Chemical reactions: Chemical equations

Here's some graphite powder - a form of carbon, made entirely of carbon atoms. The air contains a lot of oxygen gas, made of - oxygen atoms. If we set the graphite on fire... ... we will get a chemical reaction between the two substances. The carbon atoms and the oxygen atoms are still there, but now they are attached to each other.

They have formed a new substance - carbon dioxide. There are several different ways to describe this chemical reaction. One simple description is just to say what substances we started with, and what substances we end up with. In this example, we started out with carbon and oxygen gas, and ended up with carbon dioxide. Writing it like this: "Carbon plus oxygen, arrow, carbon dioxide," is called a word equation.

It looks a bit like a mathematical equation, but instead of an 'equals' sign, we write an arrow. The arrow is called a reaction arrow, and shows the direction of the reaction. The substances we start with - the substances that react - are called reactants. The substances that are formed are called products. Another way to represent this chemical reaction, is to draw the atoms, and how they are connected.

The carbon atoms are bonded together in billions, forming large crystals. But we only need to draw one of the carbon atoms to show the reaction. The atoms in oxygen gas are attached two by two, forming oxygen molecules. We can draw them like this. The atoms in carbon dioxide also form molecules, with one carbon atom in the middle, and two oxygen atoms, one on each side.

The name carbon-DI-oxide shows that there are two oxygen atoms in the molecule, since "DI" means two. Inside the atoms, we can write the shortened name for each kind of atom, the chemical symbols. Carbon is written as C, Oxygen is O. Sometimes, we just show the chemical symbols, without drawing the atoms around them. This way of showing what molecules look like is called a structural formula.

A third way to depict the reaction, is to use the abbreviation for each substance - its chemical formula. The carbon atom are still written as a single C, but the substances that form molecules are written in a specific way. The atoms in oxygen gas, that are attached two by two, are written like this: O-two. The number is written after the atom that there is more than one of. The product formed, carbon dioxide, contains one carbon atom and two oxygen atoms: C - O - two.

Therefore, the whole reaction looks like this: C plus O-two Reaction arrow C - O - two. Describing a chemical reaction in this way, using chemical symbols, is called a chemical equation. So these are three ways to describe the chemical reaction between carbon and oxygen: ... Using a word equation, writing the names of the substances. ... Using the structural formulae of the substances, showing what their molecules look like.

Or, using a chemical equation, that shows the number of atoms of each kind.