Question

How can the formation of a solution be exothermic or endothermic?

Answer 1

To solve this we must know that the process in which heat is released from the system to the surrounding is known as exothermic process. And the process in which heat is absorbed by the system from the surrounding is known as the endothermic process.

Complete step by step answer:
We know that a solution is formed when two or more substances having the same phase are mixed. To form a solution the molecules of solute must form bonds with the molecules of the solvent.
The three steps of solution formation are as follows:
1. Breaking of solute - Solute bonds.
2. Breaking of solvent - Solvent bonds.
3. Formation of solute - Solvent bonds to form a solution.

- During the first two steps, energy is absorbed and during the last step, energy is released. The formation of a solution can be exothermic or endothermic depending on the amounts of energy required to break the bonds and the amount of energy released upon the solute-solvent bond formation.
- If the amount of energy required to break the bonds is less than the amount of energy released upon the solute-solvent bond formation then the process is exothermic.
Example of exothermic process: Solution of sodium hydroxide in water.
- If the amount of energy required to break the bonds is more than the amount of energy released upon the solute-solvent bond formation then the process is endothermic.
Example of endothermic process: Solution of ammonium chloride in water.

Note: When the formation of a solution is exothermic i.e. heat is released from the system to the surrounding then the vessel in which the solution is prepared feels hot. When the formation of a solution is endothermic i.e. heat is absorbed by the system from the surrounding then the vessel in which the solution is prepared feels cold.