Question

Addition of ${H_2}S{O_4}$ to water is
(A) An exothermic reaction
(B) An endothermic reaction
(C) A redox reaction
(D) A neutralisation reaction

Answer 1

Hint: Sulphuric acid, known as the king of chemicals is a very strong acid which is soluble in water. Let us recall the definition of each term given in the options and try to figure out the correct answer.

Complete answer:
A reaction in which heat is liberated is known as an exothermic reaction. “Exo” means “out” and “therm” means “heat”. Endothermic is the exact opposite. “Endo” means “in”. So if there is absorption of heat then it is known as endothermic reaction. Redox reaction is a type of chemical reaction in which reduction and oxidation occur simultaneously. Reduction is defined as the removal of oxygen or addition or hydrogen or gain of electrons whereas oxidation is addition of oxygen or removal of hydrogen or loss of electrons. If these two occur simultaneously, such a reaction is called a redox reaction. Lastly, neutralisation is a reaction between an acid and a base to produce salt and water.
Now we know what each term given in the option means. Let us see what happens when sulphuric acid is added to water. As it is a strong acid, it undergoes complete dissociation. That is, it splits up into opposite charges as
${H_2}S{O_4} \to 2{H^ + } + S{O_4}^{2 - }$
As there is no redox reaction or neutralisation occurring, we can eliminate options (C) and (D). This dissociation is highly exothermic. That is, the amount of energy absorbed by the acid to undergo dissociation is much less than the energy released after dissociation.

Hence the correct answer is option (A).

Note: As the reaction is highly exothermic, it is always advised to add acid slowly to water while making an aqueous solution and not the other way around.