Notes On Types of Chemical Reactions - CBSE Class 10 Science
In general chemical reactions are classified into:    Combination reactions    Decomposition reactions    Single displacement reactions    Double displacement reactions Combination reactions: A combination reaction is one in which two or more reactants combine to form a single product. Combination reactions are again of three types. They are: Combination reactions between elements. Combination reactions between compounds. Combination reactions between elements and compounds. Combination reactions between elements: In these reactions elements were combined to form a product. Examples : Formation of calcium oxide by the combination elements calcium and oxygen. 2Ca + O2 → 2CaO Formation of ammonia by the combination of elements nitrogen and hydrogen. N2 + 3H2 → 2NH3 Combination reactions between compounds: In these reactions compounds were combined to form product. Example: Reaction of calcium oxide in water to form calcium hydroxide CaO + H2O  → Ca(OH)2 Combination reactions between elements and compounds: In these reactions elements and compounds combined to form product. Example: Formation of sulphur trioxide by the combination of sulphur dioxide and oxygen. 2SO2 + O2 →  2SO3 Decomposition reaction: Decomposition reactions are those in which a substance splits into two or more simpler substances. Decomposition reactions are the opposite of combination reactions.  Decomposition reactions are of three types:    Thermal decomposition    Electrolysis    Photolysis Decomposition by the application of heat on a substance is called thermal decomposition.  Example:  Thermal decomposition of calcium carbonate. CaCO3 + Δ (Heating) → CaO + CO2 Decomposition of any substance by passing current through it is called electrolysis.  Example:  Electrolysis of water  2H2O → 2H2 + O2 The decomposition reaction resulting from action of light energy is called photolysis.  Example:  Photolysis of silver chloride 2AgCl  → 2Ag + Cl2 Single displacement reaction:  Single displacement reaction is the one in which one element substitutes or displaces another element in a compound to give new compound. Generally in a single displacement reaction,  less active metal is displaced by a more active metal. It is important to note that in a single displacement reaction, one of the reactants is always an element.  Example:  The reaction of magnesium with copper chloride Mg + CuCl2 →  MgCl2 + Cu Double displacement reaction: The reactions which involves exchange of ions (cations and anions) between the reactants are called double displacement reactions. AB + CD → AC + BD Example: Double displacement reactions classified into different types. They are:  Neutralization reactions Precipitation reactions Gas forming reactions Neutralization reaction: Reaction in which hydrogen ions of an acid react with hydroxide ions of a base to form water is an neutralization reaction.  Example : The reaction of hydrochloric acid with sodium hydroxide. H+Cl–  + Na+OH– → Na+Cl– + H2O Precipitation reaction: Reactions which proceeds through the formation of precipitation are called precipitation reactions. Example: In the reaction of barium chloride with sodium sulphate produces precipitate of barium sulphate along with formation of sodium chloride. BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + NaCl (aq) Gas forming reaction: In these reactions gas is produces as one of the product during reaction. Example: Na2CO3 (s) + 2HCl (aq) → 2NaCl (aq) + H2O (l) + CO2 (g) Based on energy differeneces between reactants and products the chemical reactions are classified into two types. They are exothermic reaction and endothermic reaction. Exothermic reaction: Chemical reactions in which heat energy released are known as exothermic reactions. Burning of methane gas in air produces heat energy. CH4 (g) + 2O2 (g) → CO2 (g) +  2H2O (l)+ heat All combustion reactions are exothermic reactions. Endothermic reaction: Reactions which involves absorption of energy are known as endothermic reactions. Example: Formation of nitric oxide from nitrogen and oxygen. N2 (g)+ O2 (g) + Heat → 2NO  Combustion reaction: Burning of a substance in the presence of oxygen which resulting release of energy is called combustion. Example: Combustion of ethylene gas. C2H4 + 3O2 → 2CO2 + 2H2O Oxidation reaction:  Oxidation reaction involves the addition of oxygen or the removal of hydrogen from a substance. Example:  Rusting of iron Rusting of iron: Iron when reacted with both water and oxygen are present (moist air), corrodes. Its silvery colour changes to a reddish-brown, because hydrated oxides are formed which is commonly called as rust. Reaction showing the formation of rust when reacted with water in presence of oxygen (atmosphere).                         4Fe + 3O₂+ XH₂O → 2Fe₂O₃.XH₂O Reduction reaction: The reaction which involves addition of hydrogen or removal of oxygen from a substance is called reduction reaction. Example:  Photosynthesis is a reduction reaction. Redox reaction: The reactions in which both oxidation and reduction occurring together are known as redox reactions. Example: CuO + H2 → Cu + H2O The above is a redox reaction as copper is reduced and hydrogen is oxidised.

#### Summary

In general chemical reactions are classified into:    Combination reactions    Decomposition reactions    Single displacement reactions    Double displacement reactions Combination reactions: A combination reaction is one in which two or more reactants combine to form a single product. Combination reactions are again of three types. They are: Combination reactions between elements. Combination reactions between compounds. Combination reactions between elements and compounds. Combination reactions between elements: In these reactions elements were combined to form a product. Examples : Formation of calcium oxide by the combination elements calcium and oxygen. 2Ca + O2 → 2CaO Formation of ammonia by the combination of elements nitrogen and hydrogen. N2 + 3H2 → 2NH3 Combination reactions between compounds: In these reactions compounds were combined to form product. Example: Reaction of calcium oxide in water to form calcium hydroxide CaO + H2O  → Ca(OH)2 Combination reactions between elements and compounds: In these reactions elements and compounds combined to form product. Example: Formation of sulphur trioxide by the combination of sulphur dioxide and oxygen. 2SO2 + O2 →  2SO3 Decomposition reaction: Decomposition reactions are those in which a substance splits into two or more simpler substances. Decomposition reactions are the opposite of combination reactions.  Decomposition reactions are of three types:    Thermal decomposition    Electrolysis    Photolysis Decomposition by the application of heat on a substance is called thermal decomposition.  Example:  Thermal decomposition of calcium carbonate. CaCO3 + Δ (Heating) → CaO + CO2 Decomposition of any substance by passing current through it is called electrolysis.  Example:  Electrolysis of water  2H2O → 2H2 + O2 The decomposition reaction resulting from action of light energy is called photolysis.  Example:  Photolysis of silver chloride 2AgCl  → 2Ag + Cl2 Single displacement reaction:  Single displacement reaction is the one in which one element substitutes or displaces another element in a compound to give new compound. Generally in a single displacement reaction,  less active metal is displaced by a more active metal. It is important to note that in a single displacement reaction, one of the reactants is always an element.  Example:  The reaction of magnesium with copper chloride Mg + CuCl2 →  MgCl2 + Cu Double displacement reaction: The reactions which involves exchange of ions (cations and anions) between the reactants are called double displacement reactions. AB + CD → AC + BD Example: Double displacement reactions classified into different types. They are:  Neutralization reactions Precipitation reactions Gas forming reactions Neutralization reaction: Reaction in which hydrogen ions of an acid react with hydroxide ions of a base to form water is an neutralization reaction.  Example : The reaction of hydrochloric acid with sodium hydroxide. H+Cl–  + Na+OH– → Na+Cl– + H2O Precipitation reaction: Reactions which proceeds through the formation of precipitation are called precipitation reactions. Example: In the reaction of barium chloride with sodium sulphate produces precipitate of barium sulphate along with formation of sodium chloride. BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + NaCl (aq) Gas forming reaction: In these reactions gas is produces as one of the product during reaction. Example: Na2CO3 (s) + 2HCl (aq) → 2NaCl (aq) + H2O (l) + CO2 (g) Based on energy differeneces between reactants and products the chemical reactions are classified into two types. They are exothermic reaction and endothermic reaction. Exothermic reaction: Chemical reactions in which heat energy released are known as exothermic reactions. Burning of methane gas in air produces heat energy. CH4 (g) + 2O2 (g) → CO2 (g) +  2H2O (l)+ heat All combustion reactions are exothermic reactions. Endothermic reaction: Reactions which involves absorption of energy are known as endothermic reactions. Example: Formation of nitric oxide from nitrogen and oxygen. N2 (g)+ O2 (g) + Heat → 2NO  Combustion reaction: Burning of a substance in the presence of oxygen which resulting release of energy is called combustion. Example: Combustion of ethylene gas. C2H4 + 3O2 → 2CO2 + 2H2O Oxidation reaction:  Oxidation reaction involves the addition of oxygen or the removal of hydrogen from a substance. Example:  Rusting of iron Rusting of iron: Iron when reacted with both water and oxygen are present (moist air), corrodes. Its silvery colour changes to a reddish-brown, because hydrated oxides are formed which is commonly called as rust. Reaction showing the formation of rust when reacted with water in presence of oxygen (atmosphere).                         4Fe + 3O₂+ XH₂O → 2Fe₂O₃.XH₂O Reduction reaction: The reaction which involves addition of hydrogen or removal of oxygen from a substance is called reduction reaction. Example:  Photosynthesis is a reduction reaction. Redox reaction: The reactions in which both oxidation and reduction occurring together are known as redox reactions. Example: CuO + H2 → Cu + H2O The above is a redox reaction as copper is reduced and hydrogen is oxidised.

#### Activities

Activity 1 Csun.edu has created a  wonderful activity on "Types of Chemical Reactions". In this activity different types of chemical reactions are explained with the help of different examples. Along with this explanation they have given a simple animation which shows how a reaction will takes place. Go To Activity Activity 2 Indstudy1.org has created a laboratory activity on "Types of Chemical Reactions". In this activity various types of chemical reactions are explained with good examples. Each task has a video which contains the laboratory activity done by expert. After watching the video student  also get questions which are related to the task. This laboratory activity is very helpful to the student because it gives a real lab experience. Go To Activity

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