Various types of chemical reactions

Composition reactions
In these reactions, a substance is made from its elements. Most composition reactions are exothermic.

Decomposition reactions
In these reactions a substance is decomposed into the elements. In general these reactions are endothermic.

Ionic reactions / precipitation reactions
Here are reactions in aqueous environment where (free) ions join to form insoluble ionic lattices.

Every chemical reaction can be divided into composition steps and decomposition steps.

Exothermic and endothermic reactions
Exothermic is the reaction where the products have less chemical (internal) energy than the reactants.
endothermic is the reaction where the reactants have less energy than the products.

Acid base reactions
Reactions where H+-transfer takes place, from an acid (donor) to a base (receptor)

Reaction with electron transfer: one or more electrons go from the reductor (donor) to the oxydator (receptor)
If that oxydator happens to be oxygen, we may talk about combustion (direct or indirect).

Hydrolysis and Condensation
In these reactions water participates. Water can be used in hydrolysis and is be liberated in condensation.
Splitting a molecule in two parts, where water is used = hydrolysis
Joining two molecules, where one new molecule is produced and where water is liberated as a product = condensation
Hydrolysis and Condensation are each others opposite.

There is also polyhydrolysis and polycondensation, for example in the production or the decomposition of proteins an of starch.
polyethers or polyesters also can suffer hydrolysis.

Addition and elimination reactions
Also addition and elemination are each others opposite.
If two molecules join by opening an unsaturated bonding, you've got addition.
In elemination two new molecules are made from one, whereby one of those new molecules is unsaturated.

At poly addition, macromolecules are mad; starting substances are always unsaturated monomere molecules.

Certain molecules, (monomeres) of one or more types, connect with each other in large amounts, where macromolecules (possibly copolymeres) are produced. Polyaddition is a form of polymerisation.