Lesson 2: The Variables of a Gas

• Experiments on the expansion of a gas with heat are not simple because a gas changes its volume if the pressure, the temperature or both change.
• (For solids and liquids this difficulty does not arise: their compressibility is very small.)

To study a gas we have to consider three variables — volume (V), pressure (P) and temperature (T) — and do three separate experiments, in each of which the relationship between two variables is studied while the third is held constant (and the mass of the gas is fixed):