Question

Hydrogen peroxide decomposes into water and oxygen. The uncatalyzed reaction has activation energy of $86\mathrm{kJ}/\mathrm{mol}$. The ${\mathrm{E}}_{\mathrm{a}}$ value in the presence of acetanilide is $112\mathrm{kJ}/\mathrm{mol}$ and in the presence of ${\mathrm{MnO}}_2$ it is $49\mathrm{kJ}/\mathrm{mol}$. What conclusion can you draw from the above observations?

Answer 1

1. Catalyst: A substance that increases the rate of a reaction without itself undergoing any permanent change chemically or quantitatively is called a catalyst. It does so by decreasing the activation energy or proceeding through an alternative path for reaction.
2. Activation energy: The minimum energy in excess of their normal energy that the molecules must acquire so as to react in collision with each other is known as the activation energy.
3. The given reaction is: $$\begin{gathered} 2{\mathrm{H}}_2{\mathrm{O}}_2\left(\mathrm{l}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \\ \mathrm{Hydrogen}\mathrm{Water}\mathrm{Oxygen} \\ \mathrm{peroxide} \end{gathered}$$
4. This reaction is carried in the presence of either acetanilide (${\mathrm{E}}_{\mathrm{a}}=112\mathrm{kJ}/\mathrm{mol}$) or Manganese oxide (${\mathrm{MnO}}_2$) with ${\mathrm{E}}_{\mathrm{a}}=49\mathrm{kJ}/\mathrm{mol}$.
5. Now, lower activation energy means the reaction will proceed faster.
6. Conclusion: As the activation energy of the reaction in presence of Manganese oxide (${\mathrm{MnO}}_2$) is lesser than in presence of acetanilide, thus the given reaction will proceed faster in presence of Manganese oxide (${\mathrm{MnO}}_2$).