If heat is supplied to an ideal gas in an isothermal process,

According to First law of thermodynamics,

ΔQ=ΔU+ΔW

Where ΔQ=heat supplied to the system

ΔU=change in internal energy

ΔW=work done by the system

For an isothermal process ΔT=0, therefore ΔU=0.

Then,

ΔQ=ΔW

When heat is supplied to the system gas expands i.e. the volume of the gas increases.

We know that,

Work done = force ×displacement

Volume = area ×displacement

Therefore,

Work done=pressure ×volume

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

Pressure =P

Thus, work done by the object W

W=PΔV

During expansion volume increases. Hence, work done will be positive and equals PV.