What is Ideal Gas Equation

What is Ideal Gas?

An ideal gas is a theoretical gas made up of a set of randomly-moving point particles that interact only through elastic collisions. The perfect gas principle works because it follows the ideal gas law, a simplified equation of state, and is open to analysis under statistical mechanics.

Ideal Gas Laws

The laws which deal with ideal gases are naturally called ideal gas laws and the laws are identified by the observational work of Boyle in the seventeenth century and Charles in the eighteenth century.

Boyles Law– states that for a given mass of gas held at a constant temperature, the gas pressure is inversely proportional to the gas volume.

Charles Law– states that for a given fixed mass of gas held at a constant pressure the gas volume is directly proportional to the gas temperature.

Ideal Gas Equation

The Ideal gas equation is the formula for the state of a theoretical ideal gas. It is a great approximation to the behaviour of lots of gases under numerous conditions, although it has a number of several limitations. The ideal gas equation can be written as

PV = n RT

Formulation of Ideal Gas Equation

While describing Boyle’s and Charles’s laws, some of the variables are held continuous throughout the changes produced in the gases. According to Boyle’s law.

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According to Charles’s law.

V T (when n and P are held constant).

It is a well-known fact that volume of the provided gas at constant temperature level and pressure is directly proportional to the number of moles (Avogadro’s law).

V n (when P and T are held constant).

If we think for a moment that none of the variables are to be kept constant then all the above 3 relationships can be joined together.


The consistent suggested is R which is called the general gas constant.


The equation is called an ideal gas equation. It is likewise referred to as the general gas equation. This formula shows that if we have any quantity of an ideal gas then the product of its pressure and volume is equal to the product of number of moles, general gas constant, and absolute temperature. This equation is decreased to Boyle’s law, Charles’s law and Avogadro’s law, when appropriate variables are held constant.

PV = n RT, when T and n are held constant, PV = k (Boyle’s law).

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Ideal Gas Constant R

The values and units of R can be determined by Avogadro’s principle really easily. Its value depends on the systems chosen for pressure, volume and temperature level. The volume of one mole of an ideal gas at STP (one atmospheric pressure and 273.16 K) is 22.414 dm3. Putting these values in the general gas equation will provide the value of R.


When the pressure is in atmospheres, volume in dm3, then the value of R, used needs to be 0.0821 dm3 atm K-1 mol-1.

The physical significances of this value are that, if we have one mole of an ideal gas at 273.16 K and one atmospheric pressure and its temperature is increased by 1 K, then it will take in 0.0821 dm3 -atm of energy, dm3 -atm is the system of energy in this circumstance. Thus, the value of R is a universal parameter for all the gases. It informs us that Avogadro’s number of molecules of all the perfect gases have the same demand of energy.

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