Chapter U3, Problem 3RE

Interpretation Introduction

Interpretation : Using kinetic theory of gases, reason for gas expanding when heated and contracting when cooled has to be explained.

Concept Introduction : Solids, liquids and gases have different arrangement of atoms and molecules. In solids and liquids they are held close together by intermolecular forces. Molecules in gases are far apart as there are no forces between molecules in a gas.

Answer to Problem 3RE

According to kinetic theory of gases, the gas particles are in constant random motion. The gas particles are constantly striking each other and the walls of the container. When the temperature increases, the average speed of the particles also increase. With increase in average speed, their collisions increase and they move farther apart. Their volume increases. This causes gases to expand on heating.

Similarly when temperature decreases, the gas particles come close together due to decease in their average speed and decrease in their number of collisions. This makes them shrink or contract.

Explanation of Solution

In order to explain the properties of gases such as motions of gas particles, scientists have proposed a model called kinetic theory of gases. The model proposed that the gas particles are in constant motion. The theory also explains that not all gas particles move at the same speed. This theory focuses on average speed for all particles at a given temperature. The temperature of a gas is a measure of the average kinetic energy of the gas particles.

When the temperature increases, the average speed of the particles also increase.The gas particles are constantly striking each other and the walls of the container. With increase in average speed, their collisions increase and they move farther apart. Their volume increases. This causes gases to expand on heating.

Similarly when temperature decreases, the gas particles come close together due to decease in their average speed and decrease in their number of collisions. This makes them shrink or contract.

Conclusion

Temperature is a measure of the average speed of the atoms or molecules in a sample.