NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations
NCERT Intext Questions
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
(ii) 3 BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3
(iii) 2Na + 2H2O → 2NaOH + H2 ↑
(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.
(ii) NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
2H2O(l) → 2H2(g) + O2
Water contains 2 part of hydrogen and one part of oxygen. Therefore during the electrolysis of water the amount of hydrogen gas collected in one test tube is double than the amount of oxygen collected in other test tube.
Hence, the name of gas is hydrogen.

Na2CO3(aq) + CaCl2(aq) → CaCO3(aq) + 2NaCl(aq)
(i) 4Na(s) + O2(g) → 2Na2O(s)
(ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
(ii) In this reaction Hydrogen gains oxygen to form water. Hence H2 is being oxidised and CuO losses oxygen, so reduced.
NCERT Exercise Questions
2 PbO(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
Explanation: In the reaction C (carbon) is gaining oxygen thus it is getting oxidised and PbO (lead oxide) is losing oxygen thus it is reduced.
The above reaction is an example of a:
(a) combination reaction
(b) double displacement reaction
(c) decomposition reaction
(d) displacement reaction
Explanation: In this reaction Al is more reactive than Fe, and it displaces Fe to form Al2O3. So it is an example of displacement reaction.
(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.
Fe + 2HCl → FeCl2 + H2↑
Ans. A balanced chemical equation is the one which has number of atoms of different elements in the reactants equals to the total number of atoms of different elements in the product.
Example: 2H2O → 2H2 + O2
On reactant side — H-atom = 2 × 2 = 4, O-atom = 2
On product side — H-atom = 2 × 2 = 4, O-atom = 2
Hence it is a balanced chemical reaction.
The chemical equations should be
balanced to satisfy the law of conservation of mass.
(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.
By balancing the above equation we can get
3H2(g) + N2(g) → 2NH3(g)
(b) H2S(g) + O2(g) → H2O(l) + SO2(g)
On balancing the equation: 2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
(c) BaCl2(aq) + Al2(SO4)3(aq) → AlCl3(aq) + BaSO4(s)
On balancing the equation:
3BaCl2(aq) + Al2(SO4)3(aq) → 21AlCl3(aq) + 3BaSO4(s)
(d) K(s) + H2O(l) → KOH(aq) + H2(g)
On balancing the equation:
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
(a) HNO3 + Ca (OH)2 → Ca (NO3)2 + H2O
(b)NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Ans. (a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c)NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
(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
Ans. (a) Ca (OH)2 + CO2 → CaCO3 + H2O
(b) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
(c) 2Al + 3CuCl2 → 2AlCl3 + 3Cu
(d) BaCl2 + K2SO4 → BaSO4 + 2KCl
(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) + Chloride (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)
Ans. (a) 2KBr (aq) + Bal2 (aq) → 2Kl (aq) + BaBr2 (s)
Type: Double displacement reaction
(b) ZnCO3 (s) → ZnO (s) + CO2 (g)
Type: Decomposition reaction
(c) H2 (g) + Cl2 (g) → 2HCl (g)
Type: Combination reaction
(d) Mg(s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
Type: Displacement reaction
Ans. Exothermic reaction: When in a chemical reaction energy is released in the form of heat, the reaction is called exothermic reaction.
Example: C (g) + O2 (g) → CO2 (g)
Endothermic reaction: When in a chemical reaction energy is absorbed in the form of heat, the reaction is called endothermic reaction.
$$ \text{Example: } CaCO_3\space \xrightarrow{Heat} \text{CaO +} CO_2↑$$
Ans. Respiration is an exothermic process because during respiration glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy.
$$ \underset{\text{ Glucose}}{C_6H_{12}O_6 (aq)} + 6O_2 (g) + 6CO_2 (g) → 6H_2O (l) + Energy$$
Ans. In a decomposition reaction, a single compound breaks down to produce two or more substances whereas in combination reaction two or more substances combine to form new compound. Hence both are opposite to each other.
$$ \text{Example: } 2H_2O(l) \xrightleftarrows[Combination]{Decomposition} 2H_2(g) + O_2(g)$$
Ans. $$\underset{\text{Calcium carbonate}}{CaCO_3(s)}\xrightarrow{Heat}CaO(s) + CO_2(g) \\ \underset{\text{Silver bromide}}{2AgBr(s)} \xrightarrow{Heat} 2Ag(s) + Br_2(g) \\ \underset{\text{Water}}{2H_2O(l)} \xrightarrow{Electricity} \space 2H_2(g) + O_2(g)$$
13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Ans. In displacement reactions, a more reactive metal displaces a less reactive metal from its solution.
For example, Fe (s) + CuSO4 (aq) → Cu (s) + FeSO4 (aq)
This is a displacement reaction where iron displaces copper from its solution. In double displacement reactions, two reactants in solution exchange their ions to form new compounds. For example,
AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)
This is a double displacement reaction where silver nitrate and sodium chloride exchange Cl– and NO3– ions between them to form AgCl and NaNO3.
Ans. The reaction involve is displacement reaction. In this reaction Cu replaces Ag from its solution.
$$\underset{\text{Silver nitrate}}{2AgNO_3(aq)}+ \underset{\text{Copper}}{Cu(s)}\rightarrow \underset{\text{Copper nitrate}}{Cu(NO_3)_2} + \underset{{Silver}}{2Ag(s)} $$
Ans. A chemical reaction, in which an insoluble solid is formed from the solution. The solid formed is called precipitate and reaction is known as precipitation reaction.
$$Example: Na_2CO_3 (aq) + CaCl_{2} (aq) → \underset{{precipitate}}{CaCO_3 (s)} + 2NaCl (aq)$$
(a) Oxidation
(b) Reduction.
Ans. (a) Oxidation: The addition of oxygen to a substance is called oxidation.
Example:
(i) S(s) + O2 (g) → SO2 (g)
(Addition of oxygen to sulphur)
(ii) 2Mg(s) + O2 (g) → 2MgO (s)
(Addition of oxygen to magnesium)
(b) Reduction: The removal of oxygen from a substance is called reduction.
Example:
(i) CuO + H2 Heat → Cu + H2O
Here, copper oxide is being reduced to copper because oxygen gets removed from copper oxide.
(ii) ZnO + C → Zn + CO
Here, zinc oxide is being reduced to zinc because oxygen gets removed from zinc oxide.
Ans. The shiny elements are metal. The metal with brown colour is Cu so the element X is copper (Cu).
When copper reacts with oxygen it forms a black coloured compound, copper oxide.
$$\underset{\text{Copper (Brown)}}{2Cu} + \underset{\text{Oxygen}}{O_2} \rightarrow \underset{\text{Copper Oxide (Black)}}{2CuO}$$
Ans. Paint is applied on iron to prevent rusting which is caused by the oxygen and moisture present in air. Paint acts as a barrier and does not allow oxygen and moisture present in air to react with iron, hence saves iron from rusting.
Ans. To keep food items fresh and save from getting oxidised, food items are flushed with nitrogen because nitrogen is a non-reactive gas that does not combine with oil and fats.
Ans. (a) Corrosion : It is the process in which metals are eaten up gradually by the action of air, moisture or a chemical (such as an acid) on their surface.
Example: When iron is exposed to moist air for a long period of time, its surface acquires a coating of a brown, flaky substance called rust. Rust is mainly hydrated iron (III) oxide [Fe2O3.xH2O].
$$4Fe + 3O_2 + 2x H_2O → \underset{\text{Hydrated iron (III) oxide (Rust)}}{2Fe_2O_3.xH_2O}$$
(b) Rancidity: The process of oxidation of fats and oils which can be noticed by change in colour, smell and taste is known as rancidity.
Example: When butter is kept in open atmosphere then its smell and taste changes which results in rancidity.