Final answer:
The enthalpy change for a chemical reaction can be calculated by summing the energy required to break the bonds in the reactants and the energy released when new bonds are formed in the products.
Step-by-step explanation:
The enthalpy change, ΔH, for a chemical reaction is approximately equal to the sum of the energy required to break all bonds in the reactants (energy "in", positive sign) plus the energy released when all bonds are formed in the products (energy "out," negative sign). This can be expressed mathematically as follows:
ΔH = ΣDbonds broken - ΣDbonds formed
In this equation, ΣD represents the bond energy in kilojoules per mole, which is always a positive number obtained from a table. The values depend on the type of bond (single, double, or triple bond). By considering the bonding in all reactants and products, this calculation provides an estimate, not an exact value, for the enthalpy of the reaction.