\(2KClO_3 \overset{653 - 873 K}{\longrightarrow}2KCl + 3O_2\)

On adding manganese dioxide to the above reaction, the subsequent decomposition  takes place at

Lower temperature

The correct answer is option 1. Lower temperature.

The thermal decomposition of potassium chlorate (\(KClO_3\)) is represented by the following equation:

\(2KClO_3 \overset{653 - 873 \, K}{\longrightarrow} 2KCl + 3O_2\)

In this reaction, potassium chlorate decomposes into potassium chloride (\(KCl\)) and oxygen gas (\(O_2\)) when heated to a temperature between 653 K and 873 K.

Role of Manganese Dioxide (\(MnO_2\)) as a Catalyst:

Catalyst: Manganese dioxide (\(MnO_2\)) is a commonly used catalyst in this reaction. A catalyst is a substance that increases the rate of a chemical reaction without undergoing any permanent chemical change itself.

Function of \(MnO_2\): When \(MnO_2\) is added to the reaction, it provides an alternative pathway for the decomposition of \(KClO_3\) that has a lower activation energy.

Activation Energy and Reaction Rate:

Activation Energy: This is the minimum energy required for a chemical reaction to occur. For potassium chlorate to decompose, the molecules must gain enough energy to break the bonds and form the products (potassium chloride and oxygen).

Lowering Activation Energy: By adding \(MnO_2\), the activation energy is lowered, meaning that the molecules of \(KClO_3\) require less energy to start breaking down. As a result, the reaction can occur at a lower temperature.

Effect of Lower Temperature:

Temperature Dependence: Without a catalyst, the decomposition of \(KClO_3\) requires heating to 653-873 K because this is the temperature range at which sufficient activation energy is provided to the molecules.

With \(MnO_2\): The presence of \(MnO_2\) allows the decomposition to start at a lower temperature, making the reaction more efficient. This is because the catalyst lowers the energy threshold needed for the reaction to proceed.

Importance of Catalysts in Chemical Reactions:

Increased Reaction Rate: Catalysts speed up chemical reactions, making processes more efficient and often allowing reactions to proceed at lower temperatures and pressures.

No Change in Thermodynamics: It's important to note that while catalysts affect the rate of reaction and the activation energy, they do not alter the thermodynamic properties of the reaction, such as the overall energy change (\(\Delta H\)).

Summary:

Without Catalyst: \(KClO_3\) decomposes at 653-873 K

With Catalyst (\(MnO_2\)): The decomposition occurs at a lower temperature because the catalyst lowers the activation energy required for the reaction.

This is why the correct answer is option 1: Lower temperature. The addition of manganese dioxide enables the decomposition of potassium chlorate to occur at a lower temperature than it would in the absence of the catalyst.