Q.a) What is effective collision? Write any two factors responsible for effective collision.

Collision theory says a reaction happens only when molecules collide with both enough energy and the right orientation; and for a first-order reaction, working the integrated rate law down to half the initial concentration leaves an expression containing only k. …

a) Effective collision

According to collision theory, molecules must collide to react, but not every collision leads to products. An effective collision is a collision that results in the formation of product molecules.

Two factors (conditions) responsible for an effective collision:

1. Energy factor — the colliding molecules must possess energy equal to or greater than the threshold (activation) energy.
2. Orientation factor — the molecules must collide with the proper orientation so that bonds can break and form.

b) Half-life of a first-order reaction

The integrated first-order rate law is:

At the half-life $t = t_{1/2}$, the concentration falls to half: $[R] = \dfrac{[R]_0}{2}$. Substituting:

$t_{1/2} = \frac{2.303\times0.3010}{k} = \frac{0.693}{k}$ …