Question

Which of the following are exothermic processes?

I. Reaction of water with quicklime

II. Dilution of acid

III. Evaporation of water

IV. Sublimation of camphor (Crystals)

• A. I and II
• B. II and III
• C. I and IV
• D. III and IV

Answer 1

The correct option is A

I and II

Based on the energy change, reactions can be of two types:

1. Exothermic reaction: The reaction in which heat energy is released is called an exothermic reaction.
2. Endothermic reaction: The reaction in which heat energy is required to complete the reaction is called an endothermic reaction.

The explanation for the correct option:

Option A:

1. Statement I: Quicklime is Calcium Oxide$\left(\mathrm{CaO}\right)$ and when it reacts with water$\left({\mathrm{H}}_2\mathrm{O}\right)$ it gives Calcium hydroxide$\left(\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\right)$ (Slaked Lime) along with the evolution of heat. This indicates that the reaction is exothermic.
2. The reaction can be shown as follows: $\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+∆$
3. Statement II: Dilution of acid is done by adding acid to water slowly. While doing this process if we touch the beaker, the heat can be felt. That means this process is an exothermic reaction as it releases heat during the reaction.

Hence, Statements I and II are exothermic processes.

The explanation for the incorrect options:

Statement III: In the evaporation of water, the water changes its state from a liquid state to a gaseous state. This is only possible if heat is given to water.

Hence, absorption of heat occurs during this process. So, it is an endothermic process.

Statement IV: In the sublimation of camphor, the state of camphor changes from solid to gas. This can happen only in the presence of heat.

This indicates that it needs heat for the process to occur so it is an endothermic process.

Options B, C, and D include statements III or IV or both. So, these options are incorrect.

Hence, Option A is the correct answer., Statement I and II.