Exothermic reactions and bond energies

Steps:

• Identify the reaction as exothermic, so ΔH < 0 (heat released).
• Recall ΔH = (total energy to break bonds) - (total energy to form bonds).
• For ΔH negative, energy to break bonds < energy to form bonds.
• Thus, total bond formation energy > total bond breaking energy.

Why A is correct:

• Exothermic reactions have ΔH < 0, meaning energy released from bond formation exceeds energy input for bond breaking, per the bond energy equation.

Why the others are wrong:

• B: This describes endothermic reactions (ΔH > 0), where bond breaking requires more energy.
• C: Exothermic reactions release heat, so temperature rises, not falls.
• D: Heat release causes temperature to increase, not remain unchanged.

Final answer: A