How is energy released when a chemical bond is formed? Chemical reactions are classed as endothermic or exothermic.

Defn: exothermic


  (of a reaction or process) accompanied by the release of heat.


The heat is released when the chemical bonds in the product are formed.

Defn: heat


  heat is energy in transfer to or from a thermodynamic system, ... The
  mechanisms include conduction, ...; or radiation between separated
  bodies; or ....


So, I have three questions:

1 - if the heat is released via conduction, is this equivalent to an increase in the kinetic energy of the product(s) compared to the kinetic energy of the reactant(s)?  Also, how does the formation of a chemical bond produce kinetic energy?

2 - if the heat is released via radiation, how is radiation created in the formation of a chemical bond?

3 - are conduction and radiation the only forms of heat transfer when a bond is created?

Edit - to clarify the question - the issue is addresed in the OPENSTAX AP chemistry text - which covers one example of 2 H atoms coming together to form H2 in detail as follows:


  When the atoms are far apart ..... by convention the sum of their
  energies is 0. As the atoms move together their orbitals begin to
  overlap.  Each electron begins to feel the attraction of the nucleus in
  the other atom.  In addition, the electrons begin to repel each other,
  as do the nuclei.  While the atoms are still separated, the
  attractions are slightly stronger than the repulsions, and the energy
  of the system decreases. (A bond begins to form.) ... At some specific
  distance between the atoms, which varies with the atoms involved, the
  energy reaches its lowest  (most stable) value.  This optimum distance
  between the two bonded nuclei is the bond distance between the two
  atoms.


The text doesn't specify what energy is decreasing, and why.  But I can answer these questions I think.  The energy that is decreasing is the potential energies of the attractive fields of the atoms, and that energy is being transformed to kinetic energy as the atoms accelerate toward each other.

So we have the nuclei accelerating towards each other.  What happens next?

According to the text ... continuing where we left off


  The bond is stable because at this point the attractive and repulsive
  forces combine to create the lowest possible energy configuration.


So there is no mention of the release of energy, and the atoms just arrive at the stable combined state.

Here is what I would expect, given that the nuclei are accelerating towards each other - at some point the repulsive forces become stronger than the attractive forces, and the atoms begin to decelerate.  If there is no damping force on the motion the atoms will oscillate about the point where the attractive and repulsive forces are equal.  So, there must be some damping force on the atoms, that causes them to come rest at the bond distance of H2.

Now comes the mystery, which is, how does the formation of a chemical bond release energy? 

What happens to the kinetic energy of the two nuclei accelerating towards each other?  If the two hydrogen atoms are coming together head on there will be a collision that would appear to cancel out the motion, i.e. kinetic energy, of both atoms.  If there is a damping mechanism that generates the heat, what is it?

Since the energy is released as heat, I think it must be in the form of kinetic or electromagnetic energy, but what is the specific mechanism?

Or, am I trying to get too much out of the kinetic model?
It is easier first to think of what happens when a bond is broken in an exothermic reaction. The energy is initially released into vibrations,  rotations and translational motion of the two fragments. This energy is then lost as these fragments collide with other gas molecules or with solvent molecules and so eventually ends up as heat. 

In exothermic bond formation the extra energy vibrationally and rotationally excites the new molecule and this is then lost via collisions with surrounding gas or solvent molecules and again ends up as heat. 

(If the new molecule were isolated in space (so no collisions) it would remain 'hot' until the energy is radiated away from vibrational levels and until it (radiatively) comes into equilibrium with the surroundings. This is a  slow process, by many orders of magnitude,  compared to collisions in solution or in a gas at normal atmospheric pressure )

In a very few types of reaction an electronically excited state is produced in the product and then photons radiate (as visible light) some of the energy away. This is called chemiluminescence.