Let's say we have gas and it expands against a constant external pressure. Is it always doing work, regardless if it's an adiobatic or isothermal or isobaric or reversible or irreversible, etc, process? I'm having trouble with this. It seems like if it expands, it must be doing positive work. But if you take the equation that says work is the negative external pressure times the change in volume, you're going to get a negative answer for the work done by the gas, because the volume goes from low to high. Thanks.