Types of Chemical Reactions

Types of Chemical Reactions : Core Concepts

This article will cover the main classifications of chemical reactions: synthesis reaction, decomposition reaction, single replacement reaction, and double replacement reaction. We also discuss what is a combustion reaction, precipitation reaction, and acid base reaction.


  • synthesis reaction- a reaction that occurs when two atoms interact to form one atom
  • decomposition reaction– a reaction that occurs when a compound breaks down into two or more atoms
  • combustion reaction – when a substance reacts with oxygen, forming light and heat in the form of fire
  • single replacement reaction– a reaction that occurs when a new compound is formed when one element is substituted for another element in a compound, creating a new element and a new compound as products
  • double replacement reaction – a reaction in which the cationic or the anionic species switch places, creating two new products
  • neutralization (acid base reaction)- a double replacement reaction in which an acid reacts with a base to form water and salt
  • precipitation reaction– a double replacement reaction in which forms a solid from two miscible liquids

The Four Basic Types of Chemical Reactions

Types of Chemical Reactions
Types of Chemical Reactions

Synthesis Reaction

A synthesis reaction occurs when two reactants interact to form one product. The product created is different from both of the reactants. The general equation represents this type of reaction:

 \ch{A + B ->AB}

In most cases, synthesis reactions release energy. Reactions that release energy are considered exothermic. A typical example of a synthesis reaction is the formation of table salt. Sodium and chlorine ions interact to form sodium chloride.

 \ch{Na+ +  Cl- ->NaCl}

Decomposition Reaction

A decomposition reaction occurs when the reactant breaks down into simpler products. Here is the general equation that represents this type of reaction:

 \ch{AB ->A + B}

Unlike synthesis reactions, decomposition reactions require energy to break the bonds present in the reactant. Reactions that require an input of energy are endothermic. A common example of a decomposition reaction is the decomposition of hydrogen peroxide. The decomposition of hydrogen peroxide results in water and oxygen gas. This is shown in the following equation:

 \ch{2H2O2 ->2O2 + B}

Video showing the decomposition of hydrogen peroxide

Single replacement Reaction

Single replacement reactions occur when a single element replaces an element in another compound. This produces a new compound and a new element. This type of reaction is represented by the general equation

 \ch{AB + C -> AC+ B}

In this equation, C replaces B in the reaction, and B is now a single element. A common example of a single replacement reaction is the reaction of Tin chloride and zinc. In the reaction, zinc replaces tin to form zinc chloride and tin as a single element. The chemical equation of this reaction is:

 \ch{SnCl2 + Zn -> ZnCl2 + Sn2}

Video of a Single replacement reaction

Video showing the single displacement of hydrogen by elemental samarium. Subscribe for more great chemistry videos!

Double replacement Reaction

A double replacement reaction exchanges ionic species in two compounds to form two completely new compounds. Double replacement reactions swap cations or the anions, but not both. The general equation that represents this type of reaction:

 \ch{AB + CD -> AC + BD}

An example of a double-replacement reaction is the reaction between Lead nitrate and Potassium iodide. The lead cation and potassium cation switch places.

 \ch{Pb(NO3)2 + 2 KI -> PbI2 + 2 KNO3}

Precipitation Reactions

Precipitation and neutralization are both double replacement reactions. These reactions both result in two completely new compounds through double replacement. A precipitation reaction occurs when two soluble compounds mix to form an insoluble solid. The solid that separates from the solution is called the precipitant. A classic example of a precipitation reaction is Silver nitrate’s reaction with Potassium chloride, which forms silver chloride, a white solid.

 \ch{AgNO3(aq) + KCl(aq) -> AgCl(s) + KNO3(aq)}

Video of a Precipitation Reaction

This video shows a beautiful precipitation reaction. Subscribe for more great chemistry videos!

Acid Base Reactions

Acid base reactions, or neutralization reactions are double replacement reactions that occur between acids and bases. Typically, acid-base neutralizations produce water and a salt. A common example of neutralization is between hydrochloric acid, a strong acid, sodium hydroxide, a strong base. Learn more about acid-base neutralization reactions.

 \ch{HCl + NaOH -> NaCl + H2O}

Combustion Reactions

Combustion reactions are those that involve the burning of compounds. A reactant, usually a hydrocarbon, reacts with oxygen gas (O2), to produce carbon dioxide gas (CO2) and water vapor (H2O). Combustion reactions also produce energy in the form of heat and/or light.

Example: the combustion of fuel propels the movement of cars. C8H18 (octane), or gasoline, reacts with oxygen gas in the air to produce carbon dioxide gas and water vapor, but most importantly, energy.

2C8H18 + 25O2 → 16CO2 + 18H2O

Further Reading

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