In Arrhenius equation , `K=Ae^(-E_a//RT)` . The A is

Options

A. Activation energy
B. Enthalpy of reaction
C. Free energy of reaction
D. Rate constant of the reaction at infinite temperature

Answer

To answer the question regarding the Arrhenius equation \( K = A e^{-\frac{E_a}{RT}} \), we need to identify what the variable \( A \) represents.

### Step-by-Step Solution:

1. **Understanding the Arrhenius Equation**:
The Arrhenius equation describes how the rate constant \( K \) of a chemical reaction depends on temperature \( T \) and activation energy \( E_a \). The equation is given by:
\[ K = A e^{-\frac{E_a}{RT}} \]
where:
- \( K \) = rate constant
- \( A \) = pre-exponential factor (also known as the Arrhenius factor or frequency factor)
- \( E_a \) = activation energy
- \( R \) = gas constant
- \( T \) = temperature in Kelvin

2. **Identifying \( A \)**:
In the context of the Arrhenius equation, \( A \) is not the activation energy, enthalpy of the reaction, or free energy of the reaction. Instead, it is a constant that provides a measure of the frequency of collisions and the orientation of reactants in a reaction.

3. **Behavior at Infinite Temperature**:
When the temperature \( T \) approaches infinity, the term \( -\frac{E_a}{RT} \) approaches zero, making the exponential term \( e^{0} = 1 \). Thus, at infinite temperature:
\[ K = A \cdot 1 = A \]
This implies that \( A \) can be considered as the rate constant \( K \) at infinite temperature.

4. **Conclusion**:
Therefore, in the Arrhenius equation, \( A \) is known as the **pre-exponential factor** or **frequency factor**, and it can also be interpreted as the rate constant at infinite temperature.

### Final Answer:
In the Arrhenius equation, \( A \) is the **pre-exponential factor** or **frequency factor**, which can also be interpreted as the rate constant at infinite temperature.