constant external pressure


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Karyn Nguyen 1K
Posts: 72
Joined: Fri Apr 06, 2018 11:04 am

constant external pressure

Postby Karyn Nguyen 1K » Tue Feb 12, 2019 3:35 pm

How do we know if the external pressure is constant in order to use ?

Shally Li 2C
Posts: 30
Joined: Fri Sep 28, 2018 12:22 am

Re: constant external pressure

Postby Shally Li 2C » Tue Feb 12, 2019 3:40 pm

It should either be given or you could be given enthalpy. The definition of enthalpy is heat at constant pressure, so if you're given enthalpy, you know pressure is constant.

Fayez Kanj
Posts: 62
Joined: Fri Sep 28, 2018 12:18 am
Been upvoted: 1 time

Re: constant external pressure

Postby Fayez Kanj » Tue Feb 12, 2019 5:02 pm


In most cases, this is explicitly stated in the problem ("against a constant pressure" of ...). However, if it is not, then you could try to infer. If the volume changes, then this is most likely going to be a reaction that involves a change in pressure (since we use w=nRTlnV2/V1). Isobaric also means constant pressure.

Hope this helps :)

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