Concept:The sign convention for the change in enthalpy (\( \Delta H \)) is rooted in the system's perspective. Loss of energy to the surroundings is a negative change for the system.
Formula:$$ \Delta H = H_{\text{products}} - H_{\text{reactants}} $$
Solution:- In an exothermic reaction, the chemical system releases energy into the surroundings as heat.
- This means the final internal enthalpy of the products is lower than the initial internal enthalpy of the reactants (\( H_P < H_R \)).
- Subtracting a larger number from a smaller number results in a mathematical deficit, so \( \Delta H \) must strictly be written as Negative.
Why other options are incorrect:A positive \( \Delta H \) means energy was absorbed (endothermic). Zero means no net heat exchange occurred (isothermic). Constant implies no change, which contradicts a chemical reaction occurring.
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