Question

Identify which of the following is an exothermic process?
A. Dilution of sulphuric acid
B. Sublimation of dry ice
C. Evaporation of water
D. Melting of ice

Answer 1

Those chemical reactions which release energy as they move towards the product side are known as exothermic reactions. One of the best examples of an exothermic reaction that can be observed in your home is when the mixture of honey with calcium carbonate (chuna) is added onto a sore throat, the reaction releases heat and gives a soothing effect.

Complete solution:
The energy is released in the form of heat in an exothermic reaction.Now Let’s observe the given options;
i. Dissolution of sulphuric acid is the chemical reaction in which acid is added to water, to make a solution of dilute sulphuric acid, this reaction is exothermic because the formation of hydrogen bonding with the water molecules releases energy and this energy is then absorbed by the water molecules.Therefore this option is the correct one, but let’s kindle the light of knowledge and look at the other options and their reaction types.
ii. Sublimation is the process of conversion of one state of matter i.e, solid to another i.e., gas without being transitioned into the liquid state. Sublimation of dry ice (solid carbon dioxide) is an endothermic reaction as the heat of the surrounding is used to complete the process.
iii. Evaporation of water is another phase change reaction from liquid to gas, also known as boiling, this reaction is also endothermic, as we provide heat to break the bonds between the water molecules.
iv. Melting of ice is also an endothermic reaction as when the ice melts from solid-state to liquid state the surrounding atmosphere observes a drop in temperature.
Therefore, from the above explanation we can say that the correct option is (A).

Note: Remember in the process of dissolution is acid, we add the acid to the water not the other way around (i.e., Adding water to acid). Because in the first case we have enough water molecules to absorb the released heat during the reaction. But in the second a small amount of water compared to the amount of acid present in the solution, which would be highly exothermic and will result in an explosion as there would be no molecules to absorb the released heat.