# Thermodynamics: finding work done

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1. Apr 6, 2015

### Frozen

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

In a closed system 0.4kg of gas at 374K is expanded isothermally and reversibly from 1MPa pressure to 300kPa. Given that Cv = 718j/kg and R = 287j/kg, determine the work done.

2. Relevant equations
Not sure? I guess W = p*V?

3. The attempt at a solution
I honestly don't know how to solve this one.

2. Apr 6, 2015

### Frozen

NB: I don't want anyone to do this for me, in case anyone thinks I'm trying to cheat. I just want someone to point me in the right direction because I honestly don't know where to begin figuring this out.

3. Apr 6, 2015

### Staff: Mentor

What is the equation for the differential work dW done by a gas on its surroundings in terms of the external force per unit area Pext and the differential change in volume dV? For a reversible process, how is the external force per unit area Pext related to the gas pressure?

Chet

4. Apr 7, 2015

### DrewHizzy

Chet, I'm sure this is an algebra based physics question, not calculus.

5. Apr 7, 2015

### Staff: Mentor

Really. What makes you think so? This problem can not be solved correctly unless PdV is integrated, or the person has a formula for the result of the PdV integration.

Chet