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## Homework Statement

Hello, new here! I have a question regarding reversible or irreversible expansions in regards to figuring which equation is needed to figure out work, W. For starters, here is the question:

One mole of an ideal monatomic gas is expanded from an initial state of 3 atm and 500 K to a final state of 1 atm and 300 K. Calculate w, q and ∆U.

Note: Approximate 1 atm 1 x 105 Pa. For an ideal monatomic gas, Cv = 3R/2 and Cp = CV + nR.

So below, I know of two different equations for w,

## Homework Equations

dw = − pex × dV for an irreversible expansion and

Wrev =−nRT Vf ∫ Vi 1/v dV=−nRTln Vf/Vi for a reversible expansion.

## The Attempt at a Solution

I have looked at a few factors in the question, most research points to w = -Pex X dv but no explanation as to why. I also know it is not isothermal or isobaric based on the info above.[/B]

Since the question did not specify reversible or irreversible, which should I use and how should I know how to understand for future reference? Thanks for the help!

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