There are four main types of chemical reactions.

• Combination
• Decomposition
• Replacement
• Double replacement

These can be kind of detailed, so I'll just go over the main ideas. The first kind is called a combination. That's just when two or more simple substances joined together. When hydrogen and oxygen combine to make water, they use this type of reaction.

The next kind is called decomposition. That's when a compound breaks into smaller compounds or elements. When gasoline burns, it breaks down into smaller molecules, water and carbon monoxide.

The third kind is replacement. This is just when part of one element replaces part of a compound. This can be seen when you're cleaning silverware. If you have a tarnished spoon, you can do it that in a bath of hot baking soda solution, in an aluminum pan. Aluminum ions will switch with the silver ions in the tarnish, leaving your spoon completely clean and tarnish free.

The last reaction is double replacement. It is a switch similar to a single replacement, but deals with two compounds exchanging parts. Each compound will split into two ions, and will regroup with an ion from the other compound. This frequently happens with acids and bases. We will discuss that in the next section.

There are a few basic rules that govern chemical reactions. If you don't go into chemistry, you probably won't deal with these much, but I want to briefly mention them. One of the main ones is the Law of Conservation of Matter. That basically means that whatever you put into a chemical reaction will still be there in one form or another at the end of the reaction. Nothing just disappears. Nothing gets destroyed. Only changed. If you do cooking, you are already familiar with this.

Another law is the Law of Definite Proportions. This just means that any compound has the exact same number of elements, in the same proportions. If you took two grains of table salt, and looked at one atom in each, they would both have exactly one part sodium and one part chlorine. Every water molecule always has one oxygen and two hydrogens. You would thing this is obvious, and doesn't need to be a law, but it helps build additional laws later on, so needed to be declared.

The last one I want to mention is the Definition of Equations. It can get tiring writing out sodium and chlorine each time you want to discuss table salt, so scientist use the symbols for the elements (you saw those on the periodic table) to represent those elements. They show the reactions that take place using the symbols instead of the words. The reaction creating table salt might look like this.

1 Na + 1 Cl -------> 1 NaCl

When you are dealing with a large compound, like an amino acid or a protein, this can get really detailed! A lot of chemistry class is learning how to write, create, and predict these equations.

There are several other laws and definitions, but as these deal more with the math aspect of chemistry, we will leave those out for now.