Which of the following best describes how to calculate the heat of reaction (ΔH) using bond energies and Lewis structures?

• A. Subtract the total bond energies of bonds broken in reactants from the total bond energies of bonds formed in products.
• B. Subtract the total bond energies of bonds formed in products from the total bond energies of bonds broken in reactants.
• C. Add the total bond energies of all bonds present in both reactants and products.
• D. Multiply the number of sigma and pi bonds in the products by their respective bond energies.

Answer: (B)

Verified step by step guidance

1. Understand that the heat of reaction (\( \Delta H \)) can be estimated by comparing the bond energies of bonds broken and bonds formed during the reaction.
2. Identify all the bonds broken in the reactants and sum their bond energies. Breaking bonds requires energy input, so this value is positive.
3. Identify all the bonds formed in the products and sum their bond energies. Forming bonds releases energy, so this value is considered negative when calculating \( \Delta H \).
4. Use the formula for the heat of reaction based on bond energies: \[ \Delta H = \sum \text{(bond energies of bonds broken)} - \sum \text{(bond energies of bonds formed)} \]
5. Calculate \( \Delta H \) by subtracting the total bond energy of bonds formed from the total bond energy of bonds broken, which gives the net energy change of the reaction.