## Constant External Pressure

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

Carlos Gonzales 1H
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### Constant External Pressure

One of the equations we are given for work is w=-PexΔV, where external pressure is constant. Will the pressure always be constant or are there instances where the pressure will be different?

Simrina Desar Dis 1H
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Joined: Fri Sep 29, 2017 7:04 am

### Re: Constant External Pressure

Also, why does this pressure have to be constant? What will happen if it varies?

Nancy Dinh 2J
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Joined: Fri Sep 29, 2017 7:07 am

### Re: Constant External Pressure

Carlos Gonzales 1H wrote:One of the equations we are given for work is w=-PexΔV, where external pressure is constant. Will the pressure always be constant or are there instances where the pressure will be different?

For that equation to be used, the pressure has to be constant. However, if the pressure is not constant, then you have a reversible process on your hands and will have to use the the equation w = - nRT ln(Vf/Vi). In Example 8.2, the book solves a problem where pressure is either constant or not.