Sign Convention for Work

  • Work done the system is taken as positive; Work done by the system is taken as negative.
  • With the above sign convention, the formula for work is taken a:


and



 

The amount of work involved is equal to the area under the curve. In compression, DV is negative and the work done on the gas,  W=-PDV will be positive.

In expansion, DV     is positive, and the work done ON the gas W=-PDV       is negative, i.e. work is actually done BY the gas.




P is constant


P varies



W depends on the way the system goes from one state to another