Difference Between Ideal Gas and Real Gas

Ideal Gas vs Real Gas

Gas is one of the states in which matter exists. It has contradictory properties from solids and liquids. Gases do not have an order, and they occupy any given space. Their behavior is greatly affected by variables such as temperature, pressure, etc.

What is Ideal Gas?

Ideal gas is a theoretical concept, which we use for our study purposes. For a gas to be ideal, they should have following characteristics. If one of these is missing, then the gas is not considered as an ideal gas.

• Inter molecular forces between gas molecules are negligible.

• The gas molecules are considered as point particles. Therefore, compared to the space where the gas molecules occupy, molecules’ volumes are insignificant.

Normally gaseous molecules fill any given space. Therefore, when a large space is occupied by air, the gas molecule itself is very small compared to the space. Therefore, assuming gas molecules as point particles is correct to some extent. However, there are some gas molecules with a considerable volume. Ignoring the volume gives errors in these instances. According to the first assumption, we have to consider that there is no inter molecular interaction between gaseous molecules. However, in reality, there are at least weak interactions between those. But, gaseous molecules move quickly and randomly. Therefore, they don’t have enough time to make inter molecular interactions with other molecules. Therefore, when look in this angle, it is somewhat valid to accept the first assumption also. Although we say ideal gases are theoretical, we can’t say it is 100% true. There are some occasions where gases act as ideal gases. An ideal gas is characterized by three variables, pressure, volume and temperature. Following equation defines ideal gases.


P= absolute pressure

V= volume

n= number of moles

N= number of molecules

R= universal gas constant

T= absolute temperature

K= Boltzmann constant

Although there are limitations, we determine the behavior of gases using the above equation.

What is Real Gas?

When one of the two or both assumptions given above is invalid, that gases are known as real gases. We actually encounter real gases in the natural environment. A real gas varies from the ideal condition at very high pressures. This is because, when a very high pressure is applied, the volume where the gas is filled becomes very smaller. Then compared to the space we cannot ignore the size of the molecule. In addition, ideal gases come to the real state at very low temperatures. At low temperatures, kinetic energy of gaseous molecules is very low. Therefore, they move slowly. Because of this, there will be inter molecular interaction between gas molecules, which we cannot ignore. For real gases, we cannot use the above ideal gas equation because they behave differently. There are more complicated equations for the calculations of real gases.


What is the difference between Ideal and Real Gases?

• Ideal gases do not have intermolecular forces and the gas molecules considered as point particles. In contrast real gas molecules have a size and a volume. Further they have intermolecular forces.

• Ideal gases cannot be found in reality. But gases behave in this manner at certain temperatures and pressures.

• Gases tend to behave as real gases in high pressures and low temperatures. Real gases behave as ideal gases at low pressures and high temperatures.

• Ideal gases can be related to the PV=nRT=NkT equation, whereas real gases cannot. For determining real gases, there are much more complicated equations.