Real gases are any gases that do not obey the ideal gas law - specifically for the applications that you mention they are gases with compressibility factors (pV/RT) different than 1. The non-ideal properties of gases become more important as (a) pressure increases, (b) temperature decreases, or (c) conditions approach the critical point. The widely published compressibility chart shows how temperature and pressure affect the compressibility factor and how every gas can become a real (non-ideal) gas under some pressure and temperature conditions.

Real gases are any gases that do not obey the ideal gas law - specifically for the applications that you mention they are gases with compressibility factors (pV/RT) different than 1. The non-ideal properties of gases become more important as (a) pressure increases, (b) temperature decreases, or (c) conditions approach the critical point. The widely published compressibility chart shows how temperature and pressure affect the compressibility factor and how every gas can become a real (non-ideal) gas under some pressure and temperature conditions.

I do agree with Dear Larry L. Baxter for his good and clear answer. I may add atmospheric air (and other gases) under moderate conditions usually we treat them as ideal gases. There is a physical definition of an ideal gas related to the interact forces between molecules. For more specific definition you may refer to a physics text book.

Any gas in nature may be called a "real" gas. Ideal gases are those can be described by PV/RT or so close to it that the deviation can be omitted. All gases can be called real gases at some specific conditions, but not all real gases can be called ideal gases according to their physical or chemical properties. Some of them may just not fall into this category in their phase behavior.

Thank you Larry L. Baxter, Elhadi I. Dekam and Lian Cheng Wang for providing good useful answers. Further, any technical additions or discussions on real gases are invited.

Explanation part for real gas is well documented. I am adding the application part of real gas.

Consider a real gas like Supercritical carbon dioxide (S-CO2). Near critical point, it require less compression work in relative to generic fluids. So on using S-CO2 in compressor we can improve efficiency. Further, the higher density of S-CO2 add a further advantage of compactness.

Another case of real gas is in rocket nozzle, fuel is at high temperature and high pressure; hence it become no longer obey ideal gas law. Any numerical calculations should consider this real gas effect. There comes the great "Dr. Van der Waals"

Thank you Senthil Kumar Raman for providing the useful answer.

Ideal gases are one which follows or obeys gas laws. Whereas real gas does not obey gas laws. vander Waals equation is used for real gases.

Ideal gases follows follows gas laws whereas real gases follows vander Waals equation of state. All the general equations are for ideal gases.

All of us know that all gases are real but not ideal. All gases are treated to be ideal only when they are at zero pressure. At this stage all of them follow gas laws.

The gases existing are all real gases and there are no ideal gases. Real gases come closer to ideal gases at zero pressure. There is no perfect ideal gas but to have air, steam are considered to be perfect or ideal gases where all gas laws can be applied.

All are real gases. There is no ideal gas. A gas is considered real when specific heats both at constant pressure and constant volume varies with temperature continously.

All gases known are all real. Real gases properties vary much and ideal gas equations cannot be applied. All the gases behaves ideal at zero pressure and high temperature.

Real gases are gases existing or got every where in nature. Nature consists of several gases and the evaluation of their behaviour in a particular equipment are considered under ideal conditions. Calculation of values of real gases are valid to ideal gases only on the assumption that specific heat at constant pressure and specific heat at constant volume taken a constant value with change in temperature.

All gases are real and available in nature. Air is taken to be ideal gas, since it is in thermodynamic equilibrium. Real gases does not follow the gas laws since specific heats vary continuously with temperature.

Real gases like carbon dioxide, ammonia, chloro flouro carbons etc find application to use as refrigerants, generation of these gases will be from internet combustion engines, industries etc.

Ideal gases obey the ideal gas law pV=nRT. The compressibility factor Z = pV/RT is unity for an ideal gas. When higher pressures are encountered the gas behaves more like a real gas rather than an ideal gas. Z factor graphs are available to assess the departure from ideal gas behavior and use it in real situations such as a chemical reactor that needs high pressure reactants to form a product or in turbines. See for example http://www.che.ncku.edu.tw/FacultyWeb/ChenBH/E340100%20Thermodynamics/Supplementary/Compressibility_factor%20Nov%202011.pdf for such diagrams.

Thank you Srini Vasan for your answer.

All gases are real gases. This has application as refrigerants, as a fuel in internal combustion engines etc.

The real gas in chemistry, physics and mechanical engineering, is a gas characterized by qualities that can not be treated by the ideal gas law, and real gas is not an ideal gas. It is a gas that constantly confronts us in our working life where engines operate and affect the weather.

Thank you Afraa Ibrahim for your answer.

I agree with the Dr. Larry L. Baxter

• A real gas is a gas that does not behave as an ideal gas due to interactions between gas molecules.
• Any gas that exists is a real gas. Nitrogen, oxygen, carbon dioxide, carbon monoxide, helium etc. ...
• Real gases have small attractive and repulsive forces between particles and ideal gases do not.
• Real gas particles have a volume and ideal gas particles do not.

Real Gas Example

While cool air at ordinary pressure behaves like an ideal gas, increasing its pressure or temperature increases the interactions between molecules, resulting in real gas behavior that cannot be predicted reliably using the ideal gas law.

Thank you Wafaa Alhashemi and Devi Parameswari C for your answers.

On earth all are real gases except air treated to be ideal gas. Real gas like nitrogen is used to pump air in tyres. Carbon dioxide gas is sprayed to reduce fire. Burning of hydro carbon fuel which gives gases in turn are real gases.

All the gases available are real gases. These are used for several purposes like carbon dioxide is used for stopping fire, ammonia is used as refrigerant, hydrogen is used as a fuel etc.

All the gases used on the earth are real gases. Real gases use vander Waal's equation to solve for properties of gas. Real gas like monohloro difluoro methane (Freon - 22) is used as refrigerant, compressed natural gas (CNG) is used as fuel and butane can be used as gas for cooking.

A gas said to be real when there are variations of specific heats. All the gases are not perfect or ideal except air. Hydrogen balloons in parties and functions, Oxygen cylinders for fresh air and butane gas cylinders for house hold are some of real gas applications.

Real gases are gases which do not follow ideal gas laws. Except air and steam all are real gases. The application will be pumping gas into tyres (nitrogen), refrigerants iused in refrigerantors and air conditioners (sulphur dioxide, carbon dioxide, ammonia, Freon-12) and cooking gas (butane).

https://opentextbc.ca/introductorychemistry/chapter/real-gases-2/

All gases existing on earth are real gases. Air and pure steam are taken to be perfect gases which obeys ideal gas laws. Real gases follow Vander Waals' equation since specific heats of these gases are not constant and is variable with temperature. Nitrogen is used to fill gas in automobile tyres and carbon dioxide is used for stopping fire.