Combination Reaction

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.

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)

2. 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

• Formation of magnesium carbonate from magnesium oxide and Carbon Dioxide

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

• Formation of ammonium sulphate from ammonia gas and sulphuric acid

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.