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01/10/2021 11:25 am
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ΔHºf of water is -285.8 kJ mol-1. If enthalpy of neutralisation of monoacidic strong base is -57.3 kJmol-1. ΔHºf of OH- ion will be
(a) -114.25 kJ mol-1
(b) 114.25 kJ mol-1
(c) 228.5 kJ mol-1
(d) -228.5 kJ mol-1
1 Answer
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01/10/2021 11:42 am
Correct answer: (d) -228.5 kJ mol-1
Explanation:
H2(g) + 1/2O2(g) → H2O(l);
ΔH = -285.8 kJ .....(i)
H+(aq) + OH-(aq) → H2O(l);
ΔH = -57.3 kJ ......(ii)
\(\frac{1}{2}\)H2(g) + OH-(aq) → H+(aq) + e-;
ΔH = 0 (by convention) .....(iii)
(i) – (ii) – (iii) gives
\(\frac{1}{2}\)H2(g) + \(\frac{1}{2}\)O2(g) + e- + aq → OH-(aq)
ΔH = -285.8 + 57.3
= -228.5 kJ mol-1