Chemistry – Chemical energetics - Exothermic and endothermic reactions | e-Consult

(a) The main exothermic pathway represents an exothermic reaction. This is because the energy released in the reaction is greater than the energy required to break the bonds in the reactants. Exothermic reactions release heat into the surroundings, resulting in a negative enthalpy change (ΔH

(b) The intermediate pathway represents an endothermic reaction. This is because energy is required to break the bonds in the reactants and initiate the reaction. Endothermic reactions absorb heat from the surroundings, resulting in a positive enthalpy change (ΔH > 0). The diagram shows an increase in energy as the reaction proceeds, indicating energy is absorbed.

(c) The units for the enthalpy change of reaction (ΔH) are kJ/mol (kilojoules per mole).