Question

How can I calculate the activation energy of a reaction?

Answer 1

Hint: We know that activation energy of a reaction is the minimum amount of energy that is needed by the reactants to result in products. There is an equation namely Arrhenius equation that proves the temperature dependence of the rate of a chemical reaction.

Complete step by step answer:
Let's discuss the Arrhenius equation in detail. This equation was proposed by a Dutch scientist J.H. van’t Hoff but Swedish chemist, Arrhenius proved this equation. The Arrhenius equation is,
$k = A{e^{ - Ea/RT}}$
Where, k is rate constant, A is Arrhenius factor, ${E_a}$ is the activation energy, R is gas constant and T is temperature. The unit of activation energy is joules/mole.
If we know the value of temperature (T), A and k, we can easily calculate the activation energy of the reaction using the Arrhenius equation.

Additional Information:
Activation energy is given by the energy difference between activated complex and the reactants and A which corresponds to the collision frequency. The Arrhenius equation shows that lowering of Ea or increase of temperature results in an increase in the rate of the reaction and in presence of a catalyst the activation energy is lowered because the catalyst provides an alternate path for the reaction. The collision theory provides another factor P (Steric factor) that refers to the orientation of the molecules which undergo collision and contributes to effective collisions.


Note: It is to be noted that there are many factors on which activation energy depends such as nature of reactants and effect of catalyst. The presence of a positive catalyst speeds up the reaction. But the activation energy does not depend on pressure, temperature, volume and concentration of reactants.