Matter: Particle Motion in Gases

Properties of Gases

Gases are made up of tiny particles which are in constant, random motion.
The particles have lots of space between them which means gases are free to expand and fill their containers.
Unlike solids and liquids, gases are highly compressible. This is because gas particles can move easily and freely in all directions.

Kinetic Theory is used to explain the properties of gases. According to this theory, the properties of gases can be explained by the constant, random motion of their particles.
Particles in a gas move in straight lines until they hit something and change direction in a random way.
When gas particles collide with each other, or with the walls of their container, there is no loss of kinetic energy. This is known as an elastic collision.
The temperature of a gas is directly proportional to the average kinetic energy of its particles. This means that when the temperature of a gas increases, the kinetic energy of the particles also increases, leading to faster particle motion and more frequent collisions.

Pressure is force exerted per unit area. In the context of gases, pressure is caused by gas particles colliding with the walls of their container.
The pressure exerted by a gas is directly proportional to its temperature. This is because as the temperature increases, the speed of the particles also increases, causing them to collide with the walls of the container more frequently and with greater force.
Conversely, increasing the volume of the container while keeping the number of particles and temperature constant would decrease the pressure; this is due to less frequent collisions with the walls of the container caused by the increased space.

The particle motion in gases as described by the kinetic theory is what differentiates gases from liquids and solids in terms of their physical states.
In a solid, the particles are tightly packed and vibrate about fixed positions, while in a liquid, the particles are loosely packed and move about to a greater extent. In a gas, the particles move with high speed in all directions due to the ample space available.
Changes in temperature and pressure can trigger state changes. For instance, increasing the temperature of a solid can cause it to melt into a liquid, and then evaporate into a gas.