There are 117 elements, these can combine to create thousands of compounds and yield chemical reactions, lots of them. Lucky for the sake of our brains, there are only six main chemical reactions that are essential. The following chemical reactions are the ones that you really need to know to understand the vast world of chemical reactions.
1. Combination reaction, also know as a synthesis reaction, is exactly that, a reaction in which two or more reactants combine to create a more complex substance. It can be between two elements, two compounds or an element and a compound. This is one of the simplest reactions and the easiest to remember.
A combination reaction looks like this, A + B = AB, an example is 2Mg + O = 2MgO.
2. Decomposition reaction, also a relatively easy one, is the exact opposite of the combination reaction. It is when a reactant breaks down into its simpler products, in these the reactant is complex and the products are simple.
A Decomposition reaction looks like this, AB = A + B, an example is 2HgO = 2Hg + O2.
3. Single-replacement reaction is when an uncombined element replaces a combined element in its compound. The compound must be aqueous and the displaced element must be less active than the other. The product is a separate element and slightly different compound.
A single-replacement reaction ooks like this, A + BC = BA + C, an example is 2K + 2H2O = 2KOH + H2.
4. Double-replacement reaction is one of the most complicated ones. It is when elements of two compounds, switch places. These compounds must be ionic and the react by switching cations to make totally new compounds. They are made propelled by the formation of a gaseous product, water or precipitate. In the reactant, you must make sure that you switch the parts of the compounds, much like the FOIL method in algebra.
A double-replacement reaction looks like this AB + CD = AD + CB, a real example is AgNO3 + KCL = AgCl _ LNO3
5. Combustion Reaction, also a complicated one, is a reaction that uses oxygen and produces energy so that a flame results. Oxygen reacts with an element and the reaction occurs. The products will always be CO2 and H2O and when incomplete C and CO.
A combustino reaction looks like this Ax+By + O2 = xCO2 + H2O, a real example is CH4 + 2O2 = CO2 + 2H2O
Remember that these are not all of the types of chemical reactions, just the important ones, there are lots and lots of others also. Memorize these and you should be a chemical reaction pro!