Final answer:
The reaction ΔHrxn is negative in the combustion of octane, indicating that it is an exothermic reaction where energy is released as heat.
Step-by-step explanation:
In the combustion reaction of octane (C₈H₁₈) in air, the reaction is exothermic because the energy of the product water and carbon dioxide is lower than that of the reactants. This results in a negative ΔHrxn, indicating that energy is released during the reaction. In thermochemistry, the negative ΔH signifies that the reactants have a higher enthalpy than the products, thereby releasing heat to the surroundings when the reaction occurs. The bonds in the products are stronger and more stable than those in the reactants, which is typical for an exothermic combustion process.