1 mol of a gas occupying 3 liter volume is expanded against a constant external pressure of 1 atm to a volume of 15 liter. Calculate work done by the system.

Since work is done against constant pressure and, thus, irreversible.'. Work done under irreversible processWirr =−Pext V2−V1=−1×(15−3)=−12 liter atm =−12×1.987×4.1840.0821 joule =−1.215×103 joule.