Question

When a little sulfuric acid is added to water in a beaker, the water becomes hot.

Answer 1

The concentrated Sulphuric acid (${H_2}S{O_4}$) is a very strong acid and highly corrosive and due this property it is called as king of acids. It is also known as oil of vitriol. So, always remember that when strong acid reacts with water, the exothermic reaction will occur. Those reactions or processes that release energy are called exothermic reactions and in this process the energy will release in the form of heat or light. In this reaction, the total energy of the products is less than the total energy of the reactants so energy is released. Sulfuric acid is widely used in industrial purposes like in fertilizer, metal and chemical industries, refining of oil etc. In many reactions it is used for chemical synthesis and also an important component of acid rain.

Complete step by step answer:
When sulphuric acid is added to water, it donates ${H^ + }$ ions. These H+ ions combine with water molecules to form hydronium ions. This is an exothermic process ( every acid – base reaction is exothermic in nature and occurs very fast ) and a lot of heat energy is produced. Due to the heat generated the water becomes hot.

Additional information:
Exothermic reaction :
Heat is evolved in this case.
$\Delta H$ is negative as ${H_R} > {\text{ }}{H_p}$
$\Delta H{\text{ }} = {\text{ }}{H_p}-{H_R}$= –ve (At constant pressure)
$\Delta E{\text{ }} = {\text{ }}({E_p}-{E_R})$ = –ve (At constant volume)
${E_R} > {\text{ }}{E_P}$
Stability of a compound formed by exothermic reaction is more than that of a compound formed by endothermic reaction.

Note: Acid is a substance whose aqueous solution possessed the following characteristic properties :
(i) conducts electricity,
(ii) reacts with active metals like zinc, magnesium etc. to give hydrogen,
(iii) turns blue litmus red,
(iv) has a sour taste,
(v) whose acidic properties disappear on reaction with a base.
Arrhenius gave the definitions of acids as follows :
An acid is defined as a substance which contains hydrogen and which when dissolved into water gives hydrogen ions (${H^ + }$).
Examples. Substances like $HCl,{\text{ }}HN{O_3}$ and ${H_2}S{O_4}$, containing hydrogen, when dissolved in water dissociate completely into H+ ions and the negative ions.
An acid is a substance which donates a proton. Also remember that water is amphoteric in nature ( i.e, it can act as an acid or a base ).