The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Chemical Equation

a statement of a chemical reaction in the form of chemical signs, chemical formulas, numbers, and mathematical signs. Although the possibility of such statements on the basis of the law of conservation of mass was suggested by A. Lavoisier in 1789, chemical equations came into general use only in the first half of the 19th century.

A chemical equation consists of a left side and a right side joined together by an equal-sign. Sometimes, the symbol → is used in place of an equal-sign in order to indicate the direction of a reaction, with double arrows (⇄) used in the case of reversible reactions. The formulas for the reactants are written on the left side, and those for the products are written on the right; + signs are placed between the formulas on each side of the equation.

In writing chemical equations, the mass of the products must be equal to that of the reactants, and the number of atoms of any given element must be the same on both sides of the equation. Coefficients, which must be whole numbers, are placed in front of the formulas for the reactants and products. For example, knowing that water and carbon dioxide are formed from the combustion of methane in oxygen, the chemical equation for this reaction may be written immediately:

(1) CH₄ + 2O₂ = 2H₂O + CO₂

In more complicated cases, other methods are used, such as those for redox reactions (seeOXIDATION-REDUCTION REACTION) and those based on the solution of systems of indeterminate equations. For example, assume that the coefficients in the chemical equation for the roasting of pyrite (FeS₂) in oxygen are sought:

(2) xFeS₂ + yO₂= zFe₂O₃ + tSO₂

It is obvious that x = 2z, t = 2x, and 2y = 3z + 2t. Letting z = 1, we have x = 2, t = 4, and y = 5.5. Multiplying these numbers by 2, we obtain

4FeS₂ + 11O₂ = 2Fe₂O₃ + 8SO₂

Chemical equations serve as a basis for calculations required in the laboratory and in industry.

REFERENCE

Nekrasov, B. V. Osnovy obshchei khimii, 3rd ed., vol. 1. Moscow, 1973.

S. A. POGODIN

Mentioned in

References in periodicals archive

Students to predict the macroscopic changes that they would expect, given the balanced chemical equation for the above reaction.

Facilitating high school students' use of multiple representations to describe and explain simple chemical reactions

But suddenly, the Play Doh has been replaced by plaster of Paris for an A-level art sculpture, currently occupying half the kitchen, picture books by metaphysical poetry, and the laptop is jammed with chemical equations I'll never hope to comprehend.

Summertime, and the livin' isn't easy with exams nigh

This general chemistry textbook introduces the structure of an atom, the periodic table, ionic and covalent bonds, chemical equations, phases of matter, solutions, chemical reaction concepts, acid-base chemistry, and basic nuclear chemistry.

General, Organic, and Biological Chemistry, 7th Edition

"Relationships are like chemical equations," psychology expert Kerolos Bahgat said.

Self-esteem, ego and upbringing: a triple threat to relationships

At a press conference, Ryabkov pointed out that those proofs do not have any political purpose, adding, "They are numbers, signs and conclusions in the form of chemical equations." He noted that the Syrian government handed these proofs to the head of the UN investigation mission Ake Sellstrom before he left Syria.

President al-Assad to Ryabkov: Russia's support to Syria inspires hope of drawing new map for global balance

In that sense, the fall or collapse of any government becomes a mere passing event, because it is not linked to the collapse of a tendency or the end of a movement, rather to chemical equations in which many parties are involved.

Morocco: Loyalists and Opposition

"I can't get up there with a bunch of chemical equations and formulas and all that kind of stuff," he said.

As experiment, science pubs a huge success

Chapters cover the fundamental principles of the scientific method; measurement units and how to apply them properly, especially when converting units or solving problems; atomic structure; elements and compounds; the shapes of molecules; chemical equations; thermochemistry; and more.

The Science Shelf

Students should already have some experience with the following: (1) Understanding and reading the pH scale; (2) Knowledge of the carbon cycle; (3) Using scientific notation to express large and small values; and (4) Reading chemical equations. This curriculum incorporates a scaled approach to learning.

Understanding Ocean Acidification

Use fermentation ([C.sub.6][H.sub.12][O.sub.6] = [2C.sub.2][H.sub.5]OH + [2CO.sub.2]) to balance chemical equations. Teaching physics?

Why interpret beer?

The biological reactions that take place during the treatment of wastewater by microorganisms can be described by chemical equations where organic matter is converted by action of microorganisms with oxygen to carbon dioxide, water, new cells, and other by-products (Metcalf and Eddy, 1991).

Modeling of an industrial wastewater treatment system using historical process data