To determine whether the reaction is exothermic or endothermic, we need to calculate the total bond energies of the reactants and products.
Given:
- Reaction: \( \text{CH}_4 + 4 \text{Cl}_2 \rightarrow \text{CCl}_4 + 4 \text{HCl} \)
Bond Energies:
-
Breaking Bonds (Reactants):
- 4 x \( \text{H–C} \) = 4 × 411 kJ/mol = 1644 kJ
- 4 x \( \text{Cl–Cl} \) = 4 × 242 kJ/mol = 968 kJ
Total Energy of Bonds Broken (Reactants): \[ 1644 , \text{kJ} + 968 , \text{kJ} = 2612 , \text{kJ} \]
-
Forming Bonds (Products):
- 4 x \( \text{C–Cl} \) = 4 × 327 kJ/mol = 1308 kJ
- 4 x \( \text{H–Cl} \) = 4 × 427 kJ/mol = 1708 kJ
Total Energy of Bonds Formed (Products): \[ 1308 , \text{kJ} + 1708 , \text{kJ} = 3016 , \text{kJ} \]
Analysis:
- Total Energy of Bonds Broken (Reactants): 2612 kJ
- Total Energy of Bonds Formed (Products): 3016 kJ
Change in Energy:
- The energy required to break the reactants (2612 kJ) is less than the energy released during the formation of the products (3016 kJ).
Conclusion:
Since the total bond energy of products (3016 kJ) is greater than the total bond energy of reactants (2612 kJ), the reaction releases energy, indicating that it is exothermic.
Thus, the correct answer is: The reaction is exothermic because the total bond energy of the reactants is less than the total bond energy of the products.