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Real Gas

Last updated date: 16th Apr 2024
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What Does Real Gas Refer To?

Usually, the word 'real gas' refers to a gas that does not function as an ideal gas. The interactions between gaseous molecules can explain their behaviour. Such intermolecular interactions between gas particles are the explanation of why the ideal gas law does not adhere to real gases. A real gas can therefore be characterized as a non-ideal gas whose molecules occupy a given amount of space and are capable of interacting with one another. In this article, we will study the real gas definition, real gas equation, and ideal and real gases in detail.


Real Gas Definition

A real gas is defined as a gas that at all standard pressure and temperature conditions does not obey gas laws. It deviates from its ideal behaviour as the gas becomes huge and voluminous. True gases have velocity, mass, and volume. They liquefy when cooled to their boiling point. The space filled by gas is not small when compared to the total volume of gas.


Ideal and Real Gas Equation

An ideal gas is defined as a gas that obeys gas laws at all pressure and temperature conditions. Ideal gases have velocity as well as mass. They have no volume. The volume taken up by the gas is small as compared to the overall volume of the gas. It does not condense and triple-point does not exist.


The ideal gas law is the equation of the state of a hypothetical ideal gas, also called the general gas equation. Under many conditions, it is a reasonable approximation of the behaviour of several gases, but it has many limitations. In 1834, Benoît Paul Émile Clapeyron first described it as a variation of the empirical law of Boyle, the law of Charles, the law of Avogadro, and the law of Gay-Lussac. In an empirical form, the ideal gas law is also written:




Real Gas Law

By explicitly including the effects of molecular size and intermolecular forces, the Dutch physicist Johannes van der Waals modified the ideal gas law to explain the behavior of real gases. The Van der Waal real gas equation is given below-


Real gas law equation,


= \[\frac {(P+an^2)} {V^2} = (V-nb) nRT\]


Where a and b represent the empirical constant which is unique for each gas.


\[\frac {n^2} {V^2}\] represents the concentration of gas. 


P represents pressure


R represents a universal gas constant and T is the temperature 


Ideal and Real Gases

The difference below shows the properties of real gas and ideal gas, and also the ideal and real gas behaviour.

Ideal Gas

Real Gas

No definite volume

Definite volume

Elastic Collision of particles

Non-elastic collisions between particles

No intermolecular attraction force

Intermolecular attraction force

Does not really exist in the environment and is a hypothetical gas

It really exists in the environment

High pressure

The pressure is less when compared to Ideal gas


Interacts with others

Obeys PV = NRT

Obeys \[P + ( \frac {(n^2a)} {V^2}) (V-nb) = nRT\]


Did You Know?

A factor known as compressibility factor Z is determined by the deviation of real gas from ideal gas and is defined as the ratio of the actual volume to the volume predicted by the ideal gas law at the same temperature and pressure Z = Actual volume/volume predicted by the ideal gas = v/RT/P     


But the ideal gas rate, Videal, is RT/P. The compressibility factor can therefore also be defined as the ratio of specific real gas volume to specific ideal gas volume, i.e.


Compressibility factor Z= \[\frac {V_{real gas}} {V_{ideal gas}}\]


As we all know, at very low pressures and high temperatures, all gases act as ideal gases. So when the pressures are reduced, as the gas behaves as ideal, the value of Z tends to unite. 


It is to be remembered that, depending on the pressure and temperature, the value of Z can be less than unity or greater than unity. The compressibility factor chart shows the Z values corresponding to the pressure.


Liquefaction of Gases

The kinetic molecular theory of gases does neither predict nor explain the liquefaction of gases. According to both theory and the ideal gas law, gases crushed to extremely high pressures and chilled to extremely low temperatures should still behave like gases, albeit cold, dense ones. When gases are compressed and cooled, they invariably condense to become liquids, although light elements like helium require extremely low temperatures to liquefy (for He, 4.2 K at 1 atm pressure).

Liquefaction can be thought of as an extreme deviation from ideal gas behavior. When the molecules in a gas are cooled to the point that their kinetic energy is no longer adequate to resist intermolecular attraction forces, this phenomenon happens. The exact temperature and pressure combination required to liquefy a gas is highly dependent on its molar mass and structure, with heavier and more complicated molecules liquefying at higher temperatures. Because large coefficients suggest relatively strong intermolecular attractive interactions, substances with large van der Waals coefficients are generally easy to liquefy. Small molecules containing only light components, on the other hand, have low coefficients, indicating weak intermolecular interactions and making them difficult to liquefy. On a large scale, gas liquefaction is used to separate O2, N2, Ar, Ne, Kr, and Xe. After liquefying a sample of air, the mixture is warmed, and the gases are separated according to their properties.

FAQs on Real Gas

1. What is an Example of a Real Gas?

Any gas that exists is a real gas. Oxygen, hydrogen, carbon dioxide, helium, carbon monoxide, etc. Real gases between particles have small attractive and repulsive forces and ideal gases do not. There is a volume of true gas particles and ideal gas particles do not.

2. What are the Assumptions of an Ideal Gas?

The ideal gas law assumes that gases behave ideally, meaning that they conform to the following characteristics: 

(1) the collisions between molecules are elastic and their motion is frictionless, meaning that the molecules do not lose energy.

(2) smaller magnitude is the total volume of the individual molecules.

3. What is Charle's Gas Law?

The physical concept known as Charle's law states that, as determined on the Kelvin scale, the volume of gas equals a constant value multiplied by its temperature (zero Kelvin corresponds to -273.15 degrees Celsius)

4.  What is Real gas?

A gas that does not act as an ideal gas is referred to as a "real gas." The interactions between the gaseous molecules help explain their behavior. Because of these intermolecular interactions between gas particles, real gases do not obey the ideal gas law.

Therefore, Real gases are non-ideal gases having molecules that take up a certain amount of space and may interact with one another.

5. What is an ideal gas?

An ideal gas is one that obeys the gas laws under all temperature and pressure conditions. To do so, the gas must follow the kinetic-molecular theory. The gas particles must have no volume and exhibit no attraction forces toward one another. There can be no such thing as a perfect gas since none of those requirements can be met. In reality, ideal gas does not exist. It is a hypothetical gas that has been proposed to make the computations easier.

6. What are the many factors that must be taken into account while dealing with real gases?

Several factors must be considered in order to comprehend how real gases behave. The many considerations that must be addressed while working with real gases are mentioned below.

  • Effects of compressibility on the real gas

  • Various real gases have different specific heat capacities.

  • Van der Waals forces have an effect on the interactions between molecules in a real gas.

  • The system's potential for non-equilibrium thermodynamic effects.

  • The gas's varied composition and changes in composition as a result of molecular dissociation, as well as any elementary processes that may occur.

7. What is the ideal gas equation?

We need a standard gas to study the properties of gases, but which gas should we use? There are thousands of different gases we might examine, including hydrogen, oxygen, helium, nitrogen, and carbon dioxide, to mention a few.

The researchers discovered that no matter what gas you analyze if you take a one-mole sample and put it in the same container at the same temperature, the pressure is nearly the same, and at lower densities, even those slight discrepancies in the readings vanish.

As a result, at extremely low densities, all actual gases tend to obey a single universal law known as the ideal gas law.

An equation known as the Ideal gas equation describes this law:

PV = nRT

8. Where can I find notes and questions on real gas and ideal gas?

Vedantu provides students with notes and questions on real gases and ideal gases.  This contains topics like the definition of real and ideal gases, as well as their characteristics and equations. Teachers who are specialists in their subjects create the content on Vedantu. Furthermore, the information is organized in such a way that students will have an easier time understanding and remembering the topics. Vedantu also provides students in grades 1 through 12 with study materials and a range of competitive exams. Notes, important topics and questions, revision notes, and other material are included in the material. All of these resources are available for free on Vedantu. Students must first register on the Vedantu website to access any of these resources. You may also use the Vedantu smartphone app to sign up.