go to homepage

Perfect gas

Chemistry and physics
Alternative Title: ideal gas

Perfect gas, also called ideal gas, a gas that conforms, in physical behaviour, to a particular, idealized relation between pressure, volume, and temperature called the 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 general 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 to the volume occupied by the gas; and (3) no forces act on the molecules except during elastic collisions of negligible duration.

Although no gas has these properties, the behaviour of real gases is described quite closely by the general 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.

Read More
gas (state of matter): Ideal gas

The general 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 = 8.314472 joules per mole-kelvin.

Learn More in these related articles:

heated air expands
one of the three fundamental states of matter, with distinctly different properties from the liquid and solid states.
Embryonic stars in the Eagle Nebula (M16, NGC 6611)This detail of a composite of three images taken by the Hubble Space Telescope shows a section populated by new stars forming from molecular hydrogen in the nebula.
...take account of the change in the star’s structure with time as its hydrogen supply is gradually converted into helium. Fortunately, given that most stars can be said to be examples of an “ideal gas” (see perfect gas), the relations between temperature, density, and pressure have a basic simplicity.
Figure 1: Phase diagram of argon.
In an ideal gas—where there are no forces between molecules, and the volume of the molecules is negligible—g is unity, which means that the chance of encountering a second molecule when moving away from a central molecule is independent of position. In a solid, g takes on discrete values at distances that correspond to the locations associated with the solid’s crystal...
perfect gas
  • MLA
  • APA
  • Harvard
  • Chicago
You have successfully emailed this.
Error when sending the email. Try again later.
Edit Mode
Perfect gas
Chemistry and physics
Tips For Editing




Leave Edit Mode

You are about to leave edit mode.


Thank You for Your Contribution!



Uh Oh


Email this page