Question

Which reactions represent heterogeneous catalysis?
A.Decomposition of $Kl{O_3}$ in presence of $Mn{O_2}$
B.Ostwald process of $HN{O_3}$
C.Contact process for ${H_2}S{O_4}$
D.Acidic hydrolysis of ester.

Answer 1

Basically, in heterogeneous catalysis, the reacting substances in a reaction and catalyst employed in that reaction are not in the same state of matter. Further, it involves both adsorption as well as intermediate compound formation.

Complete step by step answer:
Catalysts are defined as those substances which alter the rate of a reaction by changing the path of the reaction. In most of the cases, a catalyst is used to speed up or increase the rate of the reaction. We can also say that catalysts encourage molecules to react and make the whole reaction process easier and efficient. Now, when a catalyst is used to increase the rate of a chemical reaction, then this phenomenon is known as catalysis.
Further, on the basis of nature and the physical state of substance employed in the chemical reaction, there are three types of catalysis.
1.Homogeneous catalysis
2.Heterogeneous catalysis
3.Autocatalysis
Now, we will discuss the types of catalysis. The first one is heterogeneous catalysis. In this type, the reacting substances in a reaction and catalyst employed in that reaction are not in the same state of matter. For example, preparation of ammonia by Haber’s process, Manufacture of sulfuric acid by contact process, Ostwald process of $HN{O_3}$ , Decomposition of $KCl{O_3}$ in presence of $Mn{O_2}$ etc. the phase in this type of catalysis not only refers to solid, liquid or gas but also to immiscible liquids.
The next one is homogeneous catalysis. In this type of catalysis, the catalyst employed in the reaction and the reactants are in the same state of matter. For example, hydrolysis of ethyl acetate in the presence of dilute acid, oxidation of Sulphur dioxide in the lead chamber process etc. Some of the equations of these reactions are as shown:
$C{H_3}COO{C_2}{H_5} + {H_2}OCl \to C{H_3}COOHCl + {C_2}{H_5}OHCl$

$2S{O_2} + {O_2}\xrightarrow{{NO}}2S{O_3}$
The last one is autocatalysis. In this type, there is no specific catalyst that is added. Instead, one of the products acts as a catalyst and increases the rate of formation of products. For example, permanganate vs oxalic acid, during this process, $M{n^{ + 2}}$ that is formed, further acts as an auto catalyst.
So, form the given options, decomposition of $KCl{O_3}$ in presence of $Mn{O_2}$ , Ostwald process for $HN{O_3}$ , and contact process for ${H_2}S{O_4}$ represent heterogeneous catalysis.

Hence, option A, B and C are correct.

Note: There are several types of catalysts such as positive catalyst, negative catalyst, promotors, inhibitors etc. The catalysts that increase the rate of a chemical reaction are known as positive catalysts whereas the catalysts which decrease the rate of reaction are known as negative catalysts.