To determine whether the given reaction is exothermic or endothermic, 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.
Bonds Broken: (Reactants) CH4 + 4Cl2
- 4 H–C: 4 × 411 kJ/mol = 1644 kJ
- 4 Cl–Cl: 4 × 0 kJ/mol (since Cl2 is a diatomic molecule and bond energy is 0 for bonds that do not exist)
Total Energy of Bonds Broken: = Energy for H-C bonds + Energy for Cl-Cl bonds = 1644 kJ + 0 = 1644 kJ
Bonds Formed: (Products) CCl4 + 4HCl
- 4 C–Cl: 4 × 327 kJ/mol = 1308 kJ
- 4 H–Cl: 4 × 427 kJ/mol = 1708 kJ
Total Energy of Bonds Formed: = Energy for C-Cl bonds + Energy for H-Cl bonds = 1308 kJ + 1708 kJ = 3016 kJ
Now we compare the total energies:
- Total energy of bonds broken = 1644 kJ
- Total energy of bonds formed = 3016 kJ
Net Energy Change = Total Energy of Bonds Broken - Total Energy of Bonds Formed = 1644 kJ - 3016 kJ = -1372 kJ
Since the net energy change is negative, this indicates that the reaction releases energy, making it exothermic.
Thus, the correct response is: The reaction is exothermic because the total bond energy of the reactants is less than the total bond energy of the products.
The incorrect responses can be identified as follows:
- "The reaction is exothermic because the energy of each bond in the reactants is greater than the energy of a bond in the products." is incorrect because we are concerned with total energy, not individual bond energies.
- "The reaction is endothermic because the total bond energy of the reactants is greater than the total bond energy of the products." is false; it is exothermic, as shown by the calculations.
- "The reaction is endothermic because the energy of each bond in the reactants is less than the energy of a bond in the products." is also incorrect, as analyzed in the energy calculation.
Therefore, the final conclusion and the correct statement should encapsulate the overall energy comparison rather than individual bond comparisons.