alleryThe standard enthalpy of neutralisation of any strong acid by any strong base in dilute aqueous solution is approximately constant at:
A$-285.8\,\text{kJ mol}^{-1}$
B$+57.1\,\text{kJ mol}^{-1}$
C$-57.1\,\text{kJ mol}^{-1}$
D$0$
Answer & Solution
Correct answer: C. $-57.1\,\text{kJ mol}^{-1}$
Strong acids and strong bases are fully ionised in dilute aqueous solution
so the only net chemical change on neutralisation is $\mathrm{H^+(aq) + OH^-(aq) \to H_2O(l)}$, regardless of which strong acid or base is used.
The enthalpy change of this single reaction is approximately $-57.1\,\text{kJ mol}^{-1}$.
For weak acids or weak bases the value is lower in magnitude because energy is consumed in ionising the weak species.
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