For an endothermic reaction, energy of activation is `E_a` and enthalpy of reaction is `DeltaH` (both of these in kJ/mol). Minimum value of E will be

Options

A. Less than `DeltaH`
B. Equal to `DeltaH`
C. More than `DeltaH`
D. Equal to zero

Answer

To determine the minimum value of the activation energy \(E_a\) for an endothermic reaction in relation to the enthalpy change \(\Delta H\), we can follow these steps:

### Step-by-Step Solution

1. **Understand Endothermic Reactions**:
- In endothermic reactions, the enthalpy change \(\Delta H\) is positive. This means that the system absorbs heat from the surroundings.

2. **Draw the Energy Profile Diagram**:
- Create an energy vs. reaction coordinate graph.
- On the y-axis, represent the energy, and on the x-axis, represent the reaction coordinate.
- Mark the energy level of the reactants, the activated complex (transition state), and the products.

3. **Identify Key Energies**:
- Let’s denote the energy of the reactants as \(E_{reactants}\) and the energy of the products as \(E_{products}\).
- The difference in energy between the reactants and products gives us \(\Delta H\):
\[ \Delta H = E_{products} - E_{reactants} \]
- Since \(\Delta H\) is positive for endothermic reactions, \(E_{products} > E_{reactants}\).

4. **Determine Activation Energy \(E_a\)**:
- The activation energy \(E_a\) is the energy difference between the reactants and the activated complex:
\[ E_a = E_{activated\ complex} - E_{reactants} \]
- For an endothermic reaction, the activated complex is at a higher energy level than both the reactants and the products.

5. **Compare \(E_a\) and \(\Delta H\)**:
- Since the activated complex is at a higher energy than the products, we can conclude that:
\[ E_a > \Delta H \]
- Therefore, the minimum value of \(E_a\) must be greater than \(\Delta H\).

### Conclusion
The minimum value of the activation energy \(E_a\) for an endothermic reaction is **greater than \(\Delta H\)**.