Question

$150{\text{ ml}}$ of $0.5{\text{ N}}$ nitric acid solution at ${25.35^ \circ }{\text{C}}$ was mixed with $150{\text{ ml}}$ of $0.5{\text{ N}}$ sodium hydroxide solution at the same temperature. The final temperature was recorded to be ${28.77^ \circ }{\text{C}}$. The heat of neutralisation of nitric acid with sodium hydroxide is:
A) $ - 12.64{\text{ kcal}}$
B) $ - 11.98{\text{ kcal}}$
C) $ - 13.68{\text{ kcal}}$
D) $ - 12.68{\text{ kcal}}$

Answer 1

Hint: The heat of reaction released during the neutralisation of an acid or a base is known as the heat of neutralisation. The neutralisation reaction is an exothermic reaction. in a neutralisation reaction, strong acid and strong base completely dissociates in the solution.

Formulae Used:
$Q = mc\Delta T$
${\text{Heat of neutralisation}} = \dfrac{Q}{{MV}}$

Complete step by step answer:
$150{\text{ ml}}$ of nitric acid solution at ${25.35^ \circ }{\text{C}}$ was mixed with $150{\text{ ml}}$ of sodium hydroxide solution at the same temperature.
Thus, the total mass of the solution is,
${\text{Total mass of the solution}} = \left( {150 + 150} \right){\text{ mL}}$
${\text{Total mass of the solution}} = 300{\text{ mL}}$
Thus, the total mass of the solution is $300{\text{ mL}}$.
Calculate the heat required using the equation as follows:
$Q = mc\Delta T$
Where Q is the heat energy,
m is the mass of the solution,
c is the specific heat,
$\Delta T$ is the change in temperature.
Thus,
$Q = 300 \times 1 \times \left( {28.77 - 25.35} \right)$
$Q = 1026{\text{ cal}}$
Thus, the heat required is $1026{\text{ cal}}$.
Calculate the heat of neutralisation using the equation as follows:
${\text{Heat of neutralisation}} = \dfrac{Q}{{MV}}$
Where $Q$ is the heat energy,
N is the normality of the solution,
V is the volume.
${\text{Heat of neutralisation}} = \dfrac{{1026}}{{0.5 \times 150}}$
${\text{Heat of neutralisation}} = 0.01368{\text{ cal}} = 13.68{\text{ kcal}}$
Thus, the heat of neutralisation is $ - 13.68{\text{ kcal}}$.

Thus, the correct option is (C) $ - 13.68{\text{ kcal}}$.

Note: The negative sign of the value of the heat of neutralisation is because the neutralisation reaction is an exothermic reaction. In an exothermic reaction, heat is released. If the reaction is endothermic and heat is absorbed in the reaction, the value has a positive sign. The complete dissociation of strong acids and strong bases occurs during a neutralisation reaction. A strong covalent bond is then formed between hydrogen and the hydroxide ions to form water molecules. This bond formation process releases a large amount of heat. Thus, the neutralisation reaction is an exothermic process.