Question

How does the collision theory explain reaction times?

Answer 1

To determine the answer to this question we should know what collision theory is. As the name indicates this theory tells the reaction starts by the collisions between the reactant molecules. By the collision, reactant molecules cross the energy barrier to form the product. Reaction time is the time required by the reactant molecules to convert into products molecules. The reaction time depends upon the feasibility of the reaction.

Complete step by step answer:
The collision theory explains us about the rate of reaction means how fast or slow a reaction will be. The collision theory is mainly based upon the collisions between reacting molecules.
According to collision theory, during a chemical reaction, the reactant molecules collide so their energy increases to cross over the energy barrier to form an activated complex and the product.

According to collision theory, the rate of the reaction depends upon three factors:
1. Collision frequency
2. Number of effective collisions
3. Fraction of molecules possessing the energy equal to greater than the activation energy.

So, we can write the rate constant of a reaction according to the collision theory as,
${\text{K}}\,{\text{ = }}\,{\text{PZ}}{{\text{e}}^{{{\text{E}}_{\text{a}}}{\text{/RT}}}}$
Where,
K is the rate constant
Z is the number of effective collision or collision frequency

${{\text{e}}^{{{\text{E}}_{\text{a}}}{\text{/RT}}}}$ is the Fraction of molecules possessing the energy equal to greater than the activation energy. So, the collision theory explains reaction times in terms of effective collision with proper orientations.

Therefore, if the collision frequency, the number of effective collisions with proper orientation are high then the rate of the reaction will be high.

Note: The collision theory considered the molecules as a hard-sphere. The number of collisions per second and unit volume of the reaction medium is known as collision frequency. The energy required to form the activated complex is known as activation energy. All the collisions do not lead to the formation of an activated complex because all collisions do not have sufficient only those collisions in which molecules are in proper orientation lead to the energy of the molecule equal to the greater than the activation energy, cause the formation of the activated complex. These collisions which lead to the formation of the product are known as effective collisions and defined in terms of probability factor or steric factor.