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Chemical reactions

What is a chemical reaction?

A chemical reaction is a process that converts one or more chemicals, known as reactants, into new compounds, known as products, having differed chemical and physical properties. Bonds between atoms are broken and new bonds are established during a chemical reaction, resulting in the formation of new compounds. Chemical reactions can be detected by changes in color, temperature, light emission, gas production, or precipitate formation (a solid formed from a solution). A multitude of conditions, such as heat, light, electricity, or the inclusion of a catalyst, can produce these reactions. Many natural processes use chemical reactions, which are utilized in a wide range of industrial and commercial applications.

What occurs during a chemical reaction?

• The formation of new compounds by the interaction of two or more chemicals.

• The transformation of one substance into two or more substances.

• The reorganization of starting compounds in order to generate new substances.

Types of chemical reactions

They are categorized into four kinds based on the nature of the chemical alteration. These are listed below.

  • Chemical combination reactions
  • Chemical decomposition reactions
  • Single displacement reactions
  • Double displacement (Double decomposition) reactions

Chemical Combination Reactions

A synthesis reaction, also known as a chemical combination reaction, is a type of chemical reaction in which two or more reactants combine to generate a single, more complicated result. In other words, the formation of chemical bonds between two or more substances results in the formation of a new compound.

The general equation for a chemical combination reaction

A + B → AB

To clarify, A and B are the reactants, and AB is the final product.

Chemical combination reactions are often exothermic, releasing energy in the form of heat or light, and they are frequently spontaneous under the correct conditions. Depending on the reaction, they can be started by heat, light, electricity, or a catalyst.

Examples of chemical combination reactions

The combination reaction of hydrogen and oxygen gases results in water.

Equation for water formation

2H2 + O2 → 2H2O

In this reaction, hydrogen and oxygen react to form water, a single product.

Carbon and Oxygen React to Create Carbon Dioxide:

Equation for carbon dioxide formation

C + O2 → CO2

In this reaction, carbon and oxygen react to form carbon dioxide, a single product.

Magnesium reacts with oxygen in the air forming magnesium oxide

Equation for magnesium oxide formation

Magnesium + oxygen 🡪 magnesium oxide

2Mg + O2 🡪 2MgO

Two components have joined to generate a new compound in this case.

Definition for chemical combination reaction

A chemical combination reaction is the synthesis of a new compound by the combination of elements with elements, elements with compounds, or compounds with compounds.

More examples for chemical combinations reactions

Equation for carbon dioxide formation

carbon + oxygen 🡪 carbon dioxide

C + O2 🡪 CO2

Equation for calcium hydroxide formation

calcium oxide + water 🡪 calcium hydroxide

CaO + H2O 🡪 Ca(OH)2

Equation for hydrogen chloride formation

hydrogen + chlorine 🡪 hydrogen chloride

H2 + Cl2 🡪 2HCl

Equation for carbon monoxide formation

carbon dioxide + carbon 🡪 carbon monoxide

CO2 + C 🡪 2 CO

Chemical Decomposition Reactions

What is chemical decomposition reaction

A chemical decomposition reaction, also known as a decomposition reaction, is a type of chemical reaction in which a single compound breaks down into two or more simpler substances. In other words, this type of reaction includes the breaking of chemical bonds within a single component, resulting in the formation of several products.

General equation for a chemical decomposition reaction

AB → A + B

Specifically, if AB is the reactant, then A and B are the end results.

Under the effect of heat, potassium permanganate decomposes to generate various compounds and elements.

Equation for potassium permanganate decomposition

potassium permanganate 🡪 potassium manganate + manganese dioxide + oxygen

2KMnO4 🡪 K2MnO4 + MnO2 + O2

Definition for chemical decomposition reaction

A chemical decomposition process occurs when a substance decomposes into simpler compounds or elements, or compounds and elements.

More examples for chemical decomposition reactions

Equation for calcium carbonate decomposition

calcium carbonate 🡪 calcium oxide + carbon dioxide

CaCO3 🡪 CaO + CO2

Equation for hydrogen peroxide decomposition

hydrogen peroxide 🡪 water + oxygen

2H2O2 🡪 2 H2O + O2

Equation for silver oxide decomposition

silver oxide 🡪 silver + oxygen

2Ag2O 🡪 4Ag + O2

Chemical decomposition reaction examples

Calcium carbonate breaks down into calcium oxide and carbon dioxide gas when heated. (thermal decomposition)

Equation for decomposition of calcium carbonate

CaCO3 → CaO + CO2

In this reaction, calcium carbonate decomposes into calcium oxide and carbon dioxide, two separate products.

Electrolysis of water, which involves the decomposition of water into hydrogen gas and oxygen gas:

Equation for decomposition of water

2H2O → 2H2 + O2

In this reaction, water is decomposed into hydrogen gas and oxygen gas, two separate products.

Chemical decomposition reactions in industry

Chemical decomposition reactions are significant in a variety of industrial operations, ranging from the manufacture of chemicals and materials to the generation of energy.

Production of chemicals:

Many chemical compounds are produced by decomposition reactions.

For example, the production of sodium carbonate involves heating sodium bicarbonate to produce carbon dioxide gas and sodium carbonate:

2 NaHCO3 → Na2CO3 + H2O + CO2

Extraction of metals:

Some metals are extracted from their ores by decomposition reactions. For example, zinc oxide is reduced to zinc metal using carbon monoxide gas in the Mond process:

ZnO + CO → Zn + CO2

Generation of energy:

Fuel cells rely on decomposition reactions to generate electricity. For example, in a hydrogen fuel cell, hydrogen gas is decomposed into protons and electrons, which then react with oxygen to produce water and electricity:

2H2 + O2 → 2H2O + energy


Polymerization processes involve the breakdown of a monomer into smaller molecules, which subsequently react with one another to produce a polymer. Polyethylene, for example, is made by decomposing ethylene to generate free radicals, which subsequently react with one another to form a polymer.:

nCH2=CH2 → -(-CH2-CH2-)n

Decomposition of pollutants:

In environmental science, decomposition reactions can be used to break down pollutants in the environment. For example, the decomposition of ozone in the upper atmosphere helps to protect the Earth from harmful UV radiation.

Single Displacement Reactions

What is Single Displacement Reaction

A single displacement reaction is a type of chemical reaction in which one element or ion in a compound is replaced by another element or ion.

General equation for Single Displacement Reactions

A + BC → B + AC

In this equation, A is the element or ion that displaces B in the compound BC to form the new compound AC.

Examples for Single Displacement Reactions

when iron is placed in a solution of copper sulfate, a single displacement reaction occurs. The iron atom replaces the copper atom in the compound, forming iron sulfate and copper metal:

Equation for iron and copper sulfate reaction

Fe + CuSO4 → FeSO4 + Cu

In this reaction, the iron (Fe) displaces the copper (Cu) in the compound copper sulfate (CuSO4), forming iron sulfate (FeSO4) and copper metal (Cu).

Single displacement reactions can also occur between two ionic compounds if the displaced element or ion is less reactive than the displacing element or ion.

For example, when zinc metal is added to a solution of hydrochloric acid, a single displacement reaction occurs, producing zinc chloride and hydrogen gas:

Equation for zinc and hydrogen chloride reaction

Zn + 2HCl → ZnCl2 + H2

In this reaction, the zinc (Zn) displaces the hydrogen (H) in the compound hydrochloric acid (HCl), forming zinc chloride (ZnCl2) and hydrogen gas (H2).

Zinc metal interacts with copper sulphate to liberate copper metal and generate zinc sulphate.

Equation for zinc and copper sulphate reaction

Zinc + copper sulphate 🡪 zinc sulphate + copper

Zn + CuSO4 🡪 ZnSO4 + Cu

Definition for single displacement reaction

Single displacement reactions occur when an element displaces another element in a compound, occupying its position and creating another compound.

Examples for single displacement reactions

Equation for magnesium and copper sulphate reaction

magnesium + copper sulphate 🡪 magnesium sulphate + copper

Mg + CuSO4 🡪 MgSO4 + Cu

Equation for magnesium and hydrogen chloride reaction

magnesium + hydrogen chloride 🡪 magnesium chloride + hydrogen

Mg+ 2HCl 🡪 MgCl2 + H2

Equation for potassium bromide and chlorine reaction

potassium bromide + chlorine 🡪 potassium chloride + bromine

2KBr + Cl2 🡪 2KCl + Br2

Double Displacement Reactions

what is Double Displacement Reaction

A double displacement reaction is a type of chemical reaction where two ionic compounds in a solution react and exchange ions to form two new ionic compounds.

Common reaction for the Double Displacement Reactions

General equation:

AB + CD → AD + CB

In this equation, A and C are positive ions (cations), while B and D are negative ions (anions).

When barium chloride and sodium sulphate combine, barium sulphate and sodium chloride are formed.

Equation for Barium chloride and sodium sulphate reaction

barium chloride + sodium sulphate 🡪 barium sulphate + sodium chloride

BaCl2+ Na2SO4 🡪 BaSO4 + 2NaCl

Definition for double displacement reaction

A double displacement reaction occurs when an element or radical in one compound exchanges places with an element or radical in another compound.

Examples of double displacement reactions

when sodium chloride (NaCl) is mixed with silver nitrate (AgNO3), a double displacement reaction occurs, producing silver chloride (AgCl) and sodium nitrate (NaNO3):

NaCl + AgNO3 → AgCl + NaNO3

In this reaction, the sodium (Na) from the sodium chloride (NaCl) combines with the nitrate (NO3) from the silver nitrate (AgNO3) to form sodium nitrate (NaNO3), while the silver (Ag) from the silver nitrate (AgNO3) combines with the chloride (Cl) from the sodium chloride (NaCl) to form silver chloride (AgCl).

Double displacement reactions between an acid and a base can also occur, creating a salt and water.

For example, when hydrochloric acid (HCl) is mixed with sodium hydroxide (NaOH), a double displacement reaction occurs, producing sodium chloride (NaCl) and water (H2O):

HCl + NaOH → NaCl + H2O

In this reaction, the hydrogen (H) from the hydrochloric acid (HCl) combines with the hydroxide (OH) from the sodium hydroxide (NaOH) to form water (H2O), while the sodium (Na) from the sodium hydroxide (NaOH) combines with the chloride (Cl) from the hydrochloric acid (HCl) to form sodium chloride (NaCl).

Equation for Ferrous sulphate and sodium hydroxide reaction

Ferrous sulphate + sodium hydroxide 🡪 ferrous hydroxide + sodium sulphate

FeSO4 + 2NaOH 🡪 Fe(OH)2 + Na2SO4

Equation for calcium chloride and sodium carbonate reaction

calcium chloride + sodium carbonate 🡪 calcium carbonate + sodium chloride

CaCl2 + Na2CO3 🡪 CaCO3 + 2NaCl

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Anuradhika Lakmali

Anuradhika Lakmali is a co-founder of Science A Plus learning network. She is working as a government teacher and has interest in chemistry, biology, phisics and self development.