Which from following reactions is exothermic?
Which from following reactions is exothermic?
Show Hint
\(\mathrm{KOH}_{(\mathrm{aq})}+\mathrm{HNO}_{3(\mathrm{aq})}\longrightarrow \mathrm{KNO}_{3(\mathrm{aq})}+\mathrm{H}_{2}\mathrm{O}\)
\(\mathrm{H}_{2}\mathrm{O}_{(\mathrm{s})}\longrightarrow \mathrm{H}_{2}\mathrm{O}_{(l)}\)
\(\mathrm{NaCl}_{(\mathrm{s})}+\mathrm{aq}\longrightarrow \mathrm{Na}_{(\mathrm{aq})}^{+}+\mathrm{Cl}_{(\mathrm{aq})}^{-}\)
\(\mathrm{N}_{2(\text{ }\mathrm{g})}+2\mathrm{O}_{2(\text{ }\mathrm{g})}\longrightarrow 2\mathrm{NO}_{2(\text{ }\mathrm{g})}\)
The Correct Option is A
Solution and Explanation
An exothermic reaction releases heat, with negative \(\Delta H\).
Step 2: Check Each Option
Neutralisation of \(\text{KOH}\) with \(\text{HNO}_3\) gives about \(-57\ \text{kJ mol}^{-1}\), so it is exothermic.
Melting of ice absorbs heat.
Dissolving \(\text{NaCl}\) is slightly endothermic.
Formation of \(\text{NO}_2\) from \(\text{N}_2\) and \(\text{O}_2\) is endothermic.
Step 3: Conclusion
Only the neutralisation reaction releases heat.
Final Answer:
The neutralisation of KOH by nitric acid is exothermic. \[ \boxed{\text{(A) }\text{KOH}_{(aq)} + \text{HNO}_{3(aq)} \rightarrow \text{KNO}_{3(aq)} + \text{H}_2\text{O}} \]
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