Absolute Zero (Edexcel IGCSE Physics (Modular))

Absolute zero

• The amount of pressure that a gas exerts on its container is dependent on the temperature of the gas

  • This is because particles move with more energy as their temperature increases

• As the temperature of the gas decreases, the pressure on the container also decreases

• In 1848, mathematician and physicist, Lord Kelvin, recognised that there must be a temperature at which the particles in a gas exert no pressure

  • At this temperature they must no longer be moving, and hence not colliding with their container

• This temperature is called absolute zero and is equal to −273 °C

At absolute zero, or −273 °C, particles will have no net movement. It is therefore not possible to have a lower temperature

• Absolute zero is defined as:

The temperature at which the molecules in a substance have zero kinetic energy 

• This means for a system at absolute zero, it is not possible to remove any more energy from it

• Even in space, the temperature is roughly 2.7 K above absolute zero

The Kelvin scale

• The Kelvin temperature scale begins at absolute zero

  • 0 K is equal to -273 °C 

  • An increase of 1 K is the same change as an increase of 1 °C

• It is not possible to have a temperature lower than 0 K

• This means a temperature in Kelvin will never be a negative value

• To convert between temperatures θ in the Celsius scale, and T in the Kelvin scale, use the following conversion:

θ / ^°C = T / K − 273

T / K = θ / ^°C + 273

Conversion chart relating the temperature on the Kelvin and Celsius scales

• The divisions on both scales are equal. This means:

A change in a temperature of 1 K is equal to a change in temperature of 1 °C