Enthalpy and specific heat ~ MECHTECH GURU

Enthalpy and specific heat

Enthalpy and specific heat




h = u+ Pv

For an ideal gas u = u(T) only and         PV = mRT and hence h = h(T) only.


Specific heat at constant volume

The specific heat at constant volume is defined as the amount of energy transferred as heat at constant volume, per unit mass of a system to raise its temperature by one degree. That is,

 

Cv = (dq/dT)v

 Specific heat at constant pressure

The specific heat at constant pressure is defined as the energy transferred as heat at constant pressure, per unit mass of a substance to raise its temperature by one degree. That is   

                                                                      Cp = (dq/dT)P

For a constant pressure process

                                                      dq = du + dw 

                                                           = du + Pdv 

                                                           = du+ Pdv +vdP

                               (since dP=0 for a constant pressure process)

     

                                                 Or dq= du+d(Pv) 

                                                          = d(U+ Pv) = dh or dq=dh

                                                   CP  = (∂h/∂T)P

 

The ratio of specific heat (γ) is given by

γ= C P/Cv

 

For mono-atomic ideal gases γ = 1.67 and for diatomic gases γ= 1.4.

Previous
Next Post »