Consider a gas of triatomic molecules. The molecules are assumed to be triangular and made of massless rigid rods whose vertices are occupied by atoms. The internal energy of a mole of the gas at temperature T is:
The internal energy of one mole of an ideal gas is given by U = (f/2)RT, where f is the number of degrees of freedom. For a non-linear triatomic molecule (assumed to be a rigid rotator), there are:
3 translational degrees of freedom.
3 rotational degrees of freedom. Vibrational modes are generally not c
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