Question
Question: The heat of neutralisation of HCl by NaOHis – 55.9 kJ mol<sup>–1</sup>. If the heat of neutralisatio...
The heat of neutralisation of HCl by NaOHis – 55.9 kJ mol–1. If the heat of neutralisation of HCN by NaOH is – 12.1 kJ/mol, the energy of dissociation of HCN is:
A
– 43.8 kJ
B
43.8 kJ
C
68 kJ
D
– 68 kJ
Answer
43.8 kJ
Explanation
Solution
Since neutralisation is an exothermic process, so the sign of its heat is
–ve. As we know, for weak acid, some amount of heat is used to dissociate it.
i.e, heat of dissociation (for weak acid) + heat of ionization = heat of ionization for strong acid with strong base, NaOH.
Heat of dissociation ( for weak acid) + 12.1 = 55.9
∴ heat of dissociation (for weak acid) = 55.9 – 12.1 = 43.8 kJ