An ideal gas
is defined as one in which all collisions between atoms or molecules are perfectly elastic
and in which there are no intermolecular attractive forces
. An ideal gas can be visualized as a collection of perfectly hard spheres
which collide but which otherwise do not interact with each other. In reality, no real gases are like an ideal gas and therefore no real gases follow the ideal gas law or equation completely.
At temperatures near a gases boiling point, increases in pressure will cause condensation to take place and drastic decreases in volume. At very high pressures, the intermolecular forces of a gas are significant.
However, most gases are in approximate agreement at pressures and temperatures above their boiling point. The ideal gas law is utilized by engineers working with gases because it is simple to use and approximates real gas behavior.
In an ideal gas, molecules have no volume and do not interact. According to the ideal gas law, pressure varies linearly with temperature and quantity, and inversely with volume.
pV = nRT
p is the absolute pressure of the gas
n is the amount of substance
T is the absolute temperature
V is the volume
R is the ideal, or universal, gas constant, equal to the product of the Boltzmann constant and the Avogadro constant,
In this equation the symbol R is a constant called the universal gas constant that has the same value for all gases—namely, R=8.31 J/mol K. We can rewrite the previous equation in an alternative form, in terms of a constant called the Boltzmann constant k, which is defined as:
k = R / NA = [8.31 J/mol K] / [6.02 x 1023 mol-1] = 1.38 x 10-23 J/K