Pressure and temperature

If the volume of a container with a gas inside stays the same, the pressure of a gas increases as its temperature increases.

The temperature of a gas is a measure of the average kinetic energy of its particles – the higher the temperature, the higher the average kinetic energy.

When hotter, the gas particles will be travelling faster and will collide with the walls of the container more frequently and with more force.

Graph of pressure against temperature. The line starts at 0 degrees C and three units of pressure, rising steadily to six units of pressure at 100 degrees C.

This means that there is a relationship between pressure and temperature. If a pressure gauge is connected to a flask of air and the flask is heated, a graph of pressure against temperature can be produced.

Kelvin temperatures

As the temperature of a gas increases, the pressure increases, showing a linear relationship between the two. If the temperature axis is rescaled, the graph shows that pressure is directly proportional to temperature.

The rescaling needed is to put the zero on the temperature scale at -273 °C. This is an alternative temperature scale called the Kelvin (or 'absolute') scale of temperature. This new zero of temperature is called absolute zero. At absolute zero, the average kinetic energy of the particles is zero and they stop moving.

Each degree Celsius is the same size as one kelvin. Raising the temperature by one degree Celsius also increases the value on the kelvin temperature scale by one.

TemperatureCelsius scaleKelvin scale
Boiling water100°C373 K
Freezing water0°C273 K
Absolute zero-273°C0 K
Typical room temperature20°C293 K
  • To convert °C into K, add 273.
  • To convert K into °C, subtract 273.