An ideal gas goes from the state i to the state f as shown in the figure. The work done by the gas during the process.


Since the graph between P and T is a straight line passing through the origin, therefore PT.


P can only be proportional to T when the volume is kept constant. This can be easily proved from the ideal gas equation which is


PV=RT


Since R is already a constant, if volume also becomes constant then PT.


Constant volume implies ΔV=0.


We know that,


Work done = force ×displacement



Volume = area ×displacement


Therefore,


Work done=pressure ×volume


Let change in the volume of system = ΔV = V2-V1


Pressure =P


Thus, work done by the system W


W=PΔV


For ΔV=0, W=0.

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