2 Chemical equations

Chemical equations are representations of chemical reactions.

At this point you do have some experience of the use of numbers and symbols to represent elements and compounds (chemical formulas), chemical equations use these as a starting point.

Let’s begin by writing an equation for a simple reaction, one which is crucial to our everyday lives; the combustion of natural gas in air. Natural gas is almost pure methane whose molecules are made up of carbon and hydrogen atoms (i.e. it is hydrocarbon). And, methane burns in (reacts with) oxygen to yield the molecules carbon dioxide and water along with the production of heat.

In writing a chemical equation to represent this process, the first step is to identify the reactants and the products.

The reactants are written on the left and the products on the right to give, initially, a word ‘equation’:

Even this simple word equation carries a lot of useful information in a relatively concise form, but you can go further. You know already that a formula reveals much more about a particular substance than does a name.

The molecular formula of methane is CH₄.

So the next step is to replace the names of the compounds in the equation with appropriate formulas.

So now you could write:

The word and can be replaced by the plus sign, +, and the reaction representation becomes:

Even at this early stage of development of the equation, there is useful information about the chemistry going on.

It is important to note that the relationship provides information about the overall reaction. It does not say anything about how the reaction actually occurs, such as the way in which bonds are broken and formed to give the final products. Essentially it provides a summary of the reaction.