# Pressure law

The pressure law states that pressure is proportional to temperature, for a fixed amount of gas at constant volume.

Key Concepts

$$p\propto T$$

• $$p$$ is pressure (Pa)
• $$T$$ is temperature (K)

$${p_1\over T_1}={p_2\over T_2}$$

The pressure law is the basis of the Kelvin scale. When gas molecules stop moving, the pressure becomes zero as there are no collisions with the walls. The temperature on the Kelvin scale falls to absolute zero, the lowest temperature possible, as there is no kinetic energy.

Essentials

Simulated experiment

The pressure law can be verified by measuring the pressure of a gas at different temperatures.

Kinetic theory explanation

Comparing two equal volumes of gas, we can see that the pressure of the hot one is greater than the cold. This is because the molecules hit the walls harder due to their increased kinetic energy.

Test Yourself

Use quizzes to practise application of theory.