NEET 2020 Chemistry Question 109 Solution

According to collision theory, the collision frequency ($$Z$$) is defined as the number of collisions per second per unit volume of the reacting mixture. For a bimolecular reaction $$A + B \to \text{Products}$$, the collision frequency is directly proportional to the product of molar concentrations: $$Z_{AB} \propto [A][B]$$.

When the concentration of reactants is increased, the number of reactant particles per unit volume increases. As a consequence, molecules collide more frequently with each other, leading to a direct increase in the collision frequency ($$Z$$).

Activation energy ($$E_a$$) is the minimum extra energy required by reactant molecules to reach the activated transition state. It is an intrinsic feature of the reaction mechanism and is completely independent of reactant concentration (changed only by a catalyst).

Heat of reaction ($$\Delta_r H$$) is the difference in enthalpy between products and reactants per mole. It is a thermodynamic property determined by chemical bond energies, not affected by initial concentration.