Concept:When a chemical reaction releases heat energy, that energy is transferred to the immediate surroundings (the system's medium), resulting in an observable rise in temperature.
Formula:$$ CaO_{(s)} + H_2O_{(l)} \rightarrow Ca(OH)_{2(aq)} \quad \Delta H = -\text{ve} $$
Solution:- Quick lime (\( CaO \)) reacts vigorously with water to form slaked lime (\( Ca(OH)_2 \)).
- The question states there is a "rise in the temperature of the system", which is the hallmark macroscopic observation of heat being evolved.
- Reactions that evolve heat are exothermic (\( \Delta H < 0 \)).
Why other options are incorrect:Endothermic reactions absorb heat and cause a drop in temperature. Reaction order (Third order) describes kinetics, not thermodynamics. The reaction is highly spontaneous, ruling out non-spontaneous.
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