Synthesis Reaction Description Plus Examples

While there are many types of chemical reactions, they all fall into at least one of four broad categories: synthesis reactions, decomposition reactions, single displacement reactions, and double displacement reactions.

A synthesis reaction or direct combination reaction is a type of chemical reaction in which two or more simple substances combine to form a more complex product. The reactants may be elements or compounds, while the product is always a compound.

General Form of Synthesis Reactions

The general form of a synthesis reaction is:

A + B → AB

Examples of Synthesis Reactions

Here are some examples of synthesis reactions:

• Water:
  2 H₂(g) + O₂(g) → 2 H₂O(g)
• Carbon dioxide:
  2 CO(g) + O₂(g) → 2CO₂(g)
• Ammonia:
  3 H₂(g) + N₂(g) → 2 NH₃(g)
• Aluminum oxide:
  4 Al(s) + 3 O₂(g) → 2 Al₂O₃(s)
• Iron sulfide:
  8 Fe + S₈ → 8 FeS
• Potassium chloride:
  2 K(s) + Cl₂(g) → 2 KCl(s)

Recognizing Synthesis Reactions

The hallmark of a synthesis reaction is that a more complex product is formed from the reactants. One easy-to-recognize type of synthesis reaction occurs when two or more elements combine to form a compound. The other type of synthesis reaction happens when an element and a compound combine to form a new compound.

Basically, to identify this reaction, look for a product that contains all the reactant atoms. Be sure to count the number of atoms in both the reactants and the products. Sometimes when a chemical equation is written, "extra" information is given that might make it hard to recognize what is going on in a reaction. Counting numbers and types of atoms makes it easier to identify reaction types.