Question

When $400mL$ of $0.2N$ solution of a weak acid is neutralised by a dilute aqueous solution of sodium hydroxide under standard conditions, $4.4kJ$ amount of heat is liberated. Therefore, the standard enthalpy bf neutralisation of this weak acid, in $kJ$ equiv ${}^{-1}$, is

• A. $-11$
• B. $-44$
• C. $-55$
• D. $-22$

Answer 1

Answer: (C)

Heat of neutralisation is the heat that evolved when one equivalent of acid is neutralised by one equivalent of a base.
$\because$ Milliequivalents of weak acid $=400\times 0.2$
$=80$ milliequivalents $\therefore$ Equivalents of the acid $=0.08$ equivalent.
Since, heat evolved when $0.08$ equivalent of acid is neutralised
$=4.4kJ$
$\therefore$ The heat evolved, when $1$ equivalent is neutralised
$=\frac{4.4\times 1}{0.08}=55kJ$ equiv ${}^{-1}$.