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The physical laws describing the behaviour ofgases under fixedpressure,volume, amount of gas, andabsolutetemperature conditions are calledgas laws. The basic gas laws were discovered by the end of the 18th century when scientists found out that relationships between pressure, volume and temperature of a sample of gas could be obtained which would hold to approximation for all gases. The combination of several empirical gas laws led to the development of theideal gas law.
The ideal gas law was later found to be consistent withatomic andkinetic theory.
In 1643, the Italian physicist and mathematician,Evangelista Torricelli, who for a few months had acted asGalileo Galilei's secretary, conducted a celebrated experiment in Florence.[1] He demonstrated that a column of mercury in an inverted tube can be supported by the pressure of air outside of the tube, with the creation of a small section of vacuum above the mercury.[2] This experiment essentially paved the way towards the invention of the barometer, as well as drawing the attention ofRobert Boyle, then a "skeptical" scientist working in England. Boyle was inspired by Torricelli's experiment to investigate how the elasticity of air responds to varying pressure, and he did this through a series of experiments with a setup reminiscent of that used by Torricelli.[3] Boyle published his results in 1662.
Later on, in 1676, the French physicistEdme Mariotte, independently arrived at the same conclusions of Boyle, while also noting some dependency of air volume on temperature.[4] However it took another century and a half for the development of thermometry and recognition of the absolute zero temperature scale, which eventually allowed the discovery of temperature-dependent gas laws.
In 1662, Robert Boyle systematically studied the relationship between the volume and pressure of a fixed amount of gas at a constant temperature. He observed that the volume of a given mass of a gas is inversely proportional to its pressure at a constant temperature.Boyle's law, published in 1662, states that, at a constant temperature, the product of the pressure and volume of a given mass of anideal gas in aclosed system is always constant. It can be verified experimentally using apressure gauge and a variable volume container. It can also be derived from thekinetic theory of gases: if a container, with a fixed number ofmolecules inside, is reduced in volume, more molecules will strike a given area of the sides of the container per unit time, causing a greater pressure.
Boyle's law states that:
The concept can be represented with these formulae:
whereP is the pressure,V is the volume of a gas, andk1 is the constant in this equation (and is not the same as the proportionality constants in the other equations).
Charles' law, or the law of volumes, was founded in 1787 byJacques Charles. It states that, for a givenmass of an ideal gas at constant pressure, the volume is directly proportional to itsabsolute temperature, assuming in a closed system.The statement of Charles' law is as follows:the volume (V) of a given mass of a gas, at constant pressure (P), is directly proportional to its temperature (T).
Charles' law states that:
Therefore,
where"V" is the volume of a gas,"T" is the absolute temperature andk2 is a proportionality constant (which is not the same as the proportionality constants in the other equations in this article).
Gay-Lussac's law, Amontons' law or the pressure law was founded byJoseph Louis Gay-Lussac in 1808.
Gay-Lussac's law states that:
Therefore,
,
Avogadro's law,Avogadro's hypothesis,Avogadro's principle orAvogadro-Ampère's hypothesis is an experimental gas law which was hypothesized byAmedeo Avogadro in 1811. It related the volume of a gas to theamount of substance of gas present.[5]
Avogadro's law states that:
This statement gives rise to themolar volume of a gas, which atSTP (273.15 K, 1 atm) is about 22.4 L. The relation is given by:
Thecombined gas law or general gas equation is obtained by combining Boyle's law, Charles's law, and Gay-Lussac's law. It shows the relationship between the pressure, volume, and temperature for a fixed mass of gas:
This can also be written as:
With the addition ofAvogadro's law, thecombined gas law develops into theideal gas law:
An equivalent formulation of this law is:
These equations are exact only for anideal gas, which neglects various intermolecular effects (seereal gas). However, the ideal gas law is a good approximation for most gases under moderate pressure and temperature.
This law has the following important consequences:
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