Problem 23 - Chemistry Class 9

Question

The addition of \(\mathrm{MnO}_{2}\) to \(\mathrm{KClO}_{3}\) decreases the temperature at which \(\mathrm{KClO}_{3}\) decomposes because \(\mathrm{MnO}_{2}\) added acts as a ____ catalyst.

Step-by-Step Solution

Answer

The addition of MnO2 to KClO3 decreases the temperature at which KClO3 decomposes because MnO2 added acts as a homogeneous catalyst.

Step 1: Recall the types of catalysts

There are two main types of catalysts: homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts function in the same phase as the reactants, while heterogeneous catalysts function in a different phase.

Step 2: Determine the phases of MnO2 and KClO3

Manganese dioxide (MnO2) is a solid and potassium chlorate (KClO3) is also a solid at room temperature. When KClO3 is heated and decomposes, MnO2 is still in solid form. Therefore, both the catalyst (MnO2) and the reactants (KClO3) are in the same phase (solid).

Step 3: Identify the type of catalyst MnO2 acts as in the reaction with KClO3

Since both MnO2 and KClO3 are in the same phase during the reaction and MnO2 acts as a catalyst, MnO2 is a homogeneous catalyst in this case.

Step 4: Complete the sentence

The addition of \(\mathrm{MnO}_{2}\) to \(\mathrm{KClO}_{3}\) decreases the temperature at which \(\mathrm{KClO}_{3}\) decomposes because \(\mathrm{MnO}_{2}\) added acts as a homogeneous catalyst.

Key Concepts

Homogeneous Catalysts

Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. When both the catalyst and reactants reside in the same phase, such as solids, liquids, or gases, the catalyst is deemed homogeneous. These catalysts provide an environment that stabilizes reactive intermediates, thereby reducing the energy required for reactions to proceed. In many cases, they offer the advantage of uniform distribution within the reaction mixture, leading to potentially more efficient reactions.
This is particularly useful in reactions involving gases or liquids, where the catalyst needs to mix well to facilitate the reaction. However, homogeneous catalysts can sometimes be more challenging to recover and reuse from the reaction mixture than heterogeneous catalysts. Their application in chemistry is diverse, ranging from industrial to biochemical processes.

Heterogeneous Catalysts

Unlike homogeneous catalysts, heterogeneous catalysts exist in a different phase than the reactants. Commonly, these are solid catalysts interacting with liquid or gaseous reactants. This type of catalysis involves surfaces where reaction intermediates are formed, facilitating the reaction by providing different pathways.
The catalytic process usually takes place on the surface of the solid catalyst, which allows the catalyst to be easily separated from the products. This property is particularly valuable in industrial processes, like the synthesis of ammonia and the refinery of petroleum.

• Solid-gas reactions like the Haber process use solid iron catalysts.
• Solid-liquid reactions sometimes involve metal catalysts like platinum in hydrogenation reactions.

This difference from homogeneous catalysts illustrates the versatility of catalytic processes in various fields.

Chemical Decomposition

Chemical decomposition is a type of chemical reaction where a single compound breaks down into two or more elements or new compounds. It often requires an input of energy in the form of heat, light, or electricity. This process is crucial in many industrial applications and natural occurrences, such as the decomposition of water into hydrogen and oxygen or the breakdown of organic matter.
In laboratory experiments, decomposition reactions can be critical for understanding the composition and stability of certain compounds. In the example provided, potassium chlorate ( KClO_3) decomposes upon heating with manganese dioxide, indicating decomposition reactions can also be influenced significantly by catalysts.

Manganese Dioxide

Manganese dioxide ( MnO_2) is a chemical compound frequently used as a catalyst in decomposition reactions due to its stability and effectiveness in lowering the activation energy required for reactions. It appears often as a black or brown solid, and is notable for its role in accelerating reactions without itself changing chemically.
In the decomposition of potassium chlorate ( KClO_3), manganese dioxide acts as a catalyst that helps lower the temperature necessary for the decomposition to occur. This characteristic makes it invaluable in chemical processes where controlling temperature is crucial, such as synthesis and breakdown reactions.

Temperature Effect on Reactions

Temperature plays a significant role in the rate and occurrence of chemical reactions. Generally, increasing the temperature increases the energy of molecules, thus increasing reaction rates by providing more particles the energy needed to surpass the activation energy barrier. Conversely, lowering the temperature can slow down the reaction.
In catalyzed reactions, the presence of a catalyst can compensate for lower temperatures by providing alternative pathways with lower activation energies. This is why adding manganese dioxide to potassium chlorate allows it to decompose at a lower temperature than it would otherwise. Understanding how temperature and catalysts interact to impact reaction rates is fundamental in both academic settings and industrial applications.