An increse in the concentration of the reactants of a reaction leads to change in:

Options

A. activation energy
B. heat of reaction
C. threshold energy
D. collision frequency

Answer

To solve the question "An increase in the concentration of the reactants of a reaction leads to change in:", we will analyze the effects of reactant concentration on various factors in a chemical reaction.

### Step-by-Step Solution:

1. **Understanding Reactant Concentration**:
- The concentration of reactants refers to the amount of reactant present in a given volume. Increasing this concentration means there are more reactant molecules available for the reaction.

2. **Effect on Collision Frequency**:
- When the concentration of reactants increases, the number of molecules in a given volume increases. This leads to a higher likelihood of collisions between reactant molecules.
- Collision frequency is defined as the number of collisions that occur per unit time. With more molecules present, the frequency of collisions increases.

3. **Impact on Reaction Rate**:
- According to collision theory, the rate of a reaction is proportional to the frequency of effective collisions between reactant molecules. Therefore, an increase in collision frequency due to higher reactant concentration will generally lead to an increase in the reaction rate.

4. **Exclusion of Other Factors**:
- **Activation Energy**: This is the minimum energy required for a reaction to occur and does not change with concentration. Thus, it is not affected by the increase in reactant concentration.
- **Heat of Reaction**: This refers to the overall energy change during the reaction and is primarily dependent on the nature of the reactants and products, not their concentrations.
- **Threshold Energy**: Similar to activation energy, this is related to the energy required for reactants to collide effectively and does not depend on concentration.

5. **Conclusion**:
- The primary change that occurs with an increase in the concentration of reactants is an increase in collision frequency. Therefore, the correct answer to the question is that an increase in the concentration of reactants leads to a change in collision frequency.

### Final Answer:
An increase in the concentration of the reactants of a reaction leads to a change in **collision frequency**.