Difference Between Ideal Gas and Real Gas

The air that surrounds us, the animals that are around us, and even our own bodies are made up of molecules and various gases. These gases are an essential part of our lives. We breathe and emit gases every second.

But there are distinct kinds of gases. Some are even hypothetical. The difference between Ideal gas and Real gas helps us understand gases in a better way.

Ideal Gas vs Real Gas

The main difference between Ideal gas and Real gas is that the former is a hypothetical gas, whereas the latter exists in real-time. Ideal gas always obeys the laws of gas, while real gas obeys those laws under certain conditions. The two gases also differ in terms of the volume their molecules occupy, the way they interact, etc.

Ideal Gas vs Real Gas

Ideal Gas is a theoretical gas, which means it does not exist in reality. It obeys the gas laws at all conditions of pressure and temperature. An ideal gas has multiple minute particles that randomly move in all directions as they are not subject to interparticle interaction.

On the other hand, Real gas is present in the environment around us. Real gases obey gas laws only at conditions of high temperature and low pressure. The molecules of these gases interact with each other, which is why they do not behave like an ideal gas.

Comparison Table Between Ideal Gas and Real Gas

Parameters of ComparisonIdeal GasReal Gas
DefinitionAn ideal gas follows all the gas laws under all conditions of pressure and temperature.Real gases only follow the gas laws under conditions where the pressure is low and the temperature is high.
Movement of MoleculesThe molecules in an ideal gas are free to move and do not participate in interparticle interaction.The molecules of a real gas collide with each other and are subject to interparticle interaction.
Volume OccupiedThe volume occupied by an ideal gas is negligible in comparison to the total volume.The volume occupied by a real gas is substantial when compared to the total volume.
PressureAn ideal gas has high pressure.The actual pressure in a real gas is lower than the pressure of an ideal gas.
Forces presentNo intermolecular forces of attraction are present in an ideal gas.The forces present in a real gas are either attractive or repulsive.
FormulaAn ideal gas follows the formula; PV=nRTReal gases obey the formula, (P+(an2/V2))(V-nb)=nRT.

What is Ideal Gas?

Composed of multiple particles that move randomly in all directions, the Ideal gas is the one that is not subject to interparticle interaction.

It obeys the gas laws, as well as the equation of state. In an ideal gas, the collisions between molecules are perfectly elastic; this means that there is no loss of kinetic energy when a collision occurs. 

 An ideal gas does not have any intermolecular forces of attraction. It is a hypothetical gas which means that it does not exist in the environment. The model of an ideal gas law has been explored in both Newtonian Dynamics as well as in quantum mechanics.

 It can be theoretically understood that an ideal gas that it arises from the kinetic pressure of gas molecules. The molecules collide with the walls of a container by following the laws of Newton.

It is also understood that when the pressure of an ideal gas is reduced in a throttling process, there will be no change observed in its temperature.

An ideal gas does not condense as it has a negligible volume. It also lacks a triple point, which is a point at which the temperature and pressure of solid, liquid, and gaseous phases of a pure substance can coexist in equilibrium. An ideal gas obeys the formula PV=nRT.

ideal gas

What is Real Gas?

Real gases are those gases that follow the gas laws under certain conditions. They are not the ideal gases. For real gases to exist, the pressure should be low, and the temperature should be high.

The gaseous particles of real gases move and interact with each other. These collisions are inelastic, which means that there is some loss of kinetic energy.

The molecules of real gases occupy volume. Intermolecular forces in a real gas could be either attractive or repulsive. A real gas is not hypothetical, which means it exists in the atmosphere.

There are multiple models for explaining the equation of state of a real gas but the most often used is Van Der Waal’s model.

The volume of a real gas remains considerably high at high pressure as compared to an ideal gas. Also, when the pressure of a real gas is reduced in a throttling process, the temperature is likely to either increase or decrease depending upon whether Joule-Thompson is positive or negative.

As opposed to Ideal gas, a real gas would condense when it is cooled to its boiling point. The common examples of real gases include Oxygen, Nitrogen, Hydrogen, Carbon dioxide, etc. The formula obeyed by a Real Gas is (P+(an2/V2))(V-nb)=nRT.

real gas

Main Differences Between Ideal Gas and Real Gas

  1. An ideal gas is a hypothetical gas, whereas Real gas exists in the nature around us.
  2. Ideal gas obeys the gas laws, and on the other hand, Real gases obey the gas laws in conditions of low pressure and high temperature.
  3. Ideal gas does not undergo condensation, while Real gases undergo condensation when cooled up to their boiling point.
  4. An ideal gas has a negligible volume as compared to the total volume, whereas a real gas has a significantly higher volume as compared to the ideal gas.
  5. Ideal gas does not exist, whereas the examples of Real Gas include Oxygen, Hydrogen, Carbon dioxide, etc.
  6. There are no intermolecular forces present in an ideal gas. Contrarily, the intermolecular forces in a real gas could be either repulsive or attractive.


An ideal gas is one wherein the collisions between all molecules are elastic in nature, which means they are not subject to interparticle interaction. An ideal gas does not exist in reality.

It is purely theoretical in nature. The concept of ideal gas helps us understand the gas laws as well as analyze statistical mechanics.

A real gas is one that, in conditions of standard pressure and temperature, does not obey the gas laws.

Its molecules interact with each other, and therefore the real does not behave like an ideal gas. A real gas has velocity, mass, and volume. They tend to liquefy when cooled to their boiling points.


  1. https://asmedigitalcollection.asme.org/GT/proceedings-abstract/GT1969/V001T01A071/231855
  2. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.73.922
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