explain equilibrium in terms of the collision theory

Answer 1

It depends on the reaction or change you want to describe.

In many reactions, if reactants collide with sufficient incoming energy, they form a new compound, with a relase of energy (it, the new particle is vibrating, rotating, or translating). The reverse reaction if somehow energy is released, through a collision, or other, the compound breaks up into reactants. Both of these reactions, forward, and reverse, depend on temperature, pressure...so eqilibrium is when both reactions have the same rate.