Question

48. The heat of neutralisation of HCl by NaOH is
-55.9 kJ/mole. If the heat of neutralization of HCN by
NaOH is –12.1 kJ/mole, the energy of dissociation
of HCN is
(1) 43.8 kJ
(2) 43.8 kJ
(3) 68 kJ
(4) -68 kJ
10 Molhoot one​

Answer 1

The energy of dissociation of HCN is 43.8 kJ/mole

Explanation:

$HCl+NaOH\rightarrow NaCl+H_2O$     $\Delta H=-55.9$ kJ/mole

We know that heat of neutralization of strong acid, strong base is heat of formation of water

Therefore,

$H^++OH^-\rightarrow H_2O$     $\Delta H=-55.9$ kJ/mole

or, $H_2O\rightarrow H^++OH^-$     $\Delta H=55.9$ kJ/mole    ...(1)

As given, heat of neutralization of of HCN y NaOH is 12.1 kJ/mole

Therefore,

$HCN+OH^-\rightarrow H_2O+CN^-$      $\Delta H=-12.1$ kJ/mole    ....(2)

Adding eq (1) and (2)

$HCN\rightarrow H^++CN^-$     $\Delta H=55.9-12.1=43.8$ kJ/mole

Hence, the energy of disassociation of HCN is 43.8 kJ/mole

Hope this answer is helpful.

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