Main Concept

The three gas laws that laid the foundation for the ideal gas law are as follows:

Boyle's law: At constant temperature, the volume of a gas is inversely proportional to its pressure.

Charles's law: At constant pressure, the volume of a gas is proportional to the absolute temperature.

Gay-Lussac's law: At constant volume, the pressure of a gas is proportional to its temperature.

The combined gas law combines these laws and summarizes the relationship between thermodynamic variables (volume $V$, pressure $p$, and absolute temperature $T$):

$\frac{p_1{V}_1}{T_1}\=\frac{p_{2 }{V}_2}{T_2}$.

Note that the temperature is absolute, so it must be expressed in Kelvin (K) as opposed to Celsius ($°$C) or Fahrenheit ($°$F) for the equation to hold numerically. Typically, experiments are conducted at standard pressure and temperature, 101.3 kPa and 25°C. It is important to note that sometimes volume, pressure and temperature are expressed in terms of non-standard units. The following table contains conversions to SI units:

Initial Conditions

Final Conditions

 Pressure:

Pressure: 101.3 kPa

 Temperature:

Temperature: 25°C (298 K)

 Volume:

Volume: ?

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