Collision theory postulates are:

A. Reactant molecules collide with each other.
B. The collisions must be of sufficient kinetic energy.
C. The collision in molecules with proper orientation.
D. Rate of reaction does not depend on temperature.

Choose the correct answer from the options given below:

A, B and C only

The correct answer is Option (1) → A, B and C only.

Let us break down each aspect of collision theory in detail, explaining its significance and how it applies to chemical reactions.

Collision Theory Overview

Collision Theory is a theoretical framework used to understand the rates of chemical reactions. It posits that reactions occur when reactant molecules collide with sufficient energy and proper orientation. Here’s a detailed exploration of its key components:

Key Postulates of Collision Theory

Reactant Molecules Collide:

The first postulate states that for a reaction to occur, the reactant molecules must collide with each other. Each collision can potentially lead to a reaction if conditions are right.

The frequency of these collisions directly influences the reaction rate. More collisions lead to more opportunities for the reactants to interact and convert into products.

In a gas-phase reaction, increasing the concentration of reactant gases increases the number of molecules in a given volume, resulting in more frequent collisions.

The Collisions Must Be of Sufficient Kinetic Energy:

Not all collisions are effective in producing a reaction. For a collision to lead to a reaction, the colliding molecules must possess enough kinetic energy to overcome the activation energy barrier. This energy is necessary to break bonds in the reactants and form new bonds in the products.

The concept of activation energy is critical; if the collision energy is less than the activation energy, the reactants will not react even if they collide.

For instance, when heating a reaction mixture, molecules gain kinetic energy, leading to more energetic collisions and an increased reaction rate.

The Collision Must Occur with Proper Orientation:

Even if the molecules collide with sufficient energy, they may not react unless they are oriented correctly during the collision. The correct orientation allows the reactive parts of the molecules to interact effectively, facilitating the breaking and forming of bonds.

This requirement explains why some reactions occur at slower rates despite having sufficient energy; improper orientation during collisions can prevent reactions from taking place.

In reactions involving large or complex molecules, the probability of achieving the correct orientation is lower, which can lead to slower reaction rates.

Rate of Reaction Depends on Temperature:

Temperature plays a crucial role in the kinetic energy of molecules. As the temperature increases, the average kinetic energy of the molecules also increases, leading to more frequent and energetic collisions. This typically results in an increased rate of reaction.

This explains why many reactions proceed faster at higher temperatures. Moreover, the Arrhenius equation quantitatively describes how temperature affects the rate constant of a reaction.

Consider a reaction that occurs at both 25 °C and 50 °C. At the higher temperature, more molecules have enough energy to overcome the activation energy barrier, increasing the reaction rate significantly.

Evaluating the Given Statements

Now, let us evaluate each of the provided statements about collision theory:

A. Reactant molecules collide with each other.

True: This is the fundamental premise of collision theory. Without collisions, no reaction can occur

B. The collisions must be of sufficient kinetic energy.

True: This is essential for reactions to take place. The energy of the colliding molecules must be greater than or equal to the activation energy.

C. The collision in molecules with proper orientation.

True: The effectiveness of a collision depends not only on energy but also on the correct spatial arrangement of the molecules involved.

D. Rate of reaction does not depend on temperature.

False: This statement is incorrect. The rate of reaction is significantly influenced by temperature, with higher temperatures generally leading to increased reaction rates due to more frequent and effective collisions.

Conclusion

Given this detailed breakdown, we conclude that the correct answer, based on the valid postulates of collision theory, is: A, B, and C only.