Ncert Exercises & Solutions

The correct statements among the following about solid catalysts is -

a.	Same reactants may give different products by using different catalysts
b.	Catalyst does not change ∆ H of reaction
c.	Catalyst is required in large quantities to catalyse reactions
d.	Catalytic activity of a solid catalyst does not depend upon the strength of chemisorption

1. a and b
2. b and c
3. c and d
4. a and d

Hint: Catalyst does not change ∆ H of reaction

(a) Same reactants may give different products by using different catalysts as different catalysis have different selectivity functions to mold the reaction towards selective product. e.g., starting with H₂ and CO₂ and using different catalysts, we get different products.

(i) C O (g) + 3 H_{2} \overset{N i}{\to} C H_{4} (g) + H_{2} O (g)

(i i) C O (g) + 2 H_{2} (g) \to_{C r_{2} O_{3}}^{C u / Z n O} C H_{2} O H (g)

(i i i) C O (g) + H_{2} (g) \overset{C u}{\to} H C l I O (g)

(b) Catalyst does not change

∆ H

of reaction as

∆ H

of reaction is difference between enthalpy of reactants and products. So, it not change during catalysed reaction.

(c) Catalyst is required in large quantities to catalyse reactions is wrong statement, catalyst amount for a reaction is very small.

(d) Catalytic activity of a solid catalyst does not depend upon the strength of chemisorption, is wrong statement. It depends on the strength of chemisorption.

Hence, option one is the correct answer.

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