanged from the system to the surroundings, so ΔS(surr)=0.
Last edited by Justin Vayakone 1C on Mon Feb 24, 2020 12:22 am, edited 3 times in total.

peteryim
Posts: 54
Joined: Sat Sep 07, 2019 12:17 am

### Re: surroundings

When the reaction is reversible expansion, delta S total is zero. Thus, delta S surroundings = negative delta S system.
When reaction is irreversible free expansion, delta S total equals delta S of system, and delta S of surroundings is zero.

nshahwan 1L
Posts: 100
Joined: Fri Aug 30, 2019 12:18 am

### Re: surroundings

i guess also how would you go about solving a problem where you aren't given any entropies in the first place? Like this obviously depends on the information given in the question, but i feel like I often don't have enough information to find both. Thank you so much for the explanations tho they were simple and helped.

Mai V 4L
Posts: 111
Joined: Fri Sep 28, 2018 12:23 am

### Re: surroundings

peteryim wrote:When the reaction is reversible expansion, delta S total is zero. Thus, delta S surroundings = negative delta S system.
When reaction is irreversible free expansion, delta S total equals delta S of system, and delta S of surroundings is zero.

Quoting this so I can access it easily

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