By | April 23, 2017

Class 10

Chemical Reactions and Equations



Q1. Give some examples of reactions from your daily life that occurred around you?


  • Digestion of food
  • Respiration
  • Rusting of Iron
  • Photosynthesis
  • Cooking of Food
  • Combustion


Q2. State the changes that take place during chemical reactions?


  • Change in state
  • Change in colour
  • Evolution of a gas
  • Change in temperature
  • Change into precipitate


Q3. Write a few balanced chemical equations?


  • Zn+2HCl —-> H2 +ZnCl2
  • C + O2 —-> CO2 + Heat
  • 2C + O2 —-> 2CO
  • CH4 + 2O2 —-> CO2 + 2H2O +Heat Energy
  • 2H2 + O2 —-> 2H2O


Q4. Write the balanced chemical equations for the following?

  1. Hydrogen + Chlorine —-> Hydrogen Chloride
  2. Barium Chloride + Aluminium Sulphate —-> Barium Sulphate + Aluminium Chloride
  • Sodium + Water —-> Sodium Hydroxide +Hydrogen


  1. H2 + Cl2 —-> 2HCl
  2. 3BaCl2 + Al2(SO4)3 —-> 3BaSo4 +2AlCl3
  • 2Na + 2H2O —-> 2Na(OH) + H2


Q5. Write a balanced chemical equation for the following reaction?

  1. BaCl2 + Na2SO4 —-> BaSO4 + NaCl
  2. H2 + N2 —-> NH3
  • H2S + O2 —-> H2O + SO2
  1. HNO­3 + Ca(OH)2 —-> Ca(NO3)2 + H2O
  2. NaOH + H2SO4 —-> Na2SO4 + H2O


  1. BaCl2 + Na2SO4 —-> BaSO4 + 2NaCl
  2. 3H2 + N2 —-> 2NH3
  • 2H2S + 4O2 —-> 2H2O + 2SO2
  1. 2HNO­3 + Ca(OH)2 —-> Ca(NO3)2 + 2H2O
  2. 2NaOH + H2SO4 —-> Na2SO4 + 2H2O

Q6. Write the balanced chemical equation for the following ?

  1. Carbon Dioxide + Water —-> Glucose + Oxygen + Water
  2. Iron + Water —-> Iron Oxide + Hydrogen
  • Magnesium when burnt in air forms magnesium oxide
  1. Iron Sulphate on heating forms ferric oxide + sulphur trioxide gas + sulphur dioxide gas
  2. Silver Chloride in the presence of sunlight forms silver and chlorine gas.
  3. Iron + Copper Sulphate forms Iron Sulphate


  1. 6CO2 + 12H2O —-> C6H12O6 + 6O2 + 6H2O
  2. 3Fe + 4H2O —-> Fe3O4 + 4H2
  • 2Mg + O2 —-> 2MgO
  1. 2FeSO4 + Heat —-> Fe2O3 + SO2 + SO3
  2. 2AgCl —-> 2Ag + Cl2
  3. Fe + CuSO4 —-> FeSO4 + Cu


Q7. Differentiate between Combination Reaction and Decomposition Reaction?


             Combination Reaction            Decomposition Reaction
1)    When two or more reactants combined to form a single product then this reaction is called combination reaction. 1)    When a single reactant decompose or splits to form two or more products then this reaction is called decomposition reaction.
2)    Eg:- 2Mg + O2 —-> 2MgO

2H2 + O2 —-> 2H2O



  2)  Eg:- 2AgCl —-> 2Ag + Cl2

2FeSO4 + Heat —->  Fe2O3 + SO2 + SO3




Q8. What happens when solid iron sulphate and lead nitrate are heated strongly?


When it is  heated strongly  it decomposes into iron oxide and releases sulphur dioxide and sulphur trioxide gases.

2FeSo4 —-> Fe2O3 + So2 +So3

When lead  nitrate is heated strongly decomposes to from lead oxide and released brown coloured nitrogen dioxide gas and  oxygen gas.

2pb(No3)2  —heat–> 2Pbo +4No2 +O2(brown colour gas)

Q9. Difference  between Displacement and Double- displacement?


Displacement Double-displacement


1.     When an element displaces another element from its compound, it is a displacement reaction. When there is an exchange of atoms or icons in between two compounds it leads to a double displacement reaction.


2.     E.g: CuSo4 +Fe –>FeSo4 + Cu, CuSo4 +Zn —> ZnSo4 + Cu


e.g : BaCl2 + Na2So4 –> BaSo4 + NaCl


Q.10 What are oxidation and reduction reaction?


The reaction  in which oxygen is added or hydrogen is removed are called oxidation reaction.

2H2 + O2  —-> 2H2O

C +O2 —–> Co2

——> Reaction in which hydrogen is added on oxygen is removed are called reduction reactions.

e.g   CuO +H2  —-> Cu +H2O


Q.11 Name the substance oxidised and redused in the above reaction and also find the reducing agent and the oxidised agent?

Ans.11    Reduced :- CuO is being reduced to Cu

Oxidised :- H2 is being oxidiesed to H2O

Oxidising agent :- copper oxide

Reducing agent :- Hydrogen

Q.12 What is neutralization reaction? Give examples?

Ans.12 A reaction between an acid and a base is called neutralization reaction.

Eg: HCl + NaOH —-> NaCl + H2O

In this the acid and base neutralise each other and loose their properties by the formation of salt and water.

Q.13 What are endothermic and exothermic reactions?

Ans.13  An exothermic reaction is a type of reaction in which heat releases. Eg: When you dissolve Calcium Oxide in water heat is evolved

CaO + H2O —-> Ca(OH)2 + heat

An endothermic reaction is a type of reaction in which heat is absorbed.

Eg: CaCO3 + heat —-> CaO + CO2

Q.14 What are precipitation reactions? Give examples?

Ans.14 A reaction in which a precipitate is formed is called a precipitation reaction.

Eg: BaCl2 + Na2So4 –> BaSo4 + 2NaCl

(White ppt)

Q.15 What are balanced equations? Why should be an equation balanced?

Ans.15 A complete chemical equation represents the reactants, products and their physical states symbolically.

A chemical equation should be balanced so that the number of atoms of each type involved in a chemical reaction are same on the reactant and product sides of the equation. Equations must always be balanced.

Q.16 Why is respiration called an exothermic reactions?

Ans.16 Respiration is considered an exothermic reaction as heat is liberated during respiration.

C6H12O6 + 6O2 ­—-> 6H2O + 6CO2 + heat

Q.17 A solution of a substance ‘X’ is used for white washing.

  1. Name the substance X and write its formula?
  2. Write the reaction of the substance X with water?

Ans.17. i. ‘X’ is Ca(OH)2

  1. CaO + H2O —-> CaCO3 + heat

Q.18 Why is the amount of gas collected in one of the test tubes in Activity 1.7 (in NCERT Book) double of the amount collected in the other? Name this gas.

Ans.18  2H2O + electricity  —-> 2H2 + O2

Gas is Hydrogen

When water splits up, it gives double the amount of hydrogen than oxygen, as shown in above reaction.

Q.19 Why does the colour of Copper Sulphate solution change when an iron nail is dipped in it?

Ans.19 The colour of Copper Sulphate (CuSO4) solution changes when iron nail is dipped in it as iron displaces copper from its solution and forms iron sulphate solution which is light green in colour.

CuSO4 + Fe —-> FeSO4 + Cu

Q.20 Give an example of a double displacement reaction?

Ans. 20 BaCl2 + Na2So4 –> BaSo4 + 2NaCl

Q.21 Identify the substance that are oxidised and the substances that are reduced in following reaction?

4Na + O2 —-> 2Na2O

Ans.21 Oxidised: Sodium

Reduced: Oxygen

Q.22 Write one equation each for decomposition reactions where energy is supplied in the form of light, heat or electricity?

Ans.22 Electricity:  2H2O + electricity  —-> 2H2 + O2

Light:  2AgBr + Light —-> 2Ag + Br2

Heat:  CaCO3 + heat —-> CaO + CO2

Q.23 In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write reaction.

Ans.23 AgNO3 + Cu —-> Ag  + CuNO3

Q.24 A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name ‘X’ and black compound?

Ans.24 ‘X’ is Copper

Black Compound is CuO (Copper Oxide)

2Cu + O2 —-> 2CuO(black)

Q.25 What is corrosion? How can it be prevented?

Ans.25 Corrosion is the process of rusting of metals when they combine with oxygen, moisture and other gases in the atmosphere. This leads to their wastage. Common metals that get corroded are iron, copper, silver etc. Corrosion causes damage to car bodies, bridges, iron railings, ships and to most of metals made of iron.

  • Iron combines with oxygen of air to form rust which is iron oxide.
  • Copper combines with CO2 in air to form bluish-greenish rust which is copper carbonate.
  • Silver combines with sulphur gases in air to form a black colored coating on it which is silver sulphide.

Corrosion can be prevented by galvanization, oiling, greasing, or electroplating of the metals.


Q.26 What is Rancidity? How can it be prevented?

Ans.26 When fats and oils of the food is oxidised they change the taste and smell of the food. This is called rancidity. This can be prevented by keeping food in air tight containers or by flushing the bags of chips with nitrogen gas air by adding anti-oxidants to food. This prevents oxidation of the food.

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