Concept:An endothermic reaction absorbs heat (\( \Delta H > 0 \)), while an exothermic reaction releases heat (\( \Delta H < 0 \)).
Formula:$$ CH_{4(g)} + 2O_{2(g)} \rightarrow CO_{2(g)} + 2H_2O_{(l)} \quad \Delta H = -890 \text{ kJ/mol} $$
Solution:- Combustion of methane involves burning natural gas in oxygen. This process releases massive amounts of heat and light energy.
- Because it releases heat, it is strictly an exothermic reaction, making it the correct answer to what is "not endothermic".
Why other options are incorrect:Decomposition of water requires an input of electrical energy (endothermic). Dehydrogenation requires high heat to break C-H bonds (endothermic). Graphite is more stable than diamond, so converting it requires a massive energy input (endothermic).
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