Behaviour of a Fixed Quantity of Gas under Conditions of Varying Pressure, Volume and Temperature

The behaviours of gases can be explained through the kinetic theory of matter. This theory asserts that all matter is composed of small particles that are constantly in motion. For gases, the particles are incredibly far apart compared to the size of the particles themselves.
These gas particles are in constant and random motion and they move in straight lines until they collide with either another gas particle or the walls of their container.
Gases exert pressure on the walls of their container. This pressure is caused by the constant collisions of the gas particles with the walls.
Increasing the volume of the container while keeping the temperature constant will reduce the pressure exerted by the gas. This is because the gas particles have more space to move around and thus, there are fewer collisions with the walls. This relationship is defined by Boyle’s Law.
Similarly, reducing the volume of the container while keeping the temperature constant will increase the pressure exerted. The particles are now in a smaller space, leading to more collisions with the container walls.
The relationship between pressure and temperature for a fixed volume of gas is described by Charles’ law. This law states that the pressure exerted by a fixed quantity of gas is directly proportional to its absolute temperature. This means that if we increase the temperature, the pressure exerted by the gas also increases, and vice versa, provided that the volume remains constant.
Increasing the temperature of a gas leads to an increase in the kinetic energy of the gas particles. Hence, the particles move more rapidly and collide more often and with more force, causing the pressure to increase.
The relationships between pressure, volume, and temperature for a fixed amount of gas are summarised by the Ideal Gas law which states that the pressure of a gas multiplied by its volume is directly proportional to the absolute temperature of the gas.
Note that the kinetic theory and laws discussed here apply only to ideal gases. Real gases, under specific conditions, may not adhere to these laws strictly. But for your level of study, these laws form the fundamental understanding of the behaviour of gases.

Review these points and try to explain them in your own words to ensure you have internalised their meanings. Apply these laws to different examples to effectively reinforce your understanding.