# Calculate the entropy changes of the system and the surroundings

1. May 14, 2016

### sara lopez

1. The problem statement, all variables and given/known data

Calculate the entropy changes of the system and the surroundings if the initial and final states are the same
as in part a ( part a= 2.000 mol of neon (assume ideal with CV,m _ 3R/2) is expanded isothermally at 298.15K from 2.000 atm pressure to 1.000 atm pressure and is then heated from 298.15K to 398.15K at a constant pressure of 1.000 atm) , but if the gas is expanded irreversibly and isothermally against an external pressure of 1.000 atm and then heated irreversibly with the surroundings remaining essentially at equilibrium at 400 K.

2.000 mol of neon

CV,m = 3R/2

T1= 298.15K

T2= 400 K.

P1= 2.000 atm v1= 24,4 L

P2=Pext = 1.000 atm v2= 48,89L

2. Relevant equations

3. The attempt at a solution

I think im getting a bit confused here because the problem asks for the entropy changes of the system and the surroundings, but how to calculate the surroundings for irreversibly?

ΔS u = ΔS sist + ΔS surro

ΔSsurroundings = qsurroundings /Tsurroundings = − q system /T surrounding

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2. May 14, 2016

### Staff: Mentor

In the irreversible case, the change in entropy of the system is the same as for the reversible case. To find the change in entropy of the surroundings for the irreversible case, you must first determine the amount of work done in the first step. If the final temperature is equal to the initial temperature in the first step, what is the amount of heat transferred in the first step? What is the amount of heat transferred in the second step?