Concept:Reactions are categorized by their heat exchange. Exothermic processes release heat (\( \Delta H < 0 \)) to the surroundings.
Formula:$$ C_{(s)} + O_{2(g)} \rightarrow CO_{2(g)} \quad \Delta H = -393.5 \text{ kJ/mol} $$
Solution:- Burning of coal is a highly energetic combustion reaction. Carbon reacts with oxygen to form highly stable carbon dioxide bonds, releasing massive amounts of heat and light. This is definitively an exothermic chemical reaction.
- Note: Freezing and condensation are exothermic physical phase changes, but combustion is universally recognized as the primary exothermic chemical reaction in this context.
Why other options are incorrect:Melting of ice is an endothermic phase change (absorbs heat). While freezing and condensation release heat, "burning of coal" is the textbook chemical reaction sought by the examiner.
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