Question

Match the following (Assume heat of neutralisation of strong acid with strong base is 13.7 kcal):

$\begin{array}{cccc}& \text{Column - I}& & \text{Column - II}\\ & \text{(Enthalpy change in kcal)}& & \text{(Neutralisation)}\\ \text{(A)}& <13.7\text{kcal}& \text{(p)}& \underset{\left(1mol\right)}{HCl}+\underset{\left(1mol\right)}{NaOH}\\ \text{(B)}& =13.7\text{kcal}& \text{(q)}& \underset{\left(1mol\right)}{HF}+\underset{\left(1mol\right)}{NaOH}\\ \text{(C)}& >13.7\text{kcal}& \text{(r)}& \underset{\left(1mol\right)}{N{H}_{4}OH}+\underset{\left(1mol\right)}{HCl}\\ \text{(D)}& =27.4\text{kcal}& \text{(s)}& \underset{\left(2mol\right)}{NaOH}+\underset{\left(1mol\right)}{H_{2}S{O}_4}\\ & & \text{(t)}& \underset{\left(1mol\right)}{NaOH}+\underset{\left(1mol\right)}{C{H}_{3}COOH}\end{array}$

• A. a - r, t
  b - p
  c - q, s
  d - s
• B. a - r, t,s
  b - p
  c - q,
  d - s
• C. a - r, t,s
  b - p,s
  c - q, s
  d - s
• D. a - r, t
  b - p,s
  c - q, s
  d - p

Answer 1

The correct option is A a - r, t

b - p
c - q, s
d - s
Point to remember:
$\Rightarrow$For Strong $Acid+StrongBase$, heat of neutralisation is always equal to $–13.7kcal/mole$ or $–57.1kJ/mole$.
$\Rightarrow$ For any other combination it must be less than $–13.7kcal/mole$ or $–57.1kJ/mole$.
$\Rightarrow$ Rest of energy utilised for ionisation of weak acid or base
For
$HCl+NaOH$
Both are strong so $\Delta H=13.7kcal$

For
$\underset{1mole}{HF}+\underset{1mole}{NaOH}$
$HF$ weak acid thus $\Delta H\le 13.7kcal$

For
$\underset{1}{N{H}_{4}OH}+\underset{1}{HCl}$
weak base and strong acid so $\Delta H\le 13.7kcal$

For
$\underset{2}{NaOH}+\underset{1}{H_{2}S{O}_4}$
two mole of $\left[H^{+}\right]$ reacting with two mole of $\left[O{H}^{-}\right]$ so $\Delta H=27.4kcal$

For
$\underset{1}{C{H}_{3}COOH}+\underset{1}{N{H}_{4}OH}$
both are weak acid so $\Delta H\le 13.7kcal$