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Chemical Reactions and Equations- class 10

Chemical Reactions and Equations

Chemical Reactions and Equations

Chemical Equations

Representation of chemical reaction or chemical change by using symbols and formulae of the substances is called Chemical Equation.

Example: A + B → C + D
In the above equation, A and B are called reactants and C and D are called the products.

During any chemical reaction ,following changes takes place.

  • change in state
  • change in colour
  • evolution of a gas
  • change in temperature

When a magnesium is burnt in oxygen, it gets converted to magnesium oxide.

The word-equation for the above reaction would be –
Magnesium + Oxygen → Magnesium oxide

Chemical equations can be expressed more concise and useful if we use chemical formulae instead of words.

2Mg + O2 → 2MgO

In chemical reactions, the breaking and making of bonds takes place between atoms to produce new substances.

Types of Chemical Reactions

  • Combination Reaction
  • Decomposition Reaction
  • Displacement Reaction
  • Double Displacement Reaction

Combination Reaction

A reaction in which two or more reactants combine together & form a single product is known as a combination reaction.

In Combination reactions , the formation of new bonds and this process releases a large amount of energy in the form of heat.

This is an exothermic reaction.

Example 1:

Calcium oxide(quick lime) reacts vigorously with water to produce slaked lime (calcium hydroxide) & release a large amount of heat.

CaO(s) + H2 O(l) → Ca(OH)2(aq)

Example 2:

Burning of coal

C(s) + O2(g) → CO2(g).

Example 3:

Formation of calcium oxide by the combination elements calcium and oxygen.
2Ca + O2 → 2CaO

Example 4:

Formation of water from H2(g) and O2(g)

2H2(g) + O2(g) → 2H2O(l)

Decomposition Reaction

When reactants breaks down into products on application of energy, this type reaction is known as decomposition reaction
AB + Heat à A + B. Decomposition reaction involving the absorption of heat are known as endothermic reactions.

Example 1:

Decomposition of Iron Sulphate [FeSO4]

2FeSO4(s) + Heat → Fe2O3(s) + SO2(g) + SO3(g)

When Iron Sulphate [FeSO4] is decomposed with the help of heat, it forms Iron Oxide [Fe2O3], Sulphur oxide [SO2] and Sulphur Trioxide [SO3]

Example 2:

Decomposition of Calcium Carbonate [CaCO3]Limestone

CaCO3(s) + Heat → CaO(s) + CO2(g)

When Calcium Carbonate [CaCO3] is decomposed with the help of heat, it forms Calcium Oxide [CaO], Carbon Dioxide [CO2] gas.

Example 3:

Decomposition of Lead nitrate [Pb(NO3)2]

2Pb(NO3)2(s)+ Heat → 2PbO(s) + 4NO2(g) + O2(g)

When Lead nitrate [Pb(NO3)2] is decomposed with the help of heat, it forms Lead Oxide [PbO], Nirogen Dioxide [NO2] gas & Oxygen gas(O2).

Example 4:

Decomposition of silver chloride [AgCl]

2AgCl(s) Sunlight → 2Ag(s) + Cl2(g)

When silver chloride [AgCl] is decomposed with the help of heat of sunlight, it forms Silver [Ag], chlorine [Cl2] gas.

Displacement Reaction

Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Metals and Non-metals both take part in this type of reactions.

Example 1:

Reaction of iron nails with copper sulphate solution

Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

When Iron nail [Fe] is placed in Copper Sulphate solution [CuSO4], it forms Iron Sulphate solution [FeSO4] and Copper [Cu].

Example 2:

Reaction of zinc with copper sulphate solution

Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

When Zinc [Zn] is placed in Copper Sulphate solution [CuSO4], it forms Zinc Sulphate solution [ZnSO4] and Copper [Cu].

Example 3:

Reaction of lead with copper chloride solution

Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s)

When Lead [Pb] is placed in Copper Chloride solution [CuCl2], it forms Lead Chloride solution [PbCl4] and Copper [Cu].

Example 4:

Reaction of chlorine with sodium bromide solution

Cl2(aq) + 2NaBr(aq) → 2NaCl(aq) + Br2(aq)

When Chlorine [Cl2] is placed in Sodium Bromide solution [NaBr], it forms Sodium Chloride solution [NaCl] and Bromine [Br2].

Double Displacement Reaction

Double Displacement Reaction is a type of chemical reactions in which one component each of both the reacting molecules is exchanged to form the products.

In this reaction, the cations and anions of two different compounds switch each other, which forms two different compounds.

Example 1:

Reaction of sodium sulphate [Na2SO4] and barium chloride [BaCl2]

Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)

When sodium sulphate [Na2SO4] reacts with barium chloride [BaCl2], it produces barium sulphate [BaSO4] and sodium chloride [NaCl]. Barium sulphate [BaSO4] is a precipitate [precipitate is an insoluble substance formed in a chemical reaction].

Example 2:

Reaction of silver nitrate [AgNO3] and sodium chloride [NaCl]

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO(aq)

When silver nitrate [AgNO3] reacts with sodium chloride [NaCl], it produces silver chloride [AgCl] and sodium nitrate [NaNO]. Silver chloride [AgCl] is a precipitate.


Oxidation reaction is a chemical reaction in which oxygen atom is added or hydrogen atom is removed.

Oxidation process involves loss of one or more electrons.

Note: Oxidizing agents give oxygen to another substance.

Example 1:

Reaction of Copper and Oxygen

2Cu + O2 → 2CuO

Example 2:

Reaction of Magnesium and Oxygen

2Mg + O2 → 2MgO

In the above reactions, copper and magnesium getting oxidised and these two reactions are oxidation reaction.


Reduction reaction is a chemical reaction in which oxygen atom is removed or hydrogen atom is added.

Reduction process involves gain of one or more electrons.

Note: Reducing agents remove oxygen from another substance.

Example 1:

Reaction of Copper oxide and Hydrogen

CuO + H2 → Cu + H2O

Oxygen is removed from copper and hydron is added to it in the reaction, therefore reduction occurs.

Redox Reaction

Redox reaction is a chemical reaction in which both oxidation and reduction takes place simultaneously, which means one reactant gets oxidised, the other gets reduced.

Example 1:

Reaction of Copper oxide and Hydrogen

Redox Reaction

Have You Observed The Effects Of Oxidation Reactions In Everyday Life?


Corrosion is a gradual destruction of pure metals by the action of air, moisture or a chemical (such as an acid) on their surface

    Corrosion can be prevented by the following methods

  1. Oil or Grease
  2. Painting
  3. Galvanisation
  4. Alloying
  5. Tin or Chromium plating


Rancidity is a chemical process in which food material containg fats and oils gets oxidised, and the smell and taste changes or spoiled.

    Rancidity can be prevented by the following methods

  1. Adding antioxidants
  2. Storing food in airtight containers
  3. Refrigerating food
  4. Replacing oxygen in the containers with another gas [Nitrogen]

Question & answer

Chemical Reactions and Equations MCQ Test


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