Explanation:

When an ideal gas undergoes unrestrained expansion, there is no external work done on the gas, and hence, no heat is exchanged between the gas and the surroundings. The temperature of the gas remains constant during the expansion process. However, the volume of the gas increases, and hence, the density of the gas decreases. This leads to a decrease in the frequency of collisions between the gas molecules.

The reason why no cooling occurs during the expansion of an ideal gas is because the gas molecules exert no attractive force on each other. This means that there is no energy lost due to intermolecular forces during the expansion process.

To understand this concept better, let us consider the following points:

- Intermolecular forces: In a real gas, the molecules attract each other due to intermolecular forces. These forces cause the gas molecules to stick together, and hence, they require energy to be separated from each other. During the expansion of a real gas, some energy is lost due to these intermolecular forces, and hence, the temperature of the gas decreases.

- Ideal gas: On the other hand, an ideal gas is a theoretical concept, where the gas molecules do not interact with each other at all. They move around randomly, colliding elastically with each other and with the walls of the container. In an ideal gas, there are no intermolecular forces, and hence, no energy is lost due to these forces during the expansion process.

- Work done: When an ideal gas expands, it does work against the external pressure. This work is equal to the loss in kinetic energy of the gas molecules. However, since there are no intermolecular forces in an ideal gas, there is no loss in kinetic energy during the expansion process. Hence, no work is done, and no cooling occurs.

- Adiabatic expansion: An adiabatic expansion is one where no heat is exchanged between the system and the surroundings. In an adiabatic expansion of an ideal gas, the temperature of the gas decreases because the gas molecules lose kinetic energy due to the work done against the external pressure. However, in an unrestrained expansion, there is no external pressure, and hence, no work is done, and the temperature of the gas remains constant.

In conclusion, the reason why no cooling occurs during the unrestrained expansion of an ideal gas is because the gas molecules exert no attractive force on each other, and hence, there is no loss of energy due to intermolecular forces during the expansion process.