8.1.2—

For a collision to produce products, particles must collide with energy at least equal to the activation energy and with an orientation that allows bonds to rearrange.

Many collisions are unsuccessful. Changing conditions can alter the fraction that is energetic enough or the number of collisions per second.

Heating a reacting mixture increases the fraction of particles with energy above Eₐ, so more collisions become successful even though the activation-energy threshold itself is unchanged.

Particles do not all have the same kinetic energy, and simply colliding is not enough. Both energy and orientation matter.