Simple Chemical Reactions

Synthesis Reaction or Direct Combination Reaction

One of the main types of chemical reactions is a synthesis or direct combination reaction. As the name implies, simple reactants make or synthesize a more complex product. The basic form of a synthesis reaction is:

A + B → AB

A simple example of a synthesis reaction is the formation of water from its elements, hydrogen, and oxygen:

2 H₂(g) + O₂(g) → 2 H₂O(g)

Another good example of a synthesis reaction is the overall equation for photosynthesis, the reaction through which plants make glucose and oxygen from sunlight, carbon dioxide, and water:

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

Decomposition Chemical Reactions

The opposite of a synthesis reaction is a decomposition or analysis reaction. In this type of reaction, the reactant breaks down into simpler components. A telltale sign of this reaction is that you have one reactant, but multiple products. The basic form of a decomposition reaction is:

AB → A + B

Breaking water into its elements is a simple example of a decomposition reaction:

2 H₂O → 2 H₂ + O₂

Another example is the decomposition of lithium carbonate into its oxide and carbon dioxide:

Li₂CO₃ → Li₂O + CO₂

Single Displacement or Substitution Chemical Reactions

In a single displacement or substitution reaction, one element replaces another element in a compound. The basic form of a single displacement reaction is:

A + BC → AC + B

This reaction is easy to recognize when it takes the form of:

element + compound → compound + element

The reaction between zinc and hydrochloric acid to form hydrogen gas and zinc chloride is an example of a single displacement reaction:

Zn + 2 HCl → H₂ + ZnCl₂

Double Displacement Reaction or Metathesis Reaction

A double displacement or metathesis reaction is just like a single displacement reaction, except two elements replace two other elements or "trade places" in the chemical reaction. The basic form of a double displacement reaction is:

AB + CD → AD + CB

The reaction between sulfuric acid and sodium hydroxide to form sodium sulfate and water is an example of a double displacement reaction:

H₂SO₄ + 2 NaOH → Na₂SO₄ + 2 H₂O

Combustion Chemical Reactions

A combustion reaction occurs when a chemical, usually a hydrocarbon, reacts with oxygen. If a hydrocarbon is a reactant, the products are carbon dioxide and water. Heat is released, too. The easiest way to recognize a combustion reaction is to look for oxygen on the reactant side of a chemical equation. The basic form of a combustion reaction is:

hydrocarbon + O₂ → CO₂ + H₂O

A simple example of a combustion reaction is the burning of methane:

CH₄(g) + 2 O₂(g) → CO₂(g) + 2 H₂O(g)

More Types of Chemical Reactions

In addition to the 5 main types of chemical reactions, there are other important categories of reactions and other ways to classify reactions. Here are some more kinds of reactions:

• acid-base reaction: HA + BOH → H2O + BA
• neutralization reaction: acid + base → salt + water
• oxidation-reduction or redox reaction: one atom gains an electron while another atom loses an electron
• isomerization: structural arrangement of a molecule changes, although its formula remains the same
• hydrolysis: AB + H₂O → AH + BOH