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### Work done by expansion

Posted: Sun Feb 03, 2019 11:50 pm
When calculating work, the equation is w= -p *deltaV, what is the reason behind pressure being negative?

### Re: Work done by expansion

Posted: 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.

### Re: Work done by expansion

Posted: 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.

### Re: Work done by expansion

Posted: 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.