# Dissociation Energy (Modern physics)

1. Apr 27, 2012

### Pedro Roman

1. The problem statement, all variables and given/known data

Hello, the question is, does the binding energy of a molecule is greater than or equal to the dissociation energy?

2. Relevant equations

A molecule exists because its energy is less than that of the system of separate noninteracting atoms:

Mc²∠Ʃ mi

Here M is the mass of the molecule, mi is the mass of the ith atom constituting the molecule, and c is the speed of the light.

The total potential energy U of two atoms the system often approximated by the expression

U = -A/rn + B/rm

where r is the intermolecular separation distance between the two atoms, A and B are constant, and n y m are small integers.

3. The attempt at a solution

Because the potential has an absolute minimum Umin when the intermolecular distance is small, the energy of the molecule is less than the energy of the separated atoms. This means that the energy of dissociation is -Umin, ie, when U = 0, since the atoms before forming molecule were far away from each other, the energy was larger than zero, therefore dissociation energy is less than the binding energy. Is my reasoning correct?

Thanks a lot.

Last edited: Apr 27, 2012