Question

Equal volumes of molar hydrochloric acid and sulphuric acid are neutralised by dilute $NaOH$ solution and $x$ kcal and $y$ kcal of heat are liberated respectively. Which of the following is true?

• A. $x = y$
• B. $x=\frac{y}{2}$
• C. $x = 2y$
• D. none of the above

Answer 1

Answer: (B)

Heat of neutralisation = Heat of formation of water (1 mol)
$HCl + NaOH \longrightarrow NaCl + H _{2} O ; \,\,\,\Delta H=-x$
or $\underset{1 mol }{ H }^{+}+\underset{1 mol }{ OH ^{-}} \longrightarrow \underset{1 mol }{H_2O} ;$ $\Delta H=x$
$H _{2} SO _{4}+2 NaOH \rightarrow Na _{2} SO _{4}+2 H _{2} O ; \Delta H=-y$
or $2 H ^{+}+2 OH ^{-} \longrightarrow 2 H _{2} O ; \Delta H=-y$
$H ^{+}+ OH ^{-} \longrightarrow H _{2} O ; \Delta H=-\frac{y}{2}$
$\Rightarrow \Delta H=\Delta H$
$\therefore x=\frac{y}{2}$