Types of Chemical Reactions

Chemical reactions take place at the molecular level, when the atoms and molecules of the things you start with (reactants) turn into something new (products). All chemical reactions can be split generally into six different categories:

• Combustion
• Synthesis
• Decomposition
• Single Displacement
• Double Displacement
• Acid-Base Neutralization

Each of these reactions have unique characteristics. based on certain criteria, you should be able to determine which reaction is happening.

Combustion reactions always include two things: oxygen as a reactant and energy (in the form of heat) as a product. In most cases their products include Carbon dioxide (CO₂) and water (H₂O). These reactions often involve something visibly burning or exploding, which make them pretty cool to look at, as seen in the video to the right.

Examples:

Burning Methanol (rubbing alcohol)

CH₃OH + O₂ --> CO₂ + 2H₂O+ HEAT

Burning Napthalene:

C₁₀H₈ + 12 O₂ ---> 10 CO₂ + 4H₂O + HEAT

Synthesis reactions are when two (or more) single-element molecules combine to form one large molecule.  It is something like the opposite of a decomposition reaction.

Examples:

A silver spoon tarnishes. The silver reacts with sulfur in the air to make silver sulfide, the black material we call tarnish.

2Ag + S --> Ag₂S

An iron bar rusts. The iron reacts with oxygen in the air to make rust.

4Fe + 3O₂ --> 2Fe₂O₃

Decomposition reactions are when one large molecule decomposes or breaks apart into many parts.  This can happen through natural processes (such as natural fermentation or nuclear half-life) or aided by a catalyst.

Examples:

Fermentation-Glucose (simple sugar) ferments to ethyl alcohol and carbon dioxide. The sugar in grapes or from grain ferments (with yeast as a catalyst) to make the alcohol and carbon dioxide. The carbon dioxide is the gas that bubbles out of beer or champagne.  

C₆H₁₂O₆ --> 2C₂H₅OH + 2CO₂

Displacement reactions can be viewed as people going to a party.  A single displacement reaction is like when a guy and a girl come to a party together, and then one of them leaves with another person.

Almost all acid-metal reactions are single displacement reactions.

Examples:

Silver nitrate and Zinc make Silver and Zinc nitrate

2AgNO₃ + Zn --> 2Ag+ Zn(NO₃)₂

Aluminum and Hydrochloric Acid make Aluminum Chloride and Hydrogen gas (See reaction in video)

2Al + 6HCl --> 2AlCl₃ + 3H₂

Double Displacement reactions are like a "swinger" party.  Two pairs of elements come to the party attached to each other, but both end up with someone else from the other couple. 

Examples:

Iron Oxide (rust) and Hydrochloric Acid make Iron chloride and water

Fe₂O₃ + 6HCl --> 2FeCl₃ + 3H₂O

Acid-base reactions are generally a special type of double displacement reaction, where water is produced.

Examples:

An antacid (calcium hydroxide) neutralizes stomach acid (hydrochloric acid).

Ca(OH)₂ + 2HCl --> CaCl₂ + 2H₂O

Vinegar and Baking Soda

CH₃COOH + NaHCO₃ --> H₂O + NaOCOCH₃ + CO₂ (note that this looks like a combustion reaction because it has water and carbon dioxide as products, but it does not produce heat)

I have created a handy-dandy flowchart located below for just such a question.  I made it myself, and I give anyone permission to use it for whatever purpose you choose.