Avogadro's Law

The principle, which in 1811 was formulated by the Italian chemist Amadeo Avogadro (1776-1856), says: for identical temperatures and pressures in equal volumes of gases, the same number of molecules will be contained, regardless of their chemical nature and physical properties. This number is a physical constant numerically equal to the number of molecules, atoms, electrons of ions or other particles contained in one mole. Later Avogadro's hypothesis, confirmed by a large number of experiments, began to be considered for ideal gases as one of the main laws that entered the science called Avogadro's law, and its consequences are all based on the assertion that the mole of any gas, in the case of identical conditions, will occupy the same volume, Called the molar one.

Amadeo Avogadro himself assumed that the physical constant is a very large quantity, but only a number of independent methods, after the death of the scientist, allowed to establish experimentally the number of atoms contained in 12 g (is the atomic unit of mass of carbon) or in the molar volume of gas (at T = 273.15 K and p = 101.32 kPa), equal to 22.41 liters. The constant is usually denoted as NA or less often L. It is named after the scientist - Avogadro's number, and it equals approximately 6.022 • 1023. This is the number of molecules of any gas in the volume of 22.41 liters, it is the same for light Gases (hydrogen), and for heavy gases (carbon dioxide). Avogadro's law can be mathematically expressed: V / n = VM, where:

• V is the volume of the gas;
• N is the amount of a substance that is the ratio of the mass of the substance to its mass molar;
• VM - constant of proportionality or molar volume.

Amadeo Avogadro belonged to a noble family, who lived in northern Italy. He was born on 08/09/1776 in Turin. His father, Filippo Avogadro, was an employee of the judicial department. The surname in the Venetian medieval dialect meant a lawyer or official who interacted with people. By the existing in those days, traditions, positions and professions were inherited. Therefore, in 20 years, Amadeo Avogadro received a degree, becoming a doctor of jurisprudence (church). Physics and mathematics, he began to study independently in 25 years. In his scientific work he was engaged in the study of electrical phenomena and research in the field of electrochemistry. However, Avogadro entered the history of science, making a very important addition to atomistic theory: he introduced the notion of the smallest particle of a substance (molecule) that can exist independently. This was important for explaining the simple volumetric relations between the gases that reacted, and Avogadro's law became of great importance for the development of science and widely used in practice.

But this did not happen immediately. Some chemists Avogadro's law was recognized in decades. The opponents of the Italian physics professor were such well-known and recognized scientific authorities as Berzelius, Dalton, Davy. Their misconceptions led to years of controversy about the chemical formula of the water molecule, since it was believed that it should be written not by H2O, but by HO or H2O2. And only Avogadro's law helped to establish the composition of water molecules and other simple and complex substances. Amadeo Avogadro claimed that the molecules of simple elements consist of two atoms: O2, H2, Cl2, N2. From which it follows that the reaction between hydrogen and chlorine, as a result of which hydrogen chloride will be formed, can be written in the form: Cl2 + H2 → 2HCl. When one Cl2 molecule interacts with one H2 molecule, two HCl molecules are formed. The volume that will occupy HCl must be twice as large as the volume of each of the components that entered into this reaction, that is, it should equal their total volume. Only since 1860, Avogadro's law began to be actively applied, and the consequences of it allowed us to establish the true values of the atomic masses of some chemical elements.

One of the main conclusions drawn on its basis was the equation describing the state of an ideal gas: p • VM = R • T, where:

• VM is the molar volume;
• P is the gas pressure;
• T is the absolute temperature, K;
• R is the universal gas constant.

The combined gas law is also a consequence of Avogadro's law. For a constant mass of a substance, it looks like (p • V) / T = n • R = const, and its recording form: (p1 • V1) / T1 = (p2 • V2) / T2 allows you to make calculations for gas transition from one state (Denoted by index 1) to another (with index 2).

Avogadro's law made it possible to draw a second important conclusion, which opened the way for an experimental determination of the molecular masses of those substances that do not decompose upon transition to the gaseous state. M1 = M2 • D1, where:

• M1 - molar mass for the first gas;
• M2 - molar mass for the second gas;
• D1 is the relative density of the first gas, which is set in hydrogen or air (hydrogen: D1 = M1 / 2, air D1 = M1 / 29, where 2 and 29 are molar masses of hydrogen and air, respectively).