Chemical equation

A chemical equation is a special way to show what happens during a chemical reaction. It uses symbols and chemical formulas to tell us which substances change and what new substances are made.

The things that start the reaction, called reactants, are written on the left side. The new substances made, called products, are written on the right side. A plus sign is used between each substance, and an arrow points to the products to show the reaction is moving forward.

Chemical equations can look simple or very detailed. Numbers called coefficients in front of the symbols tell us exactly how many parts of each substance are involved.

The very first chemical equation was drawn by a person named Jean Beguin in 1615. Since then, chemical equations have become an important tool for scientists.

Structure

A chemical equation shows a chemical reaction. It lists the substances you start with, called reactants, on the left, and the substances made, called products, on the right. An arrow points from the reactants to the products.

Each substance is shown by its chemical formula. Sometimes a number is placed before the formula. This number tells how many parts of that substance are in the reaction. If no number is shown, it means there is one part.

For example, the reaction between hydrochloric acid and sodium can be written as:

2HCl + 2Na → 2NaCl + H₂

This means two parts hydrochloric acid and two parts sodium make two parts sodium chloride and one part hydrogen gas.

→ {\displaystyle \rightarrow }	net forward reaction
⇄ {\displaystyle \rightleftarrows }	reaction in both directions
⇌ {\displaystyle \rightleftharpoons }	equilibrium
= {\displaystyle =}	stoichiometric relation
↔ {\displaystyle \leftrightarrow }	resonance (not a reaction)

Balancing chemical equations

Main article: Stoichiometry

In a chemical reaction, the same amount of each element must be on both sides of the equation. This means the number of atoms of each element must match. When this happens, the equation is balanced.

To balance an equation, we change the numbers in front of each chemical. Simple equations can be balanced by trying different numbers until they match.

Balanced equations usually use the smallest whole numbers. For example, the reaction to make lithium fluoride:

Li (s) + ½ F₂ (g) ⟶ LiF (s)

As seen from the equation CH4 + 2 O2 → CO2 + 2 H2O, a coefficient of 2 must be placed before the oxygen gas on the reactants side and before the water on the products side in order for, as per the law of conservation of mass, the quantity of each element does not change during the reaction

Inspection method

The inspection method means looking at the equation and adjusting the numbers step by step. We start with the most complex chemical and set its number to 1. Then we adjust the other numbers so both sides have the same atoms.

For example, balancing the combustion of methane:

CH₄ + 2O₂ ⟶ CO₂ + 2H₂O

We start with 1 CH₄. This gives us 1 carbon atom and 4 hydrogen atoms. To balance carbon, we need 1 CO₂. To balance hydrogen, we need 2 H₂O. Finally, to balance oxygen, we need 2 O₂.

System of linear equations

P4O10 + 6 H2O → 4 H3PO4This chemical equation is being balanced by first multiplying H3PO4 by four to match the number of P atoms, and then multiplying H2O by six to match the numbers of H and O atoms.

We can also use math to balance equations. Solving these equations gives the right numbers for each chemical.

Matrix method

Another math method uses matrices. Solving this matrix equation gives the balanced equation.

For the methane example, the matrix method also gives:

CH₄ + 2O₂ ⟶ CO₂ + 2H₂O

This shows how math can help balance chemical equations.

Ionic equations

An ionic equation shows a chemical reaction where substances are written as separate ions. This is used for reactions that happen in water, like when two liquids mix and form a solid.

For example, when calcium chloride mixes with silver nitrate, a solid forms. In the ionic equation, some ions stay the same on both sides and do not change. These are called spectator ions. By removing these, we get a simpler net ionic equation that shows only the parts that actually react. In acid and base reactions, the net ionic equation often shows hydrogen ions and hydroxide ions forming water.

History

The idea of using symbols to show chemical reactions started a long time ago. Early scientists found ways to write down what happens when substances mix and change. Over time, these ideas grew into the way we write chemical equations today, helping us understand chemistry better.

Typesetting

A chemical equation shows what happens in a chemical reaction using symbols and formulas. The things that start the reaction, called reactants, are written on the left side. The things made in the reaction, called products, are written on the right side. A plus sign separates each reactant and product, and an arrow points to the products to show the reaction is moving forward. These formulas can be simple symbols, pictures of structures, or a mix of both.