NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations
The syllabus to learn in this chapter are writing chemical equations, balancing chemical equations, different types of chemical equations, decomposition reaction, displacement reaction, double displacement reaction, oxidation and reaction, corrosion, rancidity.
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations
Exercises solution
Question 1:
Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Answer 1: (i) (a) and (b)
(a) Lead is getting reduced.
and (b) Carbon dioxide is getting oxidised
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Question 2:
Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
Answer 2:
(d) It is an example of a displacement reaction.
Question 3:
What happens when dilute hydrochloric acid is added to iron filings? Tick the correct
answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Answer 3:
(a) Hydrogen gas and iron chloride are produced.
Fe +2HCl → FeCl2 + H2
Question 4:
What is a balanced chemical equation? Why should chemical equations be balanced?
Answer 4:
balanced chemical equation: when the number of atoms of different elements are same on both sides of a chemical equation is called balanced chemical equation.
According to the 'law of conservation of
mass' that mass can neither be created nor destroyed. Hence, in a chemical reac-
tion, the total mass of reactants should be equal to the total mass of the products. That is,
the total number of different atoms of different elements should be equal on both sides of a
chemical equation. Hence, we always balanced a chemical equation.
Question 5:
Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and
a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Answer 5:
(a) H2 + 3N2 → 2NH3
(b) 2H2S + 3O2 → 2H2O + 2SO2
(c) 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4↓
(d) 2K + 2H2O → 2KOH + H2↑
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations
Question 6:
Balance the following chemical equations.
(a) HNO3 +Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Answer 6:
(a) 2HNO3 +Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
Question 7:
Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Answer 7:
a) Ca(OH)2 + CO2 → CaCO3 + H2O
(b) Pb + CuCl2 ———-> PbCl2 + Cu
(c) BaCl2 + Na2SO4 ———> BaSO4 + 2NaCl
(d) Zn + 2AgNO3 ———–> Zn(NO3)2 + 2Ag
Question 8:
Write the balanced chemical equation for the following and identify the type of reaction
in each case.
(a)Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) +
Barium bromide(s)
(b) Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g)
(c) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen(g)
Answer 8:
(a) 2KBr (aq) + BaI2(aq) ——–> 2Kl (aq) + BaBr2(aq)
Double displacement reaction
(b) ZnCO3(s) ———-> ZnO(s) + CO2(g); Decomposition reaction
c) H2(g) + Cl2(g) ———–> 2HCl(g) Combination reaction
(d) Mg (aq) + 2HCl (aq) ———–> MgCl2(aq) + H2(g)
Displacement reaction
Question 9:
What does one mean by exothermic and endothermic reactions? Give examples.
Answer 9:
Exothermic reaction: The chemical reaction in which heat is produced is called exothermic
reaction.
Example: when water is added to calcium hydroxide heat is produced, is an example of exothermic reactionAnd adding water to concentrated sulphuric acid is another example of exothermic reaction.
Endothermic reaction: The chemical reaction in which heat is absorbed is called
endothermic reaction.
Example: The decomposition of silver bromide is an example of endothermic reaction.
2AgBr → 2Ag + Br2 - heat energy
Question 10:
Why is respiration considered an exothermic reaction? Explain.
Answer 10:
During respiration, food (that is glucose) is broken down in the presence of oxygen in the cell and energy is produced which helps to perform various activities in our life. Since it is a chemical reaction and energy is produced here, respiration is an example of an exothermic reaction process.
C6H12O6 + 6O2→ 6CO2 + 6H2O + energy.
Question 11:
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer 11:
Decomposition reactions are those in which a compound breaks down to form two or more then two products. These reactions require a source of energy to proceed. A combination reaction is a reaction in which two or more then two reactants or compounds combine to form one product. Here energy is produced.
Hence decomposition is called opposite of combination reaction.
Decomposition reaction: AB → A + B
Example: CaCO3 → CaO + CO2
Combination reaction: A +B → AB
Example: 2H2 + O2 → 2H2O
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations
Question 12:
Write one equation each for decomposition reactions where energy is supplied in the
form of heat, light or electricity.
Answer 12:
(a) Thermal decomposition reaction:
CaCO3 → CaO + CO2
(b) Decomposition by light:
2AgCl → 2Ag + Cl2↑
c) Decomposition by electricity:
2H2O → 2H2 + O2
Question 13:
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer 13:
In a displacement reaction, a more reactive element replaces a less reactive element from its compound. Whereas in a double displacement reaction, two compounds combine by an exchange of ions to form two new compounds.
For example:
Displacement reaction: The reaction between copper sulphate and zinc is an example of displacement reaction and here products forms are zinc sulphate and copper.
CuSO4 + Zn → ZnSO4 + Cu
Double displacement reaction: The reaction between barium chloride and sodium sulphate is an example of double displacement reaction and the products form are barium sulphate and sodium chloride.
BaCl2 + Na2SO4 → BaSO4 + 2NaCl
Question 14:
In the refining of silver, the recovery of silver from silver nitrate solution involved
displacement by copper metal. Write down the reaction involved.
Answer 14:
2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s)
Question 15:
What do you mean by a precipitation reaction? Explain by giving examples.
Answer 15:
A reaction in which two miscible liquid solutions react to form an insoluble solid which is separated from the solution is called precipitation reaction.
For example: When silver nitrate solution reacts with sodium chloride solution is an example of precipitation reaction where white precipitate of silver chloride is formed along with sodium nitrate.
AgNO3 + NaCl → AgCl↓ + NaNO3
Question 16:
Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Answer 16:
(a) Gaining oxygen of a substance in a chemical reaction is called oxidation.
For example:
(i) when magnesium burns in oxygen, oxidation of magnesium occurred
2Mg + O2 → 2MgO
(ii) when copper oxide reacts with hydrogen forms copper and water. Here oxygen is gained by hydrogen and it's oxidation occurs.
CuO + H2 → Cu + H2O
(b) Reduction is the loss of oxygen.
For example:
(i) when zinc oxide reacts with carbon, reduction of zinc oxide occurs and forms zinc along with carbon monoxide.
ZnO + C → Zn + CO
(ii) when ferric oxide reacts with aluminum, here reduction of ferric oxide occurs and forms iron along with aluminum oxide.
Fe2O3 + 2Al →Al2O3 + 2Fe
Question 17:
A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Answer 17:
The shiny brown-coloured element ‘X’ is copper (Cu). When shiny brown coloured copper is heated in air forms copper oxide which is black in colour.
2Cu + O2 → 2CuO
So, black coloured compound is copper oxide or copper (II) oxide.
Question 18:
Why do we apply paint on iron articles?
Answer 18:
We add paint on iron articles to prevent them from rusting by preventing direct contact with the air and moisture.
Question 19:
Oil and fat containing food items are flushed with nitrogen. Why?
Answer 19:
Nitrogen is an inert gas and does not easily react with these substances. On the other hand,oxygen reacts with food substances and makes them rancid. Thus, bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack. When oxygen is
not present inside the pack, rancidity of oil and fat containing food items is avoided.
Question 20:
Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Answer 20:
(a) Corrosion: The process in which metals are eaten up gradually by the action of air,
moisture or a chemical is called corrosion.
Rusting of iron is a common example of corrosion.
4Fe + 3O2 + nH2O → 2Fe2O3, nH2O
(b) Rancidity: The condition produced by the aerial oxidation of fats and oils in foods
marked by unpleasant smell and taste is called rancidity.
Rancidity spoils the food materials prepared by fats and oil which have been kept for a long time and makes them unfit for eating. The potato chips turn rancid and become unfit for eating.
Rancidity can be avoided by:
1. Storing food in air tight containers
2. Storing food in refrigerators
3. Adding antioxidants
4. Storing food in an environment of nitrogen
NCERT Book Intext Questions (page 6):
Question 1:
Why should a magnesium ribbon be cleaned before burning in air?
Answer 1:
Magnesium is a very reactive metal like (Na, Ca, etc.). When it expose to air it
reacts with oxygen to form a layer magnesium oxide (MgO) on its surface.
2Mg + O2 → 2MgO
This layer of magnesium oxide is quite stable and prevents further reaction of
magnesium with oxygen. The magnesium ribbon is cleaned by sand paper to
remove this layer so that the underlying metal can be used for the reaction.
Question 2:
Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium
chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
Answer 2:
(i) H2 + Cl2 → 2HCl
Hydrogen + Chlorine → Hydrogen chloride
(ii) 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3
(iii) 2Na + 2H2O → 2NaOH + H2
Question 3:
Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution
(in water) to produce sodium chloride solution and water.
Answer 3:
(𝒊). BaCl2(aq)+ Na2SO4(aq)→ BaSO4(s) + 2NaCl(aq)
(ii) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(𝑙)
NCERT Book Intext Questions of Chemical Reaction and Equations (page 10):
Question 1:
A solution of a substance ‘X’ is used for white washing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Answer 1:
(i). The substance ‘X’ is calcium oxide. Its chemical formula is CaO.
(ii). Calcium oxide reacts with water to form calcium hydroxide
CaO + H2O → Ca(OH)2
Question 2:
Why is the amount of gas collected in one of the test tubes in Activity 1.7 double
of the amount collected in the other? Name this gas.
Answer 2:
During the Electrolysis of water, hydrogen and oxygen is get separated by the
electricity.
2H2O → 2H2 + O2
Water (H2O) contains two parts hydrogen and one part oxygen. Since hydrogen goes to one test tube and oxygen goes to another, the amount of gas collected in one of the test tubes is double of the amount collected in the other.
NCERT Book Intext Questions (page 13):
Question 1:
Why does the colour of copper sulphate solution change when an iron nail is
dipped in it?
Answer 1:
Since iron is more reactive copper, iron reacts with copper sulphate to form ferrous sulphate and copper. As a result of the blue coloured copper sulphate solution gradually fades and green colour appears.
Fe + CuSO4 →FeSO4 + Cu
Question 2:
Give an example of a double displacement reaction other than the one given in Activity 1.10.
Answer 2:
Sodium carbonate reacts with calcium chloride forms calcium carbonate and
sodium chloride.
Na2CO3 + CaCl2 → CaCO3 + 2NaCl
(AB + CD → AC +BD)
In this reaction, sodium carbonate and calcium chloride exchange ions to form
two new compounds named calcium carbonate and sodium chloride. Hence, it is a double displacement reaction.
Access Solutions of Class 10 Science all chapters in PDF
Chapter 1 – Chemical reactions and equations
Chapter 3 – Metals and Non-metals
Chapter 4 – Carbon and Its Compounds
Chapter 5 – Periodic Classification Of Elements
Chapter 6 – Life Processes
Chapter 7 – Control and Coordination
Chapter 8 – How do Organisms Reproduce?
Chapter 9 – Heredity and Evolution
Chapter 10 – Light Reflection and Refraction
Chapter 11 – The Human Eye and Colourful World
Chapter 12 – Electricity
Chapter 13 – Magnetic Effects of Electric Current
Chapter 14 – Sources of Energy
Chapter 15 – Our Environment
Chapter 16 – Sustainable Management of Natural Resources
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations
Types Of Chemical Reactions
Chemical reaction: The process in which a substance (reactant) converts into a new substance (product) by forming and breaking bonds between different atoms along with releasing or absorbing energy is called chemical reaction.
Combination Reaction:
When two or more than two elements or compounds combine to form one product is called a combination reaction.
For example
• H2 + Cl2 → 2HCl
• Zn + CuSO4 → ZnSO4 + Cu
• NaOH + H2SO4 → Na2SO4 + H2O
Exothermic Reactions:
The chemical reaction in which energy is produced is called exothermic reaction.
Most of the combination reactions are exothermic in nature.
For example :
CaO + H2O → Ca(OH)2 + Heat energy
Oxidation:
The chemical reaction in which oxygen gained by a substance or hydrogen removed from a substance is called oxidation.
For example:
• 2Zn + O2 → 2ZnO
• Mn + 2HCl → MnCl2 + H2
Reduction:
The chemical reaction in which hydrogen gained by a substance or oxygen removed from a substance is called reduction reaction.
For example:
CuO + H2 → Cu + H2O
Redox Reactions:
A chemical reaction in which both oxidation and reduction takes place simultaneously is called redox reaction.
For example
CuO + H2 → Cu + H20
In this reaction copper oxide is reduced and hydrogen is oxidised.
Decomposition Reaction:
The chemical reaction in which a substance (reactant) breaks down to form two or more than two products is called decomposition reaction.
Decomposition reactions require energy either in the form of heat, light or electricity for decomposing the reactant.
For example:
CaCO3 → CaO + CO2
Endothermic Reactions:
The chemical reaction in which energy is absorbed is called endothermic reaction.
For example:
2AgBr → 2Ag + Br2 - heat energy
Displacement Reactions:
The chemical reaction in which a more reactive metal displaces a less reactive metal from its salt and forms a new salt of more reactive metal is called displacement reaction.
For Example:
Fe + CuSO4 → FeSO4 + Cu
Double Displacement Reactions:
The chemical reaction in which ions are exchanged between two reactants and form two new compounds is called double displacement reaction.
For example:
Na2CO3 + CaCl2 → CaCO3 + 2NaCl
Precipitation Reaction :
The chemical reaction in which two soluble salt solutions react to form an insoluble
compound which is stored at the bottom of the container is called precipitation reaction.
For Example
Na2SO4 + BaCl2 → 2NaCl + BaSO4↓
The topics and sub-topics in Chapter 1 Chemical Reactions and Equations
1.1 CHEMICAL EQUATIONS
1.1.1 Writing a Chemical Equation
1.1.2 Balanced Chemical Equations
1.2 TYPES OF CHEMICAL REACTIONS
1.2.1 Combination Reaction
1.2.2 Decomposition Reaction
1.2.3 Displacement Reaction
1.2.4 Double Displacement Reaction
1.3 HAVE YOU OBSERVED THE EFFECTS OF OXIDATION REACTIONS IN
EVERYDAY LIFE?
1.3.1 Corrosion
1.3.2 Rancidity.
We cover all exercises in the chapter given below:-
EXERCISE 1.1 – 3 Questions with Solutions
EXERCISE 1.2 – 2 Questions with Solutions
EXERCISE 1.3 – 3 Questions with Solutions
EXERCISE 1.4 – 20 Questions with Solutions.
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