Concept:The change in enthalpy (\( \Delta H \)) represents the heat absorbed or released by a system at constant pressure. The sign convention is determined by the direction of heat flow.
Formula:$$ \Delta H = H_{\text{products}} - H_{\text{reactants}} $$
Solution:- In an exothermic reaction, the system loses heat to the surroundings.
- Because the energy of the products is lower than the energy of the reactants, the final enthalpy is less than the initial enthalpy.
- Mathematically, this results in a negative value: \( \Delta H = -ve \).
Why other options are incorrect:Endothermic, dissociation, and decomposition reactions generally require an input of energy to break chemical bonds, meaning they absorb heat from the surroundings and have a positive \( \Delta H \).
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