these all collisions between molecules of reactiong substances result in a chemical union?

Not all collisions between molecules can lead to the occurrence of chemical reactions.

Reaction occurs only when the collisions between molecules fulfill the following three conditions:
(1) The reaction is possible.
(2) The molecules collides in a suitable orientation.
(3) The collision energy is higher than the activation energy.

most collisions do not result in remaking of bonds or creation of bonds between the colliding atoms or molecules. Must have just the correct energy and orientation.

No