To determine whether the given reaction is endothermic or exothermic by analyzing the bond energy, we need to calculate the total bond energy of the bonds broken in the reactants and the total bond energy of the bonds formed in the products.
Step 1: Calculate the total bond energy of the reactants.
In the reactants, we have:
- 4 H–C bonds: \( 4 \times 411 , \text{kJ/mol} = 1644 , \text{kJ/mol} \)
- 4 Cl–Cl bonds: \( 4 \times 242 , \text{kJ/mol} = 968 , \text{kJ/mol} \)
Total bond energy of reactants: \[ 1644 , \text{kJ/mol} + 968 , \text{kJ/mol} = 2612 , \text{kJ/mol} \]
Step 2: Calculate the total bond energy of the products.
In the products, we have:
- 4 C–Cl bonds: \( 4 \times 327 , \text{kJ/mol} = 1308 , \text{kJ/mol} \)
- 4 H–Cl bonds: \( 4 \times 427 , \text{kJ/mol} = 1708 , \text{kJ/mol} \)
Total bond energy of products: \[ 1308 , \text{kJ/mol} + 1708 , \text{kJ/mol} = 3016 , \text{kJ/mol} \]
Step 3: Compare total bond energies.
- Total bond energy of reactants: 2612 kJ/mol
- Total bond energy of products: 3016 kJ/mol
Conclusion:
Since the total bond energy of the reactants (2612 kJ/mol) is less than that of the products (3016 kJ/mol), the reaction must absorb energy. Therefore, we conclude that:
The reaction is endothermic because the total bond energy of the reactants is less than the total bond energy of the products.
Correct Answer:
The reaction is endothermic because the total bond energy of the reactants is less than the total bond energy of the products.