Concept:The total energy or enthalpy of a chemical system dictates whether a reaction will release or absorb heat. This is visualized on a potential energy diagram.
Formula:$$ \Delta H = E_{\text{products}} - E_{\text{reactants}} $$
Solution:- If the reactants possess higher internal energy than the products (\( E_R > E_P \)), the excess energy must be released into the surroundings as heat.
- A reaction that releases heat to the surroundings is strictly classified as an exothermic reaction.
- The result is a more stable product and a negative \( \Delta H \).
Why other options are incorrect:In endothermic and photochemical reactions, energy is actively absorbed, meaning the products end up with a higher energy than the reactants (\( E_P > E_R \)).
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