Question

What happens when a solution of an acid is mixed with a solution of a base in a test tube?
i. The temperature of the solution increases
ii. The temperature of the solution decreases
iii. The temperature of the solution remains the same
iv. Salt formation takes place.
a. $(i)$ only
b. $(i)$ and $(iii)$
c. $(ii)$ and $(iii)$
d. $(i)$ and $(iv)$

Answer 1

We know that, for the breaking of bonds, energy is required to be given in a reaction and if the bonds are forming, then energy is released in the reaction. Based on the breaking or forming bonds, the temperature change for the given case can be decided. Also, the reaction of acid and base is known as the neutralization reaction, which creates a neutral, non-basic, non-acidic solution.

Complete step by step answer:
The reaction of a solution of acid and a solution of base is known as the neutralization reaction.
In the neutralization, acid and base react with each other and give salt and water as products.
$Acid+Base\to Salt+Water$
Neutralization means the acid and base react with each other and produce a neutral product which is known as salt whose $pH$ is almost $7$ .
For example, Hydrochloric acid (Acid) reacts with Sodium Hydroxide (Base) and gives out Sodium Chloride (Salt) and water as products.
Thus, by reaction of acid and base, salt is obtained.
Now, acids and bases are electrolytes, strong or weak. Hence, when they are dissolved in an electrolytic solvent (like water), they get dissociated into ions. Hence, they break the ionic bond spontaneously and we aren't required to give energy from outside.
However, the ions of acid and base react to form an ionic salt and hydrogen ion and hydroxyl ion react to form the water molecule. As new bonds are formed in the water molecule, energy is produced or we can say heat is produced.
Due to the production of heat, known as Heat of neutralization, the temperature of the solution increases.

Hence, the correct answer is Option $(d)$.

Note:
Here, it is proved that the neutralization reaction is an exothermic reaction. However, there are certain exceptions where neutralization is endothermic. For example, the reaction of citric acid and sodium hydrogen carbonate. Also, energy required to break ionic bonds is not considered because the ionic bond is not a formal bond, it is an attractive force between the positive and negative charges, which is broken when dissolved in an electrolytic solvent. Thus, if a reaction of covalent compounds is considered, we have to take the energy required to break the bonds as well, because the covalent bond is a formal bond.