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Combination Reaction

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Last updated date: 09th Apr 2024
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Combination Reaction: An Introduction

Chemical reactions are crucial events in the universe. From the growing of a plant, the photosynthesis, ripening of fruit, and the final Decomposition of a plant, every stage is composed of a number of chemical reactions.


When coming to animals, their respiration, digestion, and reproduction are all accompanied by a chemical reaction. Hence a world without chemical reactions cannot be possible. There are several types of chemical reactions like decomposition reactions, disproportionation reactions, combination reactions, etc. This article is all about the combination reaction, types of combination reactions and combination reaction examples.

What is a Combination Reaction?

A combination reaction can generally be a chemical reaction where two or more elements or compounds combine to form a single products. Hence, we can say that a combination reaction occurs due to a combination of elements or compounds. Or combination reactions are reactions in which a single compound is formed due to a combination between two or more elements or compounds.


Hence a general combination reaction can be represented by the equation

A + B → AB. This is the equation of a combination reaction.

In combination reactions, there is no limitation in the number of reactants that can participate in the reaction. Also, the reaction is generally exothermic because, during a combination reaction, a new bond is formed between the reactant molecule that leads to the release of heat.


For example, the formation of the salt barium fluoride by the combination of barium metal and fluorine gas is a highly exothermic reaction.


Ba (s) + F2 (g) → BaF2 (s)


Cause of Chemical Combination

Elements or compounds combine together, and they form a product during a chemical reaction. What is the motive of this chemical combination? Or why do chemical combinations occur? The answer to this question is simple every element or compound take part in a chemical combination to attain stability. As per the lewis theory, an atom attains stability if it gains the noble gas configuration.


Hence, during a chemical reaction, electrons are shared between atoms, and they achieve a stable electronic configuration. Hence the tendency of an atom of various elements to attain stability by acquiring a noble gas configuration is the cause of chemical combination.


Types of Combination Reactions

There are 3 ways in which a combination reaction can take place.

  • Combination of two or more elements.

  • Combination of two or more compounds.

  • Combination of a compound with an element.


Let's look at each type in detail.

  • Combination of more than two elements: In this type, two or more elements combine together and form a single compound.

for example

  1. Carbon and oxygen combine to form Carbon Dioxide gas

C (g) + O2 (g) CO2 (g)

  1. Hydrogen and oxygen combine to form water

H2 (g) + O2 (g) → 2H2O (l)

  • Combination reaction between two compounds: In this, two compounds combine together and form a new compound.

E.g. The formation of calcium hydroxide (slaked lime) by the reaction of calcium oxide (quick lime) and water.

CaO (s) + H2O(l) → Ca(OH)2 (s)

  • Combination reaction between a compound and an element: A compound reacts with an element and forms a new compound. Formation of Carbon Dioxide gas from the compound carbon monoxide and the element oxygen is an example of this type of combination reaction

2 CO(g) + O2 (g) → 2 CO2 (g)


Properties of Combination Reaction

  • In combination reactions, the number of reactants participating in the chemical reaction is not limited.

  • The product of a combination reaction between a metal and a non-metal is always an ionic solid.

e.g. Burning of magnesium in air and forming magnesium oxide.


Examples of Combination Reaction

2MgO + 2 CO2 → 2 MgCO3

  • Formation of lithium sulphide from lithium and sulphur

Li + S2 → 2 LiS

  • Formation of ammonia from nitrogen and hydrogen

N2 + 3H2 → 2 NH3

2NH3 + H2SO4 → (NH4 )2 SO4


Key Features

  • Combination reactions are when two or more elements or compounds combine to form a new compound.

  • Combination reactions between two elements, two compounds or between an element and a compound are the three types of combination reaction.

  • Elements or compounds combine together to attain stability.

Competitive Exams after 12th Science

FAQs on Combination Reaction

1. What are the three laws that govern a chemical combination?

  • Law of Conservation of Mass: According to this law mass can neither be created nor be destroyed it can transform from one form to the other

  • Law of Definite Proportion: The law states that the proportion of an element by weight in a compound always remains exactly the same irrespective of its source, origin or quantity

  • Law of Multiple Proportions:  According to this law when two elements combine together to form more than one compound the masses of these elements in the compounds are in the ratio of small whole numbers

2. Give any three real-life examples of combination reactions?

  • Burning of Coal: It is a combustion reaction and in all combustion reactions the product is carbon dioxide.

  • Acid Rain: If our atmosphere contains pollutants like sulphur oxide during the rainfall rainwater combines with these sulphur oxides and forms sulphuric acid  hence the rainwater contains some acidic contents

  • Calcium Hydroxide Production: Calcium hydroxide is a white-coloured powder which can be used as a filling of a root canal during dental treatment. Calcium hydroxide is formed by the combination reaction between calcium oxide and water. Calcium hydroxide found applications in sewage treatment, food processing and paper production.

3. What are the industrial applications of combination reactions?

Elements or compounds combine so as to attain stability by acquiring a stable noble gas configuration. Combination reactions are found useful in various fields. Combination reactions can be used to produce very stable ionic compounds. Also, combination reactions were found useful in soap production and the production of ammonia through the Haber process.

Ferrous sulphide is a common pigment in hair color and is used to paint ceramic pots. It is formed by the combination reaction between iron and sulphur. Sodium hydroxide is formed by the combination reaction of sodium oxide and water found in applications in the dye, petroleum products, paper, soap production and in explosives.