*3.3.1. Gases*

is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles [33, 34]. The number of specified structural elements in one mole of a substance is called Avogadro constant (Avogadro's number), usually denoted as NA. Thus, the carbon-12 of mass 0,012 kg contains NA atoms. Physical value "amount of substance" should not be called a "number of moles", as it is impossible to name the physical

The current definition of the mole depends on the definition of the kilogram. The XXIV [22] adopted a resolution [22] which had proposed to re-define a mole as a category. Mol should remain a unit of amount of substance; but its value will be determined not by the fixed mass 0,012 kg of carbon-12, but by the numerical value of the Avogadro constant. On the opinion of *Bureau International des Poids et Mesures, BIPM*, «Redefining the mole so that it is linked to +an exact numerical value of the Avogadro constant *N*<sup>A</sup> would have the consequence that it is no longer dependent on the definition of the kilogram even when the kilogram is defined so that it is linked to an exact numerical value of *h*. This would thereby emphasize the distinction

Indeed, mass is a physical characteristic of matter, which expresses and simultaneously measures the gravitational and inertial properties of the matter. The amount of matter is the number of atoms, molecules, ions and other structural units that build the matter. One value of the mass of a substance can correspond to a series of numerical values of quantities of the substance. For example, the mass of the Universe is constant, but the amount of matter in it can be calculated differently if its structure is considered as a set of Galaxies, star systems, molecules and atoms, protons and electrons, photons or other atomic particles. The difference between mass and amount of a substance can serve as the physical basis of the existence in Nature of the right of choice. The bearer of this right is the man as a part of the Universe. The

When building a system of units derived from number of substances the first values should be the values that are expressed only through the basic units of the system. The diagram below

> Mass, m Amount of the substance, ν Mole mass, M = m/ ν Specific amount of substance, ν / m

Density, *ρ* = m/ V ?

substance to its volume. The equation determining σ is as follows:

Specific volume, v = V/ m Mole volume, Vmol = V / ν

This scheme shows that its logical completion needs entering another derived value. This may be the density of the amount of substance, which is proposed to be denoted by symbol σ.

The density of substance quantity σ is a physical value equal to ratio of the amount of a

size of the "mass" as "the number of pounds" or "number of kilograms" [12].

between the quantities "amount of substance" and "mass"» [4].

observer in the theory of relativity proofs it.

illustrates this requirement.

110 Solar Cells - New Approaches and Reviews

**3.2. Velues derived from amount and mass of substance**

Molecule can be accepted a a structural element of gas. Table 1 lists values of densities of amount of substance σ for some matters calculated according to eq. (2). Density of amount of substance for gaseous simple matters under normal conditions does not depend on chemical nature of gas and is equal 44.6 mole molecules/m<sup>3</sup> . Gas of molecules of chemical compounds has the same value of σ. The Avogadro law says that all gases in the same states have a constant value of σ. The ratio ν/σ for any matters is equal to the volume of substance and does not depend on the choice of structural element.

The number of molecules determines the volume ratios of gases; the number of atoms determines weight ratios. Therefore, the density of gaseous matters has fundamentally different functional dependences: the ratio ρ / σ is equal to the mass of a mole of a substance and depends on choice of structural element, chemical nature and it is proportional to the ordinal number of the element.
