Combined Gas Law is a gas law which is a combination of the Boyle’s Law, Gay-Lussac’s Law and Charles’s Law. The law is considered as a consequence of these three laws. Interrelation of these variables can be seen in Combined Gas Law that states that ratio between pressure-volume product and temperature of systems remains constant. Using this gas law helps to mathematically predict the consequences of change in temperature, volume and pressure. The law can also be used in explaining mechanics where temperature, volume and pressure are affected.

There is no official founder for this law; it is merely an amalgamation of the three previously discovered laws. These laws each relate one thermodynamic variable to another mathematically while holding everything else constant. Charles’s law states that volume and temperature are directly proportional to each other as long as pressure is held constant. Boyle’s law asserts that pressure and volume are inversely proportional to each other at fixed temperature. Finally, Gay-Lussac’s law introduces a direct proportionality between temperature and pressure as long as it is at a constant volume. The inter-dependence of these variables is shown in the combined gas law, which clearly states that:

The ratio between the pressure-volume product and the temperature of a system remains constant.

This can be stated mathematically as:



P is the pressure
V is the volume
T is the temperature measured in kelvin
k is a constant (with units of energy divided by temperature).

For comparing the same substance under two different sets of conditions, the law can be written as:


The addition of Avogadro’s law to the combined gas law yields the ideal gas law.

Combined Gas Law uses the relationships share by temperature, pressure and volume which are the variables found in Boyle’s Law, Gay-Lussac’s Law and Charles’s Law. This is considered as an amalgamation of these three previously occurring laws as no official founder is known for this law. Boyle’s law states that volume and pressure, at a fixed temperature, are inversely proportional to each other. Gay-Lussac’s law affirms the proportionality between pressure and temperature till it is at constant volume. Finally, the Charles’s law states that temperature and volume are directly proportional to each other until the pressure is kept constant.


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