Question

Which of the following easily catalyse the decomposition of \(\mathrm{H}_{2} \mathrm{O}_{2}\) when stored? (i) Rough surface (ii) Sunlight (iii) Dust particles (iv) Metals (a) (i) and (ii) (b) (i), (ii) and (iii) (c) (ii) and (iii) (d) All of these.

Short answer

All of the given factors, including rough surfaces, sunlight, dust particles, and metals, can catalyze the decomposition of \(\mathrm{H}_{2}\mathrm{O}_{2}\), which means the correct answer is (d) All of these.

Step-by-step solution

Understanding the Decomposition of Hydrogen Peroxide

Hydrogen peroxide \(\mathrm{H}_{2}\mathrm{O}_{2}\) is known to decompose into water and oxygen over time. This decomposition can be accelerated by various factors. Each option provided needs to be assessed on its capability to catalyze the decomposition.

Assessing Rough Surface

A rough surface can increase the rate of decomposition of hydrogen peroxide as it provides a larger surface area for the reaction to take place. Thus, a rough surface acts as a catalyst.

Assessing Sunlight

Sunlight can provide the energy necessary to break the bonds of the hydrogen peroxide molecules, speeding up the decomposition process. Hence, sunlight can also act as a catalyst.

Assessing Dust Particles

Dust particles can contain various substances including metals that can serve as a surface for the decomposition reaction or can provide the necessary energy by absorbing and releasing heat or light. As a result, dust particles are potential catalysts.

Assessing Metals

Certain metals like manganese dioxide are well-known catalysts that drastically increase the decomposition rate of hydrogen peroxide. Metals generally provide a surface for the reaction to occur more efficiently.

Conclusion

Considering all the factors above, it is clear that all the options listed (i) Rough surface, (ii) Sunlight, (iii) Dust particles, and (iv) Metals have the potential to catalyze the decomposition of hydrogen peroxide. Therefore, option (d) is correct.

Key concepts

Catalysis

Catalysis is a process where the rate of a chemical reaction is increased by a substance called a catalyst. A catalyst provides an alternative pathway for the reaction with lower activation energy. It does this without being consumed in the reaction itself, allowing for the repeated acceleration of the process. In the decomposition of hydrogen peroxide, any agent that can speed up the reaction by lowering the activation energy or providing a surface for the reaction to take place more readily is a catalyst. This includes a rough surface, sunlight, dust particles, and certain metals.

Surface Area Effect on Reaction Rate

The surface area of reactants is a significant factor in the rate of a chemical reaction. A larger surface area allows more reactant particles to be exposed and available for reaction at any given time. In the context of catalysis, a rough surface typifies an increased surface area. Consequently, when the surface area is boosted, for instance, by creating a rough texture, the number of available active sites for the chemical reaction to occur is enhanced. This amplifies the decomposition rate of hydrogen peroxide as there are more opportunities for the reactant molecules to interact with the surface of the catalyst.

Photochemical Reactions

Photochemical reactions involve the absorption of light, usually sunlight, to facilitate chemical reactions. Sunlight is composed of photons, which can provide the necessary energy to break chemical bonds. In the case of hydrogen peroxide, sunlight can supply the energy to break the O-O bond, leading to the formation of water and oxygen gas. This reaction pathway induced by sunlight is a form of photochemical catalysis. It illustrates how light energy can be harnessed to accelerate chemical reactions without the need for additional heat or chemical reagents.

Role of Metals in Catalysis

Metals often play a crucial role in catalysis due to their unique electronic properties and ability to provide reactive surfaces. Certain metals, when added to hydrogen peroxide, can facilitate the decomposition by providing a platform where the reactive molecules of H₂O₂ can interact with metal atoms. These interactions can help lower the activation energy, making it easier for hydrogen peroxide molecules to decompose into water and oxygen. Metals like manganese dioxide are especially effective, making them common choices for catalyzing the decomposition of hydrogen peroxide and widely used in industrial and laboratory settings.