What are Gas Laws?

Gas laws describe the ways in which volume, temperature, pressure, and other conditions correlate when matter is in a gaseous state. The very first observations about the physical properties of gases was made by Robert Boyle in 1662. Later discoveries were made by Charles, Gay-Lussac, Avogadro, and others. Eventually, these observations were combined to produce the ideal gas law.

Physical Properties of Gaseous State

• Gases are highly compressible in nature.
• Pressure exerted by gases is equal in all directions.
• Density of gases is lower than solids and liquids.
• The shape and volume of gases are not fixed but vary depending on the shape of the container.
• Without any action of mechanical force, gas can be completely mixed in even proportion. 

Boyle’s Law

Robert Boyle performed an experiment on the basis that he reached a conclusion that, at a constant temperature the pressure of a particular amount (i.e. number of moles to be n) of gases is inversely proportional with its volume. 

This equation states that if a gas has a certain fixed amount then in that case at constant temperature T occupying volume V1 at pressure p1 undergoes expansion, by this process volume becomes V2 and pressure becomes p2.

Graphical Representation of Boyle’s Law

According to Boyle’s law p is inversely related to V.

So, the graphical representation between p versus 1/V will be:

Charles's Law

This law states that in a closed system constant pressure, volume of gas is in direct relation with temperature (in Kelvin). These gas laws describe a direct relationship between the temperature and volume of the gas, which means with decrease in temperature will lead to decrease in volume.

This law is applicable only on ideal gas which is kept at constant pressure but their temperature and volume keep on changing with time.

Graphical Representation of Charles Law

In this gas law, graph is plotted between volume (V) and Temperature (T) at constant pressure which is known as isobar. While plotting this graph, a straight line is obtained.

Application of Charles Law in Real Life

• Helium balloons shrink in cold weather or cold environments.
• Lung capacity decreases in winter when the weather is cold, which can make exercise more difficult for athletes.

Gay-Lussac's Law

This law establishes a relationship between temperature and pressure at constant volume. Under this law it is stated that at a constant volume, the pressure of the given gas is in direct relation to the temperature for a given gas.

When one heat up the gas, molecules receives more energy and because of this they start moving faster. Whereas, if cooled down the gas there molecules slow down which decreases the pressure.

Graphical Representation of Gay-Lussac Law

Below is the graph which explains the relationship between pressure and absolute temperature of a gas.

The given relationship between pressure and temperature is identified from Boyle’s law and Charles’ Law. The straight line in this graph is called isochore.

Avogadro's Law

Italian scientist Amedeo Avogadro combined two different laws i.e. Dalton atomic theory and Gay Lussac’s law of combining volumes during his experiment. Later from these two different laws he formulated Avogadro law. This law states that when volumes of all gases are equal if kept under the similar given temperature and pressure, then they contain equal numbers of molecules. Or it can also be said that at similar given temperature and pressure, the volume is dependent on the number One mole of glasses has 6.022×10² number of molecules. This number is known as Avogadro constant.

 As we know that volume of gas is in direct relation with the number of moles; under STP i.e., under the condition of standard temperature and pressure one mole of each gas will have the same volume. Value of standard temperature is 273.15 K i.e. 0⁰C whereas standard pressure is 1 bar i.e. 105 Pascal pressure. This standard value is approximately equal to the freezing point of water and seal level atmospheric pressure.

• An ideal gas molar volume STP i.e. standard temperature pressure is equal to 22.71098 mol^-1.
• Molar volume of an ideal gas at STP is 22.71098 L mol^–1.

Ideal Gas Law

By combining all three gas laws a combined law is made which is termed as the ideal gas equation. It is a hypothetical gas law.

As Boyle's law states, pressure is inversely proportional to volume. Charles's law states that volume is in direct relation with temperature and by combining these two laws Ideal gas law is formed.

Mathematical equation for Ideal gas equation that has been formulated by taking all the equations into account:

$\mathrm{PV}=\mathrm{nRT}$

Where

• P = pressure of the ideal gas
• V = volume of the ideal gas
• n = amount of ideal gas measured in moles
• R = universal gas constant and its value is 8.314 J.K-1mol-1
• T = temperature

 Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for Bachelors and Masters in chemistry.

Related Concepts

• States of matter
• Kinetic theory
• Liquefaction of gases