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For an endothermic reaction, energy of activation is $E_a$ and enthalpy of reaction is $\Delta H$ (both of these in kJ/mol). Minimum value of $E_a$ will be
A
Equal to zero
B
Less than $\Delta H$
C
Equal to $\Delta H$
D
More than $\Delta H$
Detailed Solution
In an endothermic reaction the products lie at a higher energy than the reactants by $\Delta H$.
The reactants must climb to the top of the energy barrier (the activated complex), which lies above the products.
From the energy profile: $E_a(\text{forward}) = \Delta H + E_a(\text{backward})$
$E_a(\text{backward})$ is always a positive quantity.
Therefore $E_a(\text{forward}) > \Delta H$; the activation energy must be more than $\Delta H$.
The reactants must climb to the top of the energy barrier (the activated complex), which lies above the products.
From the energy profile: $E_a(\text{forward}) = \Delta H + E_a(\text{backward})$
$E_a(\text{backward})$ is always a positive quantity.
Therefore $E_a(\text{forward}) > \Delta H$; the activation energy must be more than $\Delta H$.