According to the collision theory of reaction rates, an increase in the temperature at which the reaction occurs will inturn increase the rate of the reaction. This is caused due to:

Greater number of molecules are having the activation energy (threshold energy)

The correct answer is option 1. Greater number of molecules are having the activation energy (threshold energy).

The collision theory of chemical reactions provides a framework to understand how the rate of a reaction depends on various factors such as temperature, concentration, and the nature of reactants. Here’s a detailed explanation of why an increase in temperature increases the rate of reaction according to the collision theory:

Collision Theory Overview

The collision theory proposes that for a chemical reaction to occur, several conditions must be met:

Collision between molecules: Reactant molecules must collide with each other.

Proper orientation: Colliding molecules must have the correct orientation relative to each other.

Activation energy: Colliding molecules must possess kinetic energy equal to or greater than the activation energy (\( E_a \)) required to initiate the reaction.

Effect of Temperature on Reaction Rate

Temperature directly affects reaction rate due to its influence on the kinetic energy of molecules:

Kinetic energy distribution: Temperature represents the average kinetic energy of molecules in a substance. At higher temperatures, more molecules have higher kinetic energies compared to lower temperatures where fewer molecules reach the necessary energy levels.

Activation energy distribution: The activation energy (\( E_a \)) is the minimum energy required for a reaction to occur. At higher temperatures, the distribution of molecular kinetic energies shifts towards higher values. This means that a greater proportion of molecules have energies equal to or greater than the activation energy (\( E_a \)), making successful collisions more likely.

Specifically Addressing the Options:

1. Greater number of molecules are having the activation energy (threshold energy):

This statement is correct. As temperature increases, a larger fraction of molecules in the reaction mixture have kinetic energies equal to or greater than the activation energy (\( E_a \)). Therefore, more collisions occur that result in a successful reaction.

2. Greater velocity of reaction molecules:

Temperature does increase the average velocity of molecules due to increased kinetic energy, but the primary factor affecting reaction rate is the number of molecules with sufficient energy, not just their velocity.

3. Greater number of collisions:

Higher temperature does increase collision frequency because molecules move faster and collide more frequently. However, the key factor is the increase in the number of effective collisions where molecules have sufficient energy to react.

Conclusion: Thus, according to the collision theory, an increase in temperature increases the rate of reaction primarily because a greater number of molecules have kinetic energies equal to or exceeding the activation energy (\( E_a \)). This increases the likelihood of successful collisions that lead to chemical reaction initiation.