Types of Chemical Reactions

There are many types of chemical reactions.  Five of the most common are:

synthesis:  two or more reactants combine to form a single product.

A + B à C

decomposition:  one reactant disintegrates (decomposes) to form two or more products:

A à B + C

single replacement (sometimes called single displacement):  atoms of one element replace atoms of another in a compound:

A + BC à AC + B

Most often, AC and BC are ionic compounds, which means A and B are metals, and C is a non-metal or negative polyatomic ion.

As an analogy, imagine that BC are a couple, and C breaks up with B to go out with A.

double replacement (sometimes called double displacement):  when two positive ions (or two negative ions) switch with each other to form two new compounds:

As an analogy, imagine that AX and CY are two couples.   A and B switch boyfriends, so B is now going out with X and A is now going out with Y.

combustion:  a special kind of reaction in which a hydrocarbon (a compound containing carbon and hydrogen) reacts with O₂ (burns, or “combusts”) to form CO₂ and H₂O.  For example:

C₃H₈ (ℓ) + 5 O₂ (g) à 3 CO₂ (g) + 4 H₂O (g) + heat

The internal combustion engine in your car is a special reactor in which octane (C₈H₁₈) combusts in a cylinder, producing heat.  The heat makes the gases inside the cylinder expand.  (Remember the gas laws!)  This pushes the piston down, which makes the car go.