Question

Which of the following represents heterogeneous catalytic reaction?

• A. Reduction of iron ore
• B. Ammonia synthesis
• C. Burning of coal
• D. Roasting of ores

Hint:

A heterogeneous catalytic reaction involves a catalyst in a different phase (usually solid) from the reactants (usually gases or liquids), like ammonia synthesis on an iron catalyst.

Answer 1

The Correct Option is B

Step 1: Define a heterogeneous catalytic reaction. 
A heterogeneous catalytic reaction involves a catalyst that is in a different phase from the reactants. Typically, the catalyst is a solid, and the reactants are gases or liquids. The reaction occurs at the surface of the catalyst, where reactants adsorb, react, and desorb as products. Examples include reactions in industrial processes where a solid catalyst facilitates a gas-phase reaction. 
Step 2: Analyze each option. 
Reduction of iron ore: This process (e.g., in a blast furnace) involves reducing iron oxides (e.g., \( Fe_2O_3 \)) to iron using carbon monoxide or hydrogen: \( Fe_2O_3 + 3CO \to 2Fe + 3CO_2 \). While it is a heterogeneous reaction (solid iron ore, gaseous CO), it is not typically catalytic because the carbon (in the form of coke) is consumed as a reactant, not reused as a catalyst.
Ammonia synthesis: The Haber-Bosch process (\( N_2 + 3H_2 \to 2NH_3 \)) is a classic example of a heterogeneous catalytic reaction. Nitrogen and hydrogen (gases) react on the surface of a solid iron catalyst (promoted with oxides like \( K_2O \) or \( Al_2O_3 \)). The catalyst is in a different phase from the reactants, making this a heterogeneous catalytic reaction.
Burning of coal: This is a combustion reaction (\( C + O_2 \to CO_2 \)) where coal (solid) reacts with oxygen (gas). It is a heterogeneous reaction, but it is not catalytic because no catalyst is involved; the reaction consumes the coal.
Roasting of ores: Roasting (e.g., \( 2ZnS + 3O_2 \to 2ZnO + 2SO_2 \)) involves heating sulfide ores in the presence of oxygen to convert them to oxides. This is a heterogeneous reaction (solid ore, gaseous oxygen), but it is not catalytic as no catalyst is used; the reaction is a direct chemical transformation.
Step 3: Evaluate the options. 
(1) Reduction of iron ore: Incorrect, as it is not catalytic; the carbon is a reactant, not a catalyst. Incorrect.
(2) Ammonia synthesis: Correct, as it is a heterogeneous catalytic reaction with a solid iron catalyst and gaseous reactants. Correct.
(3) Burning of coal: Incorrect, as it is a non-catalytic combustion reaction. Incorrect.
(4) Roasting of ores: Incorrect, as it is a non-catalytic process. Incorrect.
Step 4: Select the correct answer. 
Ammonia synthesis represents a heterogeneous catalytic reaction, matching option (2).