Question

What are effective collisions?
(This question has multiple correct options)
(A) collisions leading to the transformation of reactants to products.
(B) formation of activated complex.
(C) collision between two reactants to decrease the activation energy.
(D) collision between two reactants to overcome activation energy barrier.

Answer 1

Hint: The number of collisions that result in product formation are much lower than the total number of collisions. This is because a significant portion of collisions are ineffective collisions.

Complete step by step answer:
When two (or more) reactants collide, they may or may not form products. In other words, during the collision of two (or more) reactant molecules may or may not result in reaction. When two (or more) reactant molecules collide, and the collision results in the formation of the product, then you can say that the collision is an effective collision. When two (or more) reactant molecules collide, and the collision does not result in the formation of the product, then you can say that the collision is NOT an effective collision or it is an ineffective collision.
When two (or more) reactant molecules collide, and if the collision is an effective collision, the activated complex is formed, which then is converted to products.
The following factors determine if the collision is effective or not.
(i) The colliding molecules should have energy equal to or greater than activation energy.
(ii) The colliding molecules should have proper orientation.
If the colliding reactant molecules have energy less than activation energy, then the collision will NOT be an effective collision. This collision will not result in the product formation.
If the colliding reactant molecules have improper orientation, then the collision will NOT be an effective collision. This collision will not result in the product formation.
If the colliding reactant molecules have energy greater than activation energy and proper orientation, then the collision will be an effective collision. This collision will result in the product formation.
Hence, the following are effective collisions:
(A) Collisions leading to the transformation of reactants to products.
(B) formation of activated complex.
(D) collision between two reactants to overcome activation energy barrier.
The collision between two reactants does not change (increase or decrease) the activation energy. Hence, the option (C) is an incorrect option.

Hence, the correct options are the options (A), (B) and (D).

Note: Activation energy is the difference between the energy of the activated complex (the transition state) and the energy of the reactants. Threshold energy is the energy of the activated complex (the transition state).