[xxangelxwingsxx]

I was just wondering when using the equipartition principle to work out Cv and Cp why does Cv=Cp+R only apply for the translational motion (Cv=3/2R; Cp=5/2R), why do we not add R to the vibrational ({3N-5}R for linear/ {3N-6}R for non-linear) and rotational (R for linear, 3/2R for non-linear) contributions?

Thanks

[TIGERHULL]

You can think of it in differential terms.

Cv = dU/dT

Cp = dH/dT

H = U+pV = H +nRT

Which wwhen differentiated with respect to T, yields the value of U +nR.

[Jorriss]

Kinetic Molecular Theory only considers ideal gasses which only consider translational motion. Those vibrational and rotational degrees of freedom are not part of the theory and Cp-Cv=R is only for an ideal gas.

[xxangelxwingsxx]

Thanks