The molecular and kinetic theory which explains properties of substances on the basis of several postulates enters new definition – "ideal gas". Any gas which satisfies to these postulates is ideal. Strictly speaking, any gas existing in the nature is not ideal. However such abstraction helps to simplify a concept of the processes happening in gaseous substances.
Definition of ideal gas
Ideal gas is theoretical generalization which is used by physics for the analysis of probability theory. Ideal gas consists of molecules which make a start from each other and do not interact with vessel walls. In ideal gas there is no force of an attraction or pushing away between molecules, and energy is not lost during collisions. Ideal gas can be described completely by means of several parameters: volume, density and temperature.
The state equation for ideal gas, widely known as the Law on ideal gas, has an appearance:
PV = NkT. In the equation of N is a number of molecules, k – Boltzmann's constant which is equal about 14000 Joules on Calvin. The most important is that pressure and volume in inverse proportion each other, and in direct ratio to temperature. It means that if pressure increases twice, and temperature will not change, then gas volume will also double. If the volume of gas increases twice, and pressure will remain to constants, then temperature will double. In most cases, the number of molecules in gas is considered constant. Collisions between molecules of gas are not ideally elastic and a part of energy is lost. Also between molecules of gas there are electrostatic forces of interaction. But for the majority of situations the law of ideal gas is as close as possible to real behavior of gases. The ratio formula between pressure, volume and temperature can help the scientist to understand behavior of gas intuitively.
Practical application
The law of ideal gas is the first equation with which pupils get acquainted when studying gases at lessons of physics or chemistry. Van der Waals's equation which includes several insignificant corrections in the main assumptions of the law on ideal gas also is a component of many introduction courses. In practice these distinctions are so small that if the law of ideal gas is inapplicable for this specific case, then and Van der Waals's equation will not meet accuracy conditions. As well as in the majority of sections of thermodynamics, ideal gas also initially is in equilibrium state. This assumption is not true if pressure, the volume or temperature change. When these variables change gradually, such state, is called quasistatic balance and the mistake in calculations can be small. In a case when parameters of a system change chaotically, the model of ideal gas is inapplicable.