Work done by expansion

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Alondra Olmos 4C
Posts: 32
Joined: Fri Sep 28, 2018 12:21 am

Work done by expansion

Postby Alondra Olmos 4C » Sun Feb 03, 2019 11:50 pm

When calculating work, the equation is w= -p *deltaV, what is the reason behind pressure being negative?

Mukil_Pari_2I
Posts: 87
Joined: Fri Sep 28, 2018 12:29 am

Re: Work done by expansion

Postby Mukil_Pari_2I » Sun Feb 03, 2019 11:52 pm

When a gas expands against external pressure, it has to to transfer some of its energy over to the surroundings so it reduces its overall energy because of its negative work.

chaggard
Posts: 37
Joined: Fri Sep 28, 2018 12:19 am

Re: Work done by expansion

Postby chaggard » Tue Feb 05, 2019 9:12 pm

Pressure can never be negative, however according to the first law of thermodynamics, the negative sign is in there because the energy lost is gained by the system.

Stevin1H
Posts: 89
Joined: Fri Sep 28, 2018 12:17 am

Re: Work done by expansion

Postby Stevin1H » Wed Feb 06, 2019 12:17 am

This is not saying that the pressure is negative. The negative is in this equation because if the volume of the system is compressed, delta V (which is Vf-Vi) will be a negative value. This negative value of delta V and the negative value in the equation will become positive since two negatives become a positive. This makes the work value positive, which makes sense because the system is being compressed so work is being done on the system.


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