In this video we are going to derive the expression for work done by a gas,
W=∫PdV. If the gas is heated, it will expand and push the piston up = work done by gas. If the piston is pushed down, on the other hand, the piston does work on the gas and the gas does negative work on the piston. This is an example of how work is done by a thermodynamic system. An example with numbers might make this clearer.

Thumbnail: Work Done By Gas