Final answer:
In the reaction to form water (2H₂ + O₂ → 2H₂O), the bond breaking involves two H-H bonds in hydrogen and one O=O bond in oxygen, which are broken to allow the formation of new O-H bonds in water molecules.
Step-by-step explanation:
In the chemical reaction 2H₂ + O₂ → 2H₂O, bond breaking occurs when the reactants (hydrogen and oxygen gases) are transformed into the product (water). Specifically, the bonds that are broken include two H-H bonds in the hydrogen molecules (H₂) and one O=O double bond in the oxygen molecule (O₂). These bonds are broken to form new bonds in the creation of water molecules, where each water molecule consists of an oxygen atom bonded to two hydrogen atoms, represented by O-H bonds.
To illustrate, we can examine the bond energies involved: breaking each H-H bond requires 105 kcal/mol, and breaking an O=O double bond requires 119 kcal/mol. This energy is then utilized to form new O-H bonds, each having a bond energy of 110 kcal/mol, resulting in two water molecules with a total of four O-H bonds.