Question

1.0 L of 1.0 M sodium hydroxide is neutralized by 1.0 L of 1.0 M methanoic acid. If the heat of formation of water is X then the heat of neutralization of this reaction is

• A. less than X
• B. more than X
• C. equal to X
• D. none of these

Answer 1

Answer: (A)

Heat of neutralisation of a strong acid with strong base is constant and near the equal to 13.7 kcal. Here constant value represents the heat of formation of one mole of water.
$ {{H}^{+}}+O{{H}^{-}}\xrightarrow[{}]{{}}{{H}_{2}}O, $
$ \Delta H=13.7\text{ }kcal $
But the heat of neutralisation of weak acid (such as methanoic acid) and strong base (such as NaOH) is less than 13.7 kcal (X) because some heat is utilized to dissociate the molecule of weak acid into ions.