different ways to calculate w


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Chew 2H
Posts: 34
Joined: Fri Sep 29, 2017 7:05 am

different ways to calculate w

Postby Chew 2H » Sun Feb 11, 2018 10:53 pm

when do we use -PdeltaV and when do we use -nRTln(V2/V1) in calculating w? What's the difference between the two?

Farah Ahmad 2A
Posts: 30
Joined: Thu Jul 27, 2017 3:00 am
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Re: different ways to calculate w

Postby Farah Ahmad 2A » Sun Feb 11, 2018 10:57 pm

Generally you would use w=-nrtln(v2/v1) when it is an isothermal, reversible reaction.

Abigail Yap 2K
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

Re: different ways to calculate w

Postby Abigail Yap 2K » Sun Feb 11, 2018 10:59 pm

Hi,

I believe the first equation is used when the system is at equilibrium (constant pressure) and the second is used when the pressure is changing.

Luis De La Cruz 1H
Posts: 37
Joined: Fri Sep 25, 2015 3:00 am

Re: different ways to calculate w

Postby Luis De La Cruz 1H » Sun Feb 11, 2018 11:50 pm

Indeed, you would use the first equation for instances in which pressure is constant, since the equation itself seems to tell you there is no change in pressure, only a change in volume, hence the missing delta before pressure. While the second equation is a derived equation (which you don't need to know the derivation of) that is used for instances in which pressure is not maintained at a constant.

AtreyiMitra2L
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Re: different ways to calculate w

Postby AtreyiMitra2L » Sun Feb 11, 2018 11:54 pm

We use the former with constant pressure and the latter when its not constant pressure. The first is irreversible expansion and the latter is irreversible, isothermal expansion.


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