4. A cylinder with an initial volume of 15.0L is fitted with a frictionless piston and is filled with 2.00 mole of an ideal gas at 25C. Assume that the surroundings are large enough so that if heat is withdrawn from or added to the system, the temperature of the gas does not change. (a) The gas expands isothermally and irreversibly from 15.0L to 30.0L as the external pressure changes instantaneously in a single step from 3.26atm to 1.63atm. Draw a PV diagram illustrating this process, then calculate q and w.(w=P8xtV)