Law of equivalents

In the Great Explanatory Dictionary, the equivalent word (in Latin sounds like aequivalens) is explained as something equivalent, equivalent or equivalent to another, that can completely replace it. In chemistry, the law of equivalents (used since the end of the 18th century, studied in the school, applied by chemists and biologists of different countries in theory and practice) establishes that all chemicals enter into reactions in quantities proportional to their equivalents. The law was opened by the German chemist IV Richter, whose works for a long time were unknown. In his three-volume work, published between 1792 and 1794 under the title "The Beginnings of Stoichiometry, or the Way of Measuring Chemical Elements," the scientist showed that the chemicals react in strict proportion. He also introduced a term such as "stoichiometry". Now this is a whole section of chemistry, which describes the ratio of reagents entering into chemical interaction.

Richter was the first in his works to cite quantitative reaction equations. They are a conditional entry containing qualitative and quantitative information about the processes occurring during the interaction of various chemicals called reagents. Even during the alchemical science, scientists used different symbols to denote simple elements; later, formulas of complex (consisting of several elements) chemicals were discovered. But only IV Richter (under the influence of his teacher and philosopher Immanuel Kant, who claimed that certain branches of the natural sciences contain as much true science as there are mathematicians in it) used in the thesis chemical formulas and the concept of "stoichiometry", described the quantitative equations of the reaction And discovered the Law of Equivalents. The formula expressing it can be written: E2 • m1 = E1 • m2. Where m1 and m2 are the masses of substances "1" and "2" that reacted, and E1 and E2 are their chemical equivalents.

To understand the Law of Equivalents, it is necessary to clarify that the equivalent is a conditional or real amount of a substance that can attach a hydrogen cation in acid-base reactions or an electron as a result of oxidation-reduction reactions. Equivalent mass is the mass of one equivalent. It is believed that 1 equivalent of the substance reacts (or displaces) with 1 gram of hydrogen or with 8 grams of oxygen, or 35.5 grams of chlorine. In practice, the amount of the substance in the equivalent often has a very small value, so it is customary to express it in moles. 1 mole contains a constant number of particles (atoms, ions or molecules), it is equal to the Avagadro number: NA = 6,02214179 (30) · 1023. The mass of one mole of substance, expressed in grams, is numerically equal to its mass in atomic units of mass.

Based on the Law of Equivalents, it can be argued that with acid-base titration proceeding according to the reaction equation: KOH + HCl → KCl + H2O, as a result of the interaction of 1 mole of potassium hydroxide with 1 mole of hydrochloric acid, 1 mole of salt, called potassium chloride, And 1 mole of water. That is, the equivalent mass of potassium hydroxide is equal to E KOH = 39 + 16 + 1 = 56 g, hydrochloric acid - E HCl = 1 + 35 = 36 g, potassium chloride - E KCl = 39 + 35 = 74 g, water - E H2O = 1 • 2 + 16 = 18 g. In order to completely neutralize 56 g of potassium hydroxide, 36 g of hydrochloric acid is necessary. The result is 74 g of potassium chloride and 18 g of water. But since it is established by law that the masses of substances that reacted are proportional to their equivalents, knowing the amount of one reagent, one can calculate how much the second reagent reacts or calculate the yield of the product.

For example, how much will potassium chloride be obtained if it is known that 100 g of potassium hydroxide has been completely neutralized by hydrochloric acid? Using the law of equivalents, we can write: 56 • mKCl = 74 • 100. Then mKCl = (74 • 100) / 56 = 132 g. A hydrochloric acid to neutralize 100 potassium hydroxide will require 64 g. If 100 g of potassium hydroxide is neutralized with sulfuric acid: 2KOH + H2SO4 → K2SO4 + 2H2O, this will require a completely different amount of acid. As indicated by the stoichiometric coefficients of this reaction, 1 mole of sulfuric acid reacts with 2 moles of potassium hydroxide, and as a result 1 mole of potassium sulfate and 2 moles of water will be obtained. Knowing that the masses of the reacted substances are proportional to equivalent masses, we can write: 2 • 56 • mH2SO4 = 98 • 100, then to neutralize 100 potassium hydroxide, mH2SO4 = 88 g sulfuric acid is required. In this case, 155 g of potassium sulfate are formed. The amount of water released as a result of neutralization of 100 g of potassium hydroxide by hydrochloric acid or sulfuric acid will be the same and equal to 32 g.

Applies the Law of Equivalents Chemistry (analytical, inorganic, organic, etc.) for the study of substances and other experiments based on the calculation of the balance of chemical reactions. In addition, it is used (for the compilation of material balances) in the design and operation of laboratory, pilot or industrial plants intended for the synthesis of chemicals. They are constantly used by specialists in chemical, medical, biological, sanitary and epidemiological laboratories, as it underlies the formulas used to calculate many test results.