C_(v) value of He isalways 3 R//2 but C_(v) value of H_(2) is 3R//2 at low temperatureand5R //2 at moderate temperature and more than 5R//2 at higher temperature . Explain in two or threelines.

C_(v) value of He isalways 3 R//2 but C_(v) value of H_(2) is 3R//2 at

1.	C_(v) value of He isalways 3 R//2 but C_(v) value of H_(2) is 3R//2 at low temperatureand5R //2 at moderate temperature and more than 5R//2 at higher temperature . Explain in two or threelines.
Answer» Solution :Refer to ART,page. He is a monoatomic gas. It has only THREE translational DEGREES of freedom. Hence, its energy per mole`= ( 3)/(2) RT:. C_(v) = ((DELTAU)/(DELTAT))_(v) (3)/(2)R` `H_(2)` is a diatomic molecule. It has not only translational motion but also has rotationaland vibrational motion. At moderate temperature,contribution by vibrational motion is negligible but as ithas two rotational degrees of motion ( being a linear molecule), contribution to energyby rotational degrees `2 xx (1)/(2) RT`. Hence total energy `= (5)/(2) RT` and therefore, `C_(v) = ( 5)/(2) R`. On increasing the temperature, contribution from vibrational degrees also starts and hence `C_(v)gt (5)/(2) R`