Final answer:
In an exothermic reaction, reactants have a higher heat content compared to products; excess heat is released, making ΔHrxn a negative quantity.
Step-by-step explanation:
In an exothermic reaction, the reactants have a higher heat content than the products, and the excess heat is released during the reaction; thus ΔHrxn is a negative quantity. This is because exothermic reactions involve the formation of products that have stronger bonds than the reactants, indicating that the energy of the products is lower than that of the reactants.
Hence, the reaction is considered energetically downhill. The energy, often in the form of heat, is given off as the system releases excess heat to its surroundings, making them warm. The enthalpy change of the reaction, denoted as ΔH, is negative in an exothermic reaction, representing a release of energy.