For the reaction 2H₂O → 2H₂ + O₂, what is the energy released by forming the product bonds using the bond energies H-H = 436 kJ/mol and O=O = 498 kJ/mol?

What “energy released by forming bonds” means

Bond formation releases energy. So you only add up the bond energies of the new bonds that appear in the products.

Count the bonds in the products

From the equation $2H_2O \rightarrow 2H_2 + O_2$:

• $2H_2$ contains $2$ H-H bonds total (each $H_2$ molecule has one H-H bond)
• $O_2$ contains $1$ O=O bond

Add the bond energies for the bonds formed

Using the table values:

• H-H: $436\ \text{kJ/mol}$
• O=O: $498\ \text{kJ/mol}$

Total energy released by forming product bonds: $$2(436) + 498 = 872 + 498 = 1370\ \text{kJ/mol}$$

Final check

You used only product bonds (formed bonds), so the result is a positive energy release value: $1370\ \text{kJ/mol}$ for the reaction as written.