Explain sign convention of work.
Explain +Wand -W.

Explanation

When a gas expands against a constant pressure, `P_("ex")` changing the volume from initial volume `V_(1)` to final volume `V_(2)`,
Change in volume, `DeltaV = V_(2) - V_(1)`
The mechanical work `= W = - P xx DeltaV = - P_(ex)(V_(2) -V_(1))` (By IUPAC convention).
(1) During expansion `V_(2) gt V_(1)` The work is said to be performed by the system on the surroundings . This result in the decrease in the energy of the system. Hence the work is negative , i.,e. W is - ve.
(2) During compression , `V_(2) ltV_(1)` The work is said to be preformed on the system by the surrounding . This results in the increase in the energy of the system. Hence the work is positive i.e., W is +ve.