Question

The activation energy for the reaction NO2 (g )+ CO (g) ⟶ NO (g) + CO2 (g) is Ea = 217 kJ/mol and the change in enthalpy for the reaction is ΔH = -293 kJ/mol .
What is the activation energy for the reverse reaction?

Enter your answer numerically and in terms of kJ/mol.

Answer 1

Answer : The activation energy for the reverse reaction is 510 kJ/mol.

Explanation :

Activation energy : It is defined as the minimum amount of energy given to the reactant so that it gets converted into products.

The relation between the activation energy for forward and backward reaction and change in enthalpy of reaction for exothermic reaction is:

When activation energy for forward reaction is less than the activation energy for backward reaction then the reaction will be exothermic. In exothermic reaction the enthalpy change will be negative.

$Ea^b=Ea^f+|\Delta H|$

The relation between the activation energy for forward and backward reaction and change in enthalpy of reaction for endothermic reaction is:

When activation energy for forward reaction is more than the activation energy for backward reaction then the reaction will be endothermic. In endothermic reaction the enthalpy change will be positive.

$Ea^f=Ea^b+|\Delta H|$

where,

$Ea^f$ = activation energy for forward reaction

$Ea^b$ = activation energy for backward reaction

$\Delta H$ = change in enthalpy of reaction

As per question, the value of enthalpy change is -293 kJ/mol that means the reaction will be exothermic reaction. So,

$Ea^b=Ea^f+|\Delta H|$

Given:

$Ea^f$ = activation energy for forward reaction = 217 kJ/mol

$Ea^b$ = activation energy for backward reaction = ?

$\Delta H$ = change in enthalpy of reaction = -293 kJ/mol

Now put all the given values in above relation, we get:

$Ea^b=217kJ/mol+|-293kJ/mol|$

$Ea^b=217kJ/mol+293kJ/mol$

$Ea^b=510kJ/mol$

Therefore, the activation energy for the reverse reaction is 510 kJ/mol.