## Expansion/Contraction

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

MorganYun1H
Posts: 59
Joined: Thu Jul 13, 2017 3:00 am

### Expansion/Contraction

when the book says that internal energy equals q when no expansion or contraction take place, does that mean volume stays the same? In other words, are expansion/contraction referring to whether the volume increases/decreases, respectively?

Nehal Banik
Posts: 64
Joined: Thu Jul 13, 2017 3:00 am

### Re: Expansion/Contraction

What the book means when the change in internal energy equals q which is the heat transferred to a system or released, when it says no expansion or contraction occurs in the form of work, therefore when there is no work happening through expansion or contraction, then the internal energy should equal the heat of the system.

Ryan Sydney Beyer 2B
Posts: 82
Joined: Fri Sep 29, 2017 7:07 am
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### Re: Expansion/Contraction

Another way of thinking about this type of problem is from the perspective of work. If there is no expansion / contraction on the system then work must be zero since there is no work being done on the system and the system is not doing work. Looking back to the equation, Delta U = q + w, then if work is 0, Delta U = Delta q.