## Midterm 4a

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

CameronJohari1J
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### Midterm 4a

How are we supposed to identify that this expansion is irreversible or reversible? Are there any hints or clues in the problem that imply one type of expansion over the other? Thank you in advance.

Melissa Per 2J
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### Re: Midterm 4a

Could you post the question from the midterm here please?

Kevin Ru 1D
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### Re: Midterm 4a

The question is: A piston containing 0.10 mol of nitrogen gas at 298 K has an initial volume of 2.24 L and
undergoes an expansion against 0.5 atm external pressure until its volume doubles.
Calculate the work involved in Joules.

The key here is that it states there is an external pressure of 0.5 atm. We can assume from this that external pressure does not change and therefore, the process is irreversible. Irreversible expansion is against a constant external pressure while reversible expansion of an ideal gas has a pressure that keeps changing.

AtreyiMitra2L
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### Re: Midterm 4a

Because we know its constant external pressure, we automatically know that its undergoing an irreversible expansion.

Jiun Yue Chung 2I
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Joined: Fri Sep 29, 2017 7:06 am

### Re: Midterm 4a

I think you can identify it as irreversible because for that question, it says the external pressure is constant. For reversible changes, however, external pressure is ever so slightly changing.

Pooja Nair 1C
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### Re: Midterm 4a

Because they don't give you a different pressure value, you can assume that external pressure is constant. In the case of constant external pressure, the expansion is irreversible

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