 In this video we're going to classify some chemical reactions into a small number of different types. We can't classify every reaction using these types but they are a few simple but common examples that will help you get your head around different kinds of reactions. So let's start with the two simplest reactions, putting stuff together and taking it apart. An example of putting stuff together would be the reaction between zinc and sulphur. You mix zinc powder and sulphur powder together, you heat it to get the reaction going and it then transforms into the ionic compound zinc sulfide. This kind of reaction where you combine two reactants into one product is called a combination. The opposite to a combination reaction is a decomposition reaction. In this type of reaction you take a single compound and you make it decompose to give two or sometimes more products. An example of one of these types of reaction is the decomposition of water. This is done by passing electricity through water. The bonds holding the water molecules together are broken and the atoms rearrange to give pure hydrogen, H2 remember, and oxygen which is O2. The next type of reaction you might encounter is called a displacement or sometimes a replacement reaction and there are two kinds, single and double displacements. These types of reactions involve ionic compounds and the key feature is that ions or atoms will swap places with each other in the compounds. Let me show you what I mean. Let's first look at single displacement reactions. In this reaction one element is displaced from a compound by another one. You can see I've represented this by the green circle here kicks out the blue circle from this compound and takes its place. A commonly demonstrated example of this kind of reaction is that between zinc and copper sulfate. This picture from the science photo library shows this reaction happening. Copper sulfate is blue and soluble in water so the blue colored solution near the top of the test tube is copper sulfate dissolved in water. The shiny metals sticking out of the copper sulfate solution is zinc metal and these are our two reactants, zinc and copper sulfate. You can see that where the zinc has come into contact with the copper sulfate its surface has become covered with a reddish gunk. This stuff is actually tiny copper crystals. At the bottom of the test tube you can see that the solution has lost its color. The blue copper sulfate has been transformed into colorless zinc sulfate while the copper ions that used to be part of the copper sulfate have now been precipitated out as pure copper metal. And those are our two products, the pure copper and the zinc sulfate which is now dissolved in solution.