Ideal gas | Definition, Equation, Properties, & Facts (2024)

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Also known as: perfect gas

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ideal gas, a gas that conforms, in physical behaviour, to a particular idealized relation between pressure, volume, and temperature called the ideal, or general, gas law. This law is a generalization containing both Boyle’s law and Charles’s law as special cases and states that for a specified quantity of gas, the product of the volume V and pressure P is proportional to the absolute temperature T; i.e., in equation form, PV = kT, in which k is a constant. Such a relation for a substance is called its equation of state and is sufficient to describe its gross behaviour.

The ideal gas law can be derived from the kinetic theory of gases and relies on the assumptions that (1) the gas consists of a large number of molecules, which are in random motion and obey Newton’s laws of motion, (2) the volume of the molecules is negligibly small compared with the volume occupied by the gas, and (3) no forces act on the molecules except during elastic collisions of negligible duration.

More From Britannicagas: Ideal gas

Although no gas has these properties, the behaviour of real gases is described quite closely by the ideal gas law at sufficiently high temperatures and low pressures, when relatively large distances between molecules and their high speeds overcome any interaction. A gas does not obey the equation when conditions are such that the gas, or any of the component gases in a mixture, is near its condensation point, the temperature at which it liquefies.

The ideal gas law may be written in a form applicable to any gas, according to Avogadro’s law, if the constant specifying the quantity of gas is expressed in terms of the number of molecules of gas. This is done by using as the mass unit the gram-mole; i.e., the molecular weight expressed in grams. The equation of state of n gram-moles of a perfect gas can then be written as PV/T = nR, in which R is called the universal gas constant. This constant has been measured for various gases under nearly ideal conditions of high temperatures and low pressures, and it is found to have the same value for all gases: R = 8.314462 joules per mole-kelvin.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Erik Gregersen.

Ideal gas | Definition, Equation, Properties, & Facts (2024)

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Ideal gas | Definition, Equation, Properties, & Facts? ›

In such a case, all gases obey an equation of state known as the ideal gas law: PV = nR

R
The dimensions of the universal gas constant R are energy per degree per mole. In the metre-kilogram-second system, the value of R is 8.31446261815324 joules per kelvin (K) per mole. The universal gas constant is defined as Avogadro's number NA times the Boltzmann constant k.
https://www.britannica.com › science › universal-gas-constant
T, where n is the number of moles of the gas and R is the universal (or perfect) gas constant, 8.31446261815324 joules per kelvin per mole.

What is ideal gas and its properties? ›

The properties of IDEAL gases are that: they are compressible. they are always in motion, colliding elastically within a container. they take the shape of the container. they behave inertly.

What is ideal gas and its equation? ›

The ideal gas equation is formulated as: PV = nRT. In this equation, P refers to the pressure of the ideal gas, V is the volume of the ideal gas, n is the total amount of ideal gas that is measured in terms of moles, R is the universal gas constant, and T is the temperature.

What is the equation relating the properties of an ideal gas? ›

The ideal gas law can also be written and solved in terms of the number of moles of gas: PV = nRT, where n is number of moles and R is the universal gas constant, R = 8.31 J/mol ⋅ K.

What does the ideal gas law describe? ›

noun. , Physics. the law that the product of the pressure and the volume of one gram molecule of an ideal gas is equal to the product of the absolute temperature of the gas and the universal gas constant.

What are the 5 characteristics of an ideal gas? ›

Principles of Ideal Gas

The molecules of the gas are always in motion. The distance present between the two molecules is only slightly larger than the individual molecule size. The molecule has only kinetic energy and not potential energy. The collisions that take place between the molecules are elastic.

What describes an ideal gas? ›

The term ideal gas refers to a hypothetical gas composed of molecules which follow a few rules: Ideal gas molecules do not attract or repel each other. The only interaction between ideal gas molecules would be an elastic collision upon impact with each other or an elastic collision with the walls of the container.

Why is it called the ideal gas equation? ›

The gases which strictly follow the general equation (PV=nRT) are called ideal or perfect gases. Actually, there is no gas which is perfect or ideal. A real gas is one which actually exists, whether it obeys gas laws strictly or not.

What are the conditions for an ideal gas? ›

For gas to be “ideal” there are four governing assumptions: The gas particles have negligible volume. The gas particles are equally sized and do not have intermolecular forces (attraction or repulsion) with other gas particles. The gas particles have perfect elastic collisions with no energy loss.

How is ideal gas different from real gas? ›

An ideal gas's particles lack a fixed volume and mass. A real gas's particles have a defined volume and mass. Ideal gas particles have constant kinetic energy. Collisions change the kinetic energy of real gas particles.

What makes a gas less ideal? ›

In summary, a real gas deviates most from an ideal gas at low temperatures and high pressures. Gases are most ideal at high temperature and low pressure.

How is the ideal gas law used in everyday life? ›

Ideal Gas law has a lot more practical applications. It is being used to determine the densities of gases and in stoichiometric calculations. The coolants/refrigerants in your refrigerator, hot air balloons in the sky, and combustion engines in vehicles, all are based on the ideal gas law.

What is the behavior of an ideal gas? ›

Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure, as the potential energy due to intermolecular forces becomes less significant compared with the particles' kinetic energy, and the size of the molecules becomes less significant compared to the empty space between them.

What is the ideal gas equation and explain the terms? ›

In such a case, all gases obey an equation of state known as the ideal gas law: PV = nRT, where n is the number of moles of the gas and R is the universal (or perfect) gas constant, 8.31446261815324 joules per kelvin per mole.

What are the 5 assumptions of an ideal gas? ›

The five main postulates of the KMT are as follows: (1) the particles in a gas are in constant, random motion, (2) the combined volume of the particles is negligible, (3) the particles exert no forces on one another, (4) any collisions between the particles are completely elastic, and (5) the average kinetic energy of ...

What is the application of the ideal gas equation? ›

Meteorologists use the ideal gas law to calculate air pressure at different altitudes in the atmosphere. By knowing the temperature, volume, and number of gas molecules in a particular air mass, they can determine the pressure exerted by that air mass. This helps in predicting weather.

What are the properties of an ideal gas mixture? ›

Ideal Gas Mixtures

When the gases have the same temperature, their molecules have the same average kinetic energy. Thus, each gas obeys the ideal gas law separately and exerts the same pressure on the walls of a container that it would if it were alone.

What are the properties of an ideal solution? ›

Ans: n ideal solution has the following characteristics: (i) mixing volume change should be zero. (ii) mixing heat change should be zero.

What is ideal gas and real gas explain? ›

Ideal gas is a hypothetical gas which follows the Ideal Gas Law at all conditions of temperature and pressure. All gases which exist in the environment are Real Gases. Real gases follow Ideal Gas Law only under conditions of high temperature and low pressure. So, ideal gas is not a real gas!

What is an ideal gas or perfect gas explain? ›

A perfect gas (ideal gas) is a gas that obeys the ideal gas law fully in its physical behavior. It connects the pressure of the gas, the amount of space occupied by the gas number of gas molecules, as well as the absolute temperature of the gas.

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