Hydrogen peroxide decomposes to form water and oxygen. The uncatalysed reaction has activation energy of 86 kJ/mol. The activation energy value in the presence of acetanilide is 112 kJ/mol and in the presence of MnO₂ it is 49 kJ/mol. What conclusion can you draw from the above observation ?

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Solution

The uncatalysed decomposition of Hydrogen peroxide $(H_{2} O_{2})$ is given by the reaction:
$2 H_{2} O_{2} (l) \to 2 H_{2} O (l) + O_{2} (g)$
The activation energy of a reaction is the minimum amount of energy required by compounds to undergo a chemical reaction.
The activation of uncatalysed decomposition of Hydrogen peroxide is 86 kJ/mol which means it requires a minimum of 86 kJ/mol of energy to decompose into water $(H_{2} O)$ and oxygen gas $(O_{2})$ .
In the presence of catalyst ${MnO}_{2}$ , the activation energy of the same reaction decreases to 49 kJ/mol. It means in less amount of energy Hydrogen peroxide start decomposing and the rate of decomposition of $H_{2} O_{2}$ is increased. Hence, ${MnO}_{2}$ is a positive catalyst.
In the presence of catalyst acetanilide, the activation energy is 112 kJ/mol that is much greater than that of uncatalysed reaction. It means the rate of decomposition of $H_{2} O_{2}$ is decreased in the presence of acetanilide. Hence, acetanilide is a negative catalyst.

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Hydrogen peroxide decomposes into water and oxygen. The uncatalyzed reaction has activation energy of $86 kJ / mol$ . The $E_{a}$ value in the presence of acetanilide is $112 kJ / mol$ and in the presence of ${MnO}_{2}$ it is $49 kJ / mol$ . What conclusion can you draw from the above observations?

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