Question

The enthalpy of neutralisation of $NH_{4}OH\text{and}CH_{3}COOH$ is $-10.5kcalmol^{- 1}$ and enthalpy of neutralisation of $CH_{3}COOH$ with strong base is $-12.5kcalmol^{- 1}$ .The enthalpy of ionisation of $NH_{4}OH$ will be

• A. $4.0kcalmol^{- 1}$
• B. $3.0kcalmol^{- 1}$
• C. $2.0kcalmol^{- 1}$
• D. $3.2kcalmol^{- 1}$

Answer 1

Answer: (C)

$\Delta \text{H} _{\text{neutr.}} \text{for strong acid with strong base} = - 1 3 \cdot 7 \text{kcal equiv}^{-1}$
Enthalpy of ionisation of acetic acid & NH₄OH together
$= - \text{10} \text{.5} - \left(\right. - \text{13} \text{.7} \left.\right) = + \text{3} \left(\text{.2 kcal mol}\right)^{\text{-1}}$
Enthalpy of ionisation of only acetic acid
$= - \text{12} \text{.5} - \left(\right. - \text{13} \text{.7} \left.\right) = + \text{1} \left(\text{.2 kcal mol}\right)^{\text{-1}}$
Enthalpy of ionisation of only NH₄OH
$= \text{3} \text{.2} - \text{1} \text{.2} = \text{2 kcal mol}^{\text{-1}}$