Work done by or on the gas/system

[Naibe Reynoso 2C]

How do we know when work done on or by the gas is negative or positive? How do we know when work done on or by the system is positive or negative?

[Leewon Koo 2K]

When the work is done by the gas (the gas pushes the piston) then work is negative. When the system does work on the gas (the piston compresses the gas) the work done by the system would be negative but the work done by the gas would be positive. I believe in this class we focus on the work the gas is doing so most of our questions should follow the idea of work being done by the gas being negative.

Please let me know if there are any errors :)

[Ethan Liang 1A]

In chemistry, energy put into the system in the form of work and heat are always positive (I mention that because I think it's the opposite for physics, as they're more interested in the effect on the surroundings). So if a gas is expanding, work is negative because it's exerting energy on the surroundings, which is consistent with the equation W=-P∆V, since when volume increases, the overall term is negative. When the gas is compressed, work is positive because energy is put into the system (the overall term would also be positive).