Question

The heat evolved during chemisorption lies in the range of _____.

• A. $20\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $40\mathrm{kJ}{\mathrm{mol}}^{-1}$
• B. $40\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $80\mathrm{kJ}{\mathrm{mol}}^{-1}$
• C. $80\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $240\mathrm{kJ}{\mathrm{mol}}^{-1}$
• D. $20\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $100\mathrm{kJ}{\mathrm{mol}}^{-1}$

Answer 1

The correct option is C

$80\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $240\mathrm{kJ}{\mathrm{mol}}^{-1}$

The explanation for the correct answer
Option (C) $80\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $240\mathrm{kJ}{\mathrm{mol}}^{-1}$

• The heat evolved during chemisorption lies in the range of 80 kJ/mol to 240 kJ/mol.
• In chemisorption, the molecules are adsorbed by a solid substance.
• The type of bond formed in chemisorption is a chemical bond.
• The chemical bond is strong in nature.
• During the formation of the chemical bond, heat is evolved.
• As the type of the bond is chemical and heat is evolved, then the reaction is highly exothermic.
• For a highly exothermic reaction, the numerical value must be high.
• From all the options given above, 80 kJ/mol to 240 kJ/mol has the highest numerical value.

The explanation for the incorrect answer

Option (A) $20\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $40\mathrm{kJ}{\mathrm{mol}}^{-1}$

• In chemisorption, there is the formation of the chemical bond.
• During the formation of the chemical bond, heat is evolved.
• As the type of the bond is chemical and heat is evolved, then the reaction is highly exothermic.
• The numerical value, 20 kJ/mol to 40 kJ/mol is much lower for an exothermic reaction to happen.

Option (B) $40\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $80\mathrm{kJ}{\mathrm{mol}}^{-1}$

• In chemisorption, there is the formation of the chemical bond.
• During the formation of the chemical bond, heat is evolved.
• As the type of the bond is chemical and heat is evolved, then the reaction is highly exothermic.
• The numerical value, 40 kJ/mol to 80 kJ/mol is much lower for an exothermic reaction to happen.

Option (D) $20\mathrm{kJ}{\mathrm{mol}}^{-1}$ to $100\mathrm{kJ}{\mathrm{mol}}^{-1}$

• In chemisorption, there is the formation of the chemical bond.
• During the formation of the chemical bond, heat is evolved.
• As the type of the bond is chemical and heat is evolved, then the reaction is highly exothermic.
• The numerical value, 20 kJ/mol to 100 kJ/mol is much lower for an exothermic reaction to happen.

Hence due to the high numerical value, the heat evolved during chemisorption lies in the range of 80 kJ/mol to 240 kJ/mol, option (C) is correct.