Answer:
The colliding molecules need to possess certain energy which is greater than the activation energy Ea and proper orientation.
Not all collisions result in a chemical reaction because not all collisions have the have sufficient amount of energy or have the appropriate activation energy. Nor do they all have this correct orientation. Molecules need to collide in such a way that they're oriented, so the correct bonds could break in. The correct bonds conform. And then, of course, they need to have sufficient activation energy in order to initiate the breaking of the bonds.
Hope this helps please let me know If I'm wrong.