Question

Which of the following are exothermic processes?
A. Reaction of water with quicklime
B. Dilution of an acid
C. Evaporation of water
D. Sublimation of camphor (crystals)
1. A and B
2. B and C
3. A and D
4. C and D

Answer 1

The change of one or more substances into other substances having different composition and properties is called a chemical reaction. Reactions which release energy are called exothermic. Energy is released to the environment, so there is an increase in the temperature.

Complete step by step answer:
We know that all chemical reactions consist of breaking of bond and formation of bond. During breaking and formation of bonds, energy is either absorbed or released.
We know that heat is a form of energy. Exothermic reactions are those reactions in which heat is given out while endothermic reactions are those reactions in which heat is taken in.
Now let’s consider each reaction given in the problem.
A. Quick lime is another name for calcium oxide. Its molecular formula is ${{CaO}}$. When it is reacted with water molecules, it forms calcium hydroxide. Calcium hydroxide is also known as slaked lime. Here, heat energy is released. Thus it is an exothermic reaction.
B. During dilution of acid, there occurs two types of energy, i.e. dissociation energy and hydration energy. Dissociation energy is less than the hydration energy. This makes the reaction exothermic.
C and D. Evaporation of water and burning of camphor are endothermic reactions. We are giving heat for evaporating water molecules and burning of camphor molecules. During evaporation of water and burning of camphor, finally the reaction is cooled.

Hence, A and B are correct. So, option 1 is correct.

Note:
Production of slaked lime from quick lime is applied when we add water to dry cement. It forms concrete and also the mixture becomes so hot. We know that the condensation and evaporation needs the same temperature.