=

S1 –S2 =

...................

dividing the above equation with T

  = + Cv

this implies that entropy of  a gas is

dS  = + Cv ............................

P/T =R/V

R =PV/T

thus

dS = R  + Cv  .......................................................................

 =R .................................................

S2-S1 = R ln  + Cv ln ....................................

putting the above equation in terms of pressure and volume

                                          S2-S1 = Rln

= (R + Cv)ln + Cv ln

Cp ln + Cv ln

or

 S2-S1= Cp ln + -R ln