## Ideal gas expansion

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

Jane Burgan 1C
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Joined: Fri Sep 28, 2018 12:15 am

### Ideal gas expansion

Why is the internal energy of an ideal gas equal to 0 when it expands isothermally and reversibly?

Courtney Quan 1C
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Joined: Fri Sep 28, 2018 12:26 am
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### Re: Ideal gas expansion

When an ideal gas isothermally expands or is compressed, it does so at the same (constant) temperature. Since there is no change in temperature, the gas molecules will continue to move at the same speed and there is no energy change, which is why the internal energy change delta U is equal to zero.

Celine Hoh 2L
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Joined: Fri Sep 28, 2018 12:28 am

### Re: Ideal gas expansion

I understand that q=0 as there is no net heat change. But why isn’t W a negative value as the system has done work to expand?

Carine Tamamian 2B
Posts: 61
Joined: Fri Sep 28, 2018 12:23 am

### Re: Ideal gas expansion

Maybe because the work energy itself is still an amount, disregarding the fact that it's lost or gained. But I'm not sure though, can someone explain?

Karan Thaker 2L
Posts: 75
Joined: Fri Sep 28, 2018 12:26 am

### Re: Ideal gas expansion

I think you're right... the work energy is thought of a value, rather than being gained or loss in this context.