Ways to represent chemical reactions

Flour, sugar, baking powder, cooking oil, and egg - that's what's needed to make a tasty cake. And of course, heat. it says how much to use of each ingredient. In the recipe, In much the same way, you can write the recipe for a chemical reaction. Take four hydrogen atoms -- they come two by two.

Add two oxygen atoms, which also come in pairs. Add heat, and voila You have water! We call the substances that react - reactants. And the results we call - products. But what if we want to show the reaction using something other than images?

Well, there's a special language used for chemical reactions. We use the symbol of the element. You might recognise these from the periodic table of elements. H for example, represents hydrogen O is oxygen C-L means chlorine And B-A is barium. Here we have two hydrogen atoms.

We write that as "2 H". But hydrogen atoms never come alone, without being attached to each other. So we represent them like this, with a subscript number: H-two. Now we need to show how many bits of each substance take part in the reaction. First there's two of the hydrogen molecules.

Then we add a plus sign -- that shows that other elements also take part in the reaction. We take one oxygen molecule. But we don't have to write the one. Then we show in which direction the reaction is going, with a... reaction arrow.

The result -- water -- we write as H-2-O. And then we show how many water molecules are formed. That is -- two. Now let's make it a bit more complicated. We let barium -- B-A -- react with Water -- H-2-O.

Then we get -- hydrogen gas -- and -- barium hydroxide. For each barium atom, we need twice the number of water molecules. Why is that? Because, in order to form a hydrogen molecule, we need two hydrogen atoms. And the barium hydroxide requires two hydroxide ions.

These brackets are important. Without them, you'd think that there's just one oxygen - O - and two hydrogens - H. The brackets show that there are two of both the oxygen and the hydrogen. Sometimes we also want to show if the substances are in solid, liquid, or gas form; or whether they are dissolved in water. Barium is a metal, and solid.

We mark that with a lowercase 's', short for the word solid. Water is a liquid. We show this with a lowercase 'l' -- meaning liquid. One of the products we get -- hydrogen gas -- is marked with a lowercase 'g'. For gas, that is.

The barium hydroxide is dissolved in water. We mark that with 'a-q', which stands for aqueous. It's not only in chemical reactions that the product might be in a different state than the reactants. When you bake a cake, for example. Egg and oil are in liquid form, while flour, baking powder, and sugar are solids to start with.

The result -- the tasty cake -- is -- hopefully -- also in solid state. And that which made the dough rise -- carbon dioxide -- is a gas that is created by the baking soda.