Final answer:
The change in enthalpy (ΔH) measures the energy difference between reactants and products in a chemical reaction, indicating whether the reaction absorbs or releases energy. When ΔH is negative, it means the reaction releases energy, typically as heat, and is exothermic because the products contain stronger bonds than the reactants.
Step-by-step explanation:
The change in enthalpy of a reaction, represented by ΔH, indicates whether energy is absorbed or released during a chemical reaction. It is calculated as the difference in total energy of the reactants and products. When breaking chemical bonds in reactants, energy is consumed (positive ΔH), and when forming new bonds in the products, energy is released (negative ΔH). If more energy is required to break bonds than is released during bond formation, the reaction is endothermic and ΔH is positive. Conversely, if more energy is released during bond formation than is consumed to break bonds, the reaction is exothermic and ΔH is negative.
In the context of a chemical reaction that releases more energy than it absorbs, ΔH is negative, indicating that the bond energies of the products are stronger than those of the reactants, and the reaction is exothermic. This excess energy is typically released as heat energy, showing up on the product side of the equation. The enthalpy change can be calculated by subtracting the bond dissociation energies of the products from those of the reactants (ΔH = Σ (bond dissociation energies reactants) - Σ (bond dissociation energies products)).