Combined Science Physics P3 - The Particle Model and Motion in Gases

You can explain the way that matter behaves in terms of how its particles move and the forces between them. 

The three states of matter are solid, liquid and  gas.

The particles of a substance in each state are the same - only the arrangement and energy of the particles are different.

• Strong forces of attraction hold the particles together in a fixed, regular arrangement.
• The particles don't have much energy so they can only vibrate about in their fixed positions

• There are weaker forces of attraction between the particles
• The particles are close together, but can move past each other and form irregular arrangements. 
• They have more energy than the particles in a solid
• They move in random directions at low speeds

• There are almost no forces of attraction between the particles
• The particles have more energy than in liquids and solids
• The particles are free to move
• The particles are constantly moving with random directions and speeds

• Particles in gases are free to move around. As they move, they bang into each other and anything else around them
• When they collide with something, they exert a force onto it
• (Pressure = the force exerted per unit area)
• In a sealed container, the outward gas pressure is the total force exerted by all of the particles in the gas on a unit area of the container walls

• If you increase the temperature of a gas, you transfer energy into the kinetic energy stores of its particles
• The temperature of a gas is related to the average energy in the kinetic energy stores of the particles in the gas
• The higher the temperature, the higher the average energy
• So, as you increase the temperature of a gas, the average speed of its particles increases
• The energy in the particles kinetic energy stores = 1/2mv^2

This means that, for a gas at a constant volume, increasing its temperature would increase its pressure:

• As the particles are travelling quicker, it means they hit the sides of the container more often in a certain amount of time
• Each particle also has a larger momentum which means that they exert a larger force when they collide with the container

These factors both increase the total force exerted on a unit area, and so increase the pressure