Question

Which requires a catalyst
A. $S+O_{2} \rightarrow SO_{2}$
B. $2SO_{2}+O_{2} \rightarrow2SO_{3}$
C. $C+O_{2} \rightarrow CO_{2}$
D. All

Answer 1

Hint: Catalyst is a substance that improves the rate at which a reactant reacts and doesn't get used up in the process. This process is called catalysis.

Complete Step by Step Answer:
- The reaction happens at a faster rate after the addition of a catalyst.
- The catalyst does not possess any change in terms of the chemical composition and mass after the end of the reaction.
- It does not get destroyed during the reaction.
- It reduces the activation energy of the reactants. Due to lower activation energy, a significant number of reactant species partake in the reaction thereby raising the rate of reaction.
- Its physical state like size, colour, etc., may alter.
- When in a reaction the catalyst is present in the identical phase as the reactants, it is called homogeneous catalysis.
For example,
Gaseous phase:
In this type of reaction, the reactant, and catalyst are from the gaseous phase.
A) Reaction of sulphur dioxide and oxygen in presence of nitric acid.
B) Decomposition of acetaldehyde in the presence of iodine vapours.
Liquid phase:
The reactant and catalyst both are in the liquid phase.
A) Hydrolysis of cane sugar in presence of a mineral acid.
B) Hydrolysis of the ester
So, B is correct.
So, option D is correct.

Note: We know that sulphuric acid is vastly important in the chemicals industry.
It is yielded by the Contact Process and involves three steps. The first step is the burning of sulphur or sulphide ores in the air to generate sulphur dioxide. The second step is the conversion of sulphur dioxide to sulphur trioxide by the reaction of sulphur dioxide with oxygen in the presence of a catalyst vanadium peroxide. The last step is the absorption of sulphur trioxide in sulphuric acid to provide Oleum.