Chemical equation

A chemical equation is the symbolic description of a chemical reaction (that is, how a chemical process of nature is represented in written form, by means of symbols). It shows the substances that react (called reactants) and the substances that are produced (called products). The chemical equation helps to more easily visualize the reactants and products. In addition, you can locate the chemical symbols of each of the elements or compounds that are within the equation and be able to balance them more easily.

In 1615 Jean Begin published Tyrocinium Chymicum, one of the first written works on chemistry, in which he wrote the first chemical equation in history.

Requirements for a chemical equation

A chemical equation must satisfy a series of laws, simultaneously:

• Comply with the law of conservation of matter.
• Comply with the law on the maintenance of the load.
• Compliance with the Energy Conservation Act.

Note that it is not specified that the process in question actually occurs in nature or in the laboratory. For example, the overall chemical equation for the formation of gaseous water from the substances dihydrogen and dioxygen (presented below) actually occurs in a series of intermediate steps (called reaction mechanisms), corresponding to the sequence of chemical reactions that occur to produce the given product.

Interpretation of a chemical equation

A general case of a chemical equation would be:

aA+bB→ → cC+dD{displaystyle a,mathrm {A} +b,mathrm {B} to c,mathrm {C} +d,mathrm {D} }

where:

• A, B, C, D, represent the chemical symbols or the molecular formula of the atoms or molecules that react (left side) and those that occur (right side).
• a, b, c, d, represent the schiometric coefficients, which must be adjusted directly to the law of mass conservation.

The physical interpretation of the stoichiometric coefficients, if these are whole and positive numbers, can be in atoms or moles. Thus, one would say the stoichiometric equation of geometry is subdivided into the following:

• When "a" molecules of A react with "b" molecules of B produce "c" molecules of C, and "d" molecules of D.
• When "a" moles of A molecules react with "b" moles of B molecules produce "c" moles of C molecules, and "d" moles of D molecules.

For example dihydrogen gas (H₂) can react with dioxygen (O₂) to give water in phase (thermodynamics) gas (H₂O). The chemical equation for this reaction is written:

H2+O2→ → H2O{displaystyle mathrm {H} _{2}+mathrm {O} _{2}to mathrm {H} _{2}mathrm {O} }

The symbol + is read as “reacts with”, while the symbol → is read as “produces”. To adjust the proposed equation (enforce the law of conservation of matter), we put the stoichiometric coefficients:

2H2+O2→ → 2H2O{displaystyle 2,mathrm {H} _{2}+mathrm {O} _{2}to 2,mathrm {H} _{2}mathrm {O} } }

The equation is balanced and can be interpreted as 2 mol of dihydrogen molecules react with 1 mol of dioxygen molecules, producing 2 mol of water molecules.

Chemical formulas to the left of the reaction arrow (→) represent the reactants or reactants; To the right of the reaction arrow are the chemical formulas of the substances produced, called the products.

The numbers in front of the formulas are called stoichiometric coefficients. These must be such so that the chemical equation is balanced, that is, that the number of atoms of each element of the reactants and of the products of the reaction is the same. The coefficients must be positive integers, and the one is omitted. In the only reactions that this does not occur is in nuclear reactions.

Finally (but not least), the molecular aggregation states of each participating substance must be added (between parentheses and as a subscript): solid (s), liquid (l), watery (aq) or gaseous (g).

In the water example:

2H2(g)+O2(g)→ → 2H2O(l){displaystyle 2,mathrm {H} _{2(g)}+mathrm {O} _{2(g)}to 2mathrm {H} _{2}mathrm {O} _{(l)}}}}