Writing Chemical Equations

A balanced chemical equation is a way of showing the relationships between the reactants (the starting materials) and the products (the resulting substances) involved in a chemical reaction. The equation shows the chemical formulae of the reactants and products, and the number of atoms of each element that are present in each substance.

It’s important to use state symbols when writing balanced chemical equations. State symbols give the reader an idea of the state of the substance, whether it is a solid, liquid, gas, or aqueous solution. We write the state symbols in brackets after each chemical formula, which you can see in the table below.

StateState symbol
Aqueous solution(aq)

Word Equations

Chemical reactions can be complex and hard to understand. But with word equations, we can simplify and make sense of them. A word equation represents a chemical reaction using the full chemical names of the substances involved.

In a word equation, the reactants are written on the left-hand side of the arrow and the products are on the right-hand side.

Reactants Products

The arrow represents a chemical or physical transformation that takes place, converting the reactants into products. If there are two or more reactants or two or more products, they are separated by a plus sign. If a catalyst is involved in the reaction, its name can be written above the arrow.

Below is an example of a word equation:

Copper sulfate + MagnesiumCopper + Magnesium sulfate

In this example, the reactants are:

  • Copper sulfate
  • Magnesium

And the products are:

  • Copper
  • Magnesium sulfate

Symbol equations

We can also write chemical equations using chemical symbols for each reactant and product. This is known as a chemical symbol equation.

A chemical symbol equation shows the atoms involved in the reaction on both sides of the equation. For example:

C + O2  CO2

The equation shows that a carbon atom (C) is reacting with an oxygen molecule (O2) to form carbon dioxide (CO2).

Another example is:

N2 + 3H2 2NH3

In this equation, a nitrogen molecule (N2) is reacting with three hydrogen molecules (H2) to form two molecules of ammonia (NH3).

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