# Physical Chem review

1. Jan 22, 2017

### IoFawkes

1. The problem statement, all variables and given/known data
Calculate Work(w) when 6.5L of an ideal gas at an initial pressure of 34.3atm is expanded or compressed isothermally to a final volume of 34.3L reversibly. Answer in J

2. Relevant equations
PV=nRT
P1V1=P2V2
w=-nRT In(V2/V1)

3. The attempt at a solution
Using w=-nRT In(V2/V1)
I'm not given mols or T, I know T=constant, since it's isothermal
Can I use PV=nRT and substitute (PV) in for (nRT) in the equation: w=-nRT In(V2/V1) ?
If so, what should I use for values of P and V? Final/Initial/delta?

Io

PS: This may be in the wrong place, the boundary seems unclear in Chem/Phys or Phys/Chem studies.

2. Jan 22, 2017

### TSny

Welcome to PF!
Yes
How does PV in the initial state compare to PV in the final state?

3. Jan 22, 2017

### IoFawkes

P1V1=P2V2 so it doesn't matter which I use as long as P and V are both initial values, or final values. Correct?
EDIT: Except it's asking for work done, so would it be the Change in Pressure and Volume?
Io

Last edited: Jan 22, 2017
4. Jan 22, 2017

### TSny

Yes
nRT is a constant for an isothermal process. At any point along the process, nRT has the same value. The ideal gas law tells us that for any state, nRT = PV. So, nRT for the isothermal process equals PV evaluated for any state along the isothermal process.

nRT would not correspond to a change in PV.

5. Jan 22, 2017

### IoFawkes

Ah, that makes sense, thanks! How wonderful a change in perspective.

Io