Constant Tempreture Process (Isothermal Process)

             A process, in which the tempreture of the working substance remains constant during its expansion or compression, is called constant tempreture process or isothermal process. This will happen when the working substance remains in a perfect thermal contact with the surroundings, so th

at the heat "sucked in' or 'squeezed out' is compensated exactly for the work done by the gas or on the gas respectively. It is thus obvious that in an isothermal process:
    1. there is no change in tempreture.
    2. there is no change in internal energy, and
    3. there is no change in enthalpy.
          Now consider m kg of a certain gas being heated at constant tempreture from an intial state 1 to final state 2.
    Let                 p1v1 and T1 = Pressure, volume and tempreture at the intial state 1, and

                          p2v2 and T2 = Pressure, volume and tempreture at the final state 2.