term "real gas" among chemists and physicists called such gases, the properties of which is directly dependent on their molecular interaction.Although in any specialized directories can read that one mole of these substances under normal conditions and steady state occupies a volume of approximately 22.41108 liters.This statement is true only in respect of the so-called "ideal" gases for which, according to the Clapeyron equation, do not act the forces of mutual attraction and repulsion of the molecules, and takes the last volume is negligibly small.
course, these substances do not exist, so all these arguments and calculations are purely theoretical orientation.But the real gases, which are to some extent deviates from the ideal, found all the time.Between the molecules of these substances are always forces of mutual attraction, which means that their value is somewhat different from the deduced perfect model.And all real gases have varying degrees of deviation from the ideal.
But here can be traced quite clear trend: the higher the boiling point of a substance close to zero degrees Celsius, the more the compound is different from the ideal model.The equation of state of a real gas, owned by the Dutch physicist Johannes Diederik van der Waals forces, they were withdrawn in 1873.In this formula, which has the form (p + n2a / V2) (V - nb) = nRT, introduced two very substantial amendments in comparison with the Clapeyron equation (pV = nRT), determined experimentally.The first one takes into account the forces of molecular interaction, which affects not only the type of gas, but also its volume, density and pressure.The second amendment is determined by the molecular weight of the substance.
most important role these adjustments becoming a high-pressure gas.For example, for nitrogen at 80 atmospheres indicator.calculations will be different from the ideal of about five per cent, and with increasing pressure to four atmospheres difference reached already hundred percent.It follows that the laws of the ideal gas model is very approximate.Retreat from them is both quantitative and qualitative.The first manifests itself in the fact that Clapeyron equation holds for all real gases is very approximate.Retreat is a qualitative character much deeper.
Real gases may well be converted into a liquid and, in the solid state of aggregation, which would be impossible in their strict adherence to the Clapeyron equation.Intermolecular forces on such materials lead to the formation of various chemical compounds.Again, this is impossible in the theoretical ideal gas system.The so-formed bonds are called chemical or valence.In the case where the real gas is ionized, it begin to appear Coulomb attractive forces that determine the behavior of, for example, plasma, which is a quasi neutral ionic species.This is especially true in light of the fact that plasma physics is now extensive, rapidly developing scientific discipline, which has an extremely wide application in astrophysics, the theory of radio wave signals, the problem of controlled nuclear and thermonuclear reactions.
chemical bonds in real gases by their nature do not differ from the molecular forces.And those and others in the long run reduce the electrical interaction between elementary charges, all of which built the atomic and molecular structure of matter.However, a complete understanding of the molecular and chemical forces made possible only with the emergence of quantum mechanics.
We have to admit that not every state of matter that is compatible with the equation of the Dutch physicist, can be implemented in practice.This requires also a factor of their thermodynamic stability.One of the important conditions for the stability of the substance is such that the pressure in the isothermal equation must be strictly observed tendency to reduce the total body.In other words, with increasing values of V all the isotherms of a real gas have been steadily falling.Meanwhile, in the isothermal plots Van der Waals forces below the critical level of temperature observed climbing areas.The points in these zones correspond to the unstable state of the substance, which in practice can not be realized.
