In an exothermic reaction the enthalpy change is
Correct answer: A. negative, because the products have less enthalpy than the reactants
- A. negative, because the products have less enthalpy than the reactants
- B. positive, because heat is released
- C. always zero
- D. negative, because the products have more enthalpy than the reactants
Explanation
Energy leaves the system as heat, so the products end up at a lower enthalpy and the difference, products minus reactants, is negative. The sign convention is taken from the point of view of the system, which is why released heat carries a minus sign even though the surroundings get warmer. Combustion and neutralisation are the standard exothermic examples.
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About Exothermic and Endothermic Reactions
Exothermic reactions release heat to the surroundings and have negative enthalpy change, while endothermic reactions absorb heat and have positive enthalpy change. The topic uses energy profiles to identify reactants, products and activation energy, and includes bond energy, enthalpy diagrams, calorimetry and Hess's law for calculating overall heat changes.
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