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If the things are going perfect in our world, then the reason behind is the ever-going chemical reactions. It would not be wrong to say that these types of chemistry reactions are a vital part of our culture, technology, and life itself.

Smelting iron, burning fuels, pottery and glass manufacturing, production of cheese and wine, and brewing processes are typical chemical reaction examples. We balance complex chemical equations for getting desired results.

These processes have been used for thousands of years. But, to understand the process thoroughly, you first have to learn the ropes.

What is a chemical reaction?

A chemical reaction can be defined as a process in which one or more substances undergo a chemical change, such as a change in the structure or positioning of atoms.

So, one or more new substances come into being. The substances which take part in the reaction are reactants and the resulting substances are products. Such as

A + B (reactants) → AB (products)

These substances could be either chemical compounds or elements. The simplest and basic chemical reactions occurring in our surroundings are as follows.

H2 + O2 → 2H2O (between elements)
2Na + Cl2 → 2NaCl (between elements)
HCl + NaOH → NaCl + H2O (between compounds)

Types of chemical reactions

The changes which occur within the reactants during a chemical reaction determine the types of chemical reaction and the nature of products.

Based on this rule, chemical reactions are often divided into five common types.

Most of the products we get in our daily lives come into existence by going through one of these five reactions.

And if a person learns about these basic chemical reactions, dealing with chemical equations would not be a problem. These common types of chemical reactions are as follows

  • Combination reaction
  • Decomposition reaction
  • Combustion reaction
  • Single replacement reaction
  • Double replacement reaction


The question which arises here is how someone can predict the type of chemical reaction by seeing a chemical equation?

Answer: Analyze the nature of reactants and products taking part in the reaction. You will be able to predict the types of reaction occurring among them. In some cases, there are even such reactions that fall into more than one category.


Combination reaction

As the name indicates, in this type of chemical reaction, two or more substances combine to form a single and all-new substance.

Since a new substance is being synthesized, such reactions are also being referred to as synthesis reactions. To illustrate it further, let's have a look at the general equation of combination reaction.

A + B → AB

Some common combination or synthesis reaction examples are as follows

2Na + Cl2M → 2NaCl
2Zn + O2 → 2ZnO
H2 + O2 → 2H2O

Quick tips:

  • Always remember that in combination reactions, two elements react to form a compound. So, whenever you notice a chemical reaction where two elements interact to form a single compound, know that it is a combination reaction. This can be processed by using chemical equation balancer online.

Related: What is the general chemical equation for an endothermic reaction?

Decomposition reaction

The term "decompose" means "to break down." Hence, in decomposition reactions, a single substance is broken down into its constituents or one or smaller units.

In such sort of reactions, the reactant is always a bigger chemical compound that comprises many elements. These elements may get separated from each other simply, such as

AB → A + B

Or may broke into simpler substances such as

ABX → AB + X

The common examples of decomposition reactions are as follows

CaCO3 → CaO + CO2
2H2O → H2 + O2
2AgBr → 2Ag + Br2

Quick tips:

  • Remember that the binary compounds always break into two elements while bulkier compounds form latterly.
  • Whenever you notice that there is only one reactant in the reaction mixture, which is getting broken down into simpler units, know that decomposition is occurring.
  • Decomposition reactions are nothing other than the reversed combination reactions.

Related: How to balance chemical equations step by step?

Combustion reaction

Whenever the term combustion appears, always think of a burning process. In this type of reaction, a chemical substance reacts with oxygen and burns into simpler units. They release energy in the form of heat and light.

The simplest example of this reaction is the burning of fossil fuel. Where fuel burns in the presence of oxygen and releases energy along with the by-products as follows:

Hydrocarbons + oxygen → carbon dioxide + water + heat
CH4 + 2O2 → CO2 + 2H2O
C3H8 + 5O2 → 3CO2 + 4H2O

Quick tips:

  • All the reactions where energy is released in heat and light is due to the combustion phenomenon.
  • Combustion of hydrocarbons always results in products such as water and carbon dioxide.
  • Oxygen is always present at the left side of the equation in combustion reactions.

Single-replacement reaction

In this type of reaction, one element from one of the reactants detaches and bind to another reactant such as follows

AC + B → A + BC

As indicated by the equation, C detaches from the first reactant (AC) and gets attached to the B to form the final product (BC).

Since element A is replaced by element B, the reaction is referred to as a replacement reaction. Some examples of single replacement reactions are as follows

Zn + 2HCl → ZnCl2 + H2
Br2 + 2KI → 2KBr + I2

Quick tips:

  • Metal can only replace another metal atom, as described in the above general equation. If A is metal, B will surely be a metal atom.
  • A non-metal will always replace another non-metal. So if confused about the final products of a single replacement reaction. Thoroughly analyze the nature of replacing elements to predict the correct product.
  • When a single replacement reaction occurs between metal and acid, hydrogen gas is formed as a by-product along with the main replacement product. Such as
    Zn + 2HCl → ZnCl2 + H2 (g)

Related: How to balance redox reaction in a basic solution?

Double replacement reaction

Such reactions always take place between ionic compounds, and, as the name implies, two atoms get replaced in the reactants.

Since the ionic compounds are reacting with each other, the replacement of positive and negative ions of each compound occur to form new compounds such as

A+B- + C+D- → C+B- + A+D-

Some examples of double replacement reactions are as follows

AgNO3 + NaCl → NaNO3 + AgCl (ppt.)
KBr + AgNO3 → KNO3 + AgBr (ppt.)

Quick tips:

  • Double replacement reactions always occur in aqueous solutions. After replacement, the two products separate from each other since one of them comes out as sediment.
  • When you observe a chemical reaction where ion-displacement occurs, and at least one final product comes out as sediment. It means the reaction occurring between them is a double replacement reaction.