Question

$C_v$ for $O_2$ is $\frac{ 5}{2}$ R with increase in temperature it becomes $\frac{ 7}{2}$ R due to a

• A. translational motion
• B. rotational motion
• C. vibrational motion
• D. None of the above

Answer 1

Answer: (C)

vibrational motion

Answer 2

Oxygen is a diatomic gas and hence has 5 degree of freedom 3 translational and 2 rotational.
As t e eat is given to oxygen $C_v$ increases rom $\frac{ 5 R}{2} \, to \, \frac{ 7 R}{2}$
Hence, internal energy ( $\triangle U = n C_v \triangle T)$ increases. With the increase in internal energy the atoms within the molecule may also vibrate with respect to each other. In such case the molecule will have an additional degree of freedom due to vibrational motion.