A similar equation would work for the vibrational contribution, the electronic contribution, and so on. This approximation is useful when N is very large, like around Avogadro's number. Now for some specific models. This is almost right. For reasonable size molecules Q R is usually only a few degrees Kelvin.
Polyatomic molecules have more than one vibrational mode.
Most of what has been given above will work just fine until you try to apply it to chemical reactions, as in when we want to calculate an equilibrium constant. For molecules we select the zero of energy as the separated atoms at rest. This means that all the internal energy states of the molecule have been measured from an energy which is below the zero of energy by an amount equal to the dissociation energy, D e . The energy you calculate or measure depends on what you defined to be the zero of energy. For example, we usually think of the gravitational potential energy of our bodies as being zero, as long as we are on the ground.