Question

How many degrees of freedom does a diatomic molecule have at normal temperature?

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

The correct option is C 5

$\text{Number of degree of freedom of a molecule}=3N$
where, N is the number of atoms.
Therefore,
Degree of freedom = 3 $\times$ 2
= 6
In 6, 3 corresponds to translation motion because a molecules can move in all three axis like x, y, z.
Number of vibrational degree of freedom for linear molecule is 3N-5
Therefore,
Vibrational degree of freedom = $3\times 2-5$
= 1
Hence, we have 2 rotational degree of freedom.
At normal temperature, molecule will not have sufficient energy to exhibit vibrational motion.
Therefore, at normal temperature degree of freedom is 5