Temperature (Edexcel IGCSE Physics (Modular))

Temperature & speed

• Imagine molecules of gas that are free to move around in a box

• The molecules in the gas move around randomly at high speeds, colliding with surfaces and exerting pressure upon them

• The temperature of a gas is a measure of the average speed of the molecules:

  • the higher the temperature of the gas, the faster the molecules move

  • This is because they have a greater average speed

Gas molecules move about randomly at high speeds

Temperature & kinetic energy

• Heating a system will change the energy stored in a system by increasing the kinetic energy of its particles

  • The Kelvin temperature of the gas is related to the average kinetic energy of the molecules

• This increase in kinetic energy (and therefore energy stored in the system) can:

  • Cause the temperature of the system to increase

  • Or, produce a change of state (solid to liquid or liquid to gas)

• The internal energy of a gas is the sum of the kinetic energy of all the molecules

• The higher the temperature, the higher the average kinetic energy of the molecules and vice versa

  • This means they move around faster

As the container is heated up, the gas molecules move faster with higher kinetic energy. The energy stored within the system - the internal energy - therefore increases

• If the temperature of a gas is increased, the particles move faster and gain kinetic energy

  • Therefore, they will collide more with each other and the container,, leading to an increase in pressure

• The temperature (in Kelvin) is proportional to the average kinetic energy of the molecules

T ∝ KE