Class 10 Chemical Equations and Reactions Extra Questions

TOPIC-1: Chemical Reactions and Equations

Chemical Reactions and Equations: Balanced and unbalanced chemical equations and balancing of chemical equations. 


Q.1. What is a chemical reaction? [CBSE 2011]

Ans. The process in which original substances lose their nature and identity and give new chemical substances with different properties are called chemical reactions. 

Q. 2. State one basic difference between a physical change and a chemical change. 

[CBSE 2011] 

Ans. In a physical change, no new substance is formed while a new substance is formed in a chemical change. 

Q.3. What is the chemical equation?

 Ans. The representation of a chemical reaction by using the symbols and formulae of the reactants and the product is called a chemical equation. 

Q.4. Which of the following processes represent a chemical reaction? 

(a) Grapes get fermented. (b) The lighting of an electric bulb. (c) Passing electricity through acidulated water. 

(d) Magnetising an iron bar.

 Ans. (a) Grapes get fermented and (c) Passing electricity through acidulated water are examples of chemical reactions. 

Q.5. Name and state the law which is kept in mind when we balance a chemical equation. (CBSE 2012, HOTS] 

Ans. We follow the law of “conservation of mass” while balancing a chemical

equation. The law of conservation of mass states: Matter can neither be created nor destroyed in a chemical reaction.

Q. 6. What happens chemically when quick lime is added to water? [CBSE 2008] Ans. Quick lime (calcium oxide) reacts vigorously with water to produce calcium hydroxide (slaked lime) and releases a large amount of heat. 

Q.7. When CO is passed through lime water, it turns milky, why? 

 Ans. Lime water (calcium hydroxide) combines with carbon dioxide (CO) to form a suspension of calcium carbonate (CaCO3) which makes lime water milky. 

Q.8. What happens when a magnesium ribbon is ignited? Give a chemical reaction. 

Or What happens when magnesium ribbon burns in air?

Ans. When magnesium ribbon burns in the air it gives dazzling white light and combines with oxygen to form magnesium oxide. 

2Mg(s) +0,(8) — + 2MgO(s)

Q.9. Why do we rub magnesium ribbon with sand-paper before igniting it?

 Ans. Remove the layer of oxide and carbonate from the surface of the magnesium ribbon.  

Q. 10. What do you mean by balanced chemical equation?

Ans. An equation in which the number of atoms of different elements on the two sides (LHS and RHS) of the equation are equal and are called balanced chemical equations. 

Q.11. Tell whether heat is evolved or absorbed when quick lime is added to water.  

Ans. Because the solution becomes hot. So heat has evolved. 

Q. 12. Which one is a chemical change: fermentation of fruit juice or diluting fruit juice? CBSE 2011] 

Ans. Fermentation of fruit juice is a chemical change.

 Q. 13. Name the gas evolved when zinc reacted with diluted. HCl. 

Ans. Hydrogen gas is evolved. 

Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) 1 

Q. 14. Is the burning of candle wax a physical change or a chemical change? [CBSE 2011]

Ans. The hydrocarbon of wax burns to produce CO2 and H2O. So, it is a chemical change.

Q.15. Write the equation in the symbolic form with state symbols for the following reaction: 

Zinc + Sulphuric acid —> + Zinc sulphate + Hydrogen

 Ans. Zn(s) + H2SO4(aq) —ZnSO4(aq) + H2(g)

Q.16. Balance the following chemical equation: 

Fe(s) +H2O(g) —> Fe2 O3(s) +H2(g) [CBSE 2008]

Ans. The balanced chemical equation is: 

3Fe(s) + 4H2O(l)—– ► Fe2O4(s) + 4H2(g)

Q. 17. On heating Pb (NO2), what is observed during the reaction?


Lead nitrate on heating gives lead oxide, nitrogen oxide and oxygen. Write a balanced equation with state symbols for the reaction. 

Ans. Lead nitrate [Pb (NO3)2] decomposes on strong heating with a crackling sound. It produces NO2(g), O2 (g) and PbO (s). 

2Pb (NO3)2 (s) ——Heat—-> 2PbO (s) + 4 NO2 (g) + O2(g)

Q. 18. Which colour change and smell are observed when crystals of ferrous sulphate are heated? Give chemical reactions also. [HOTS]

Ans. When crystals of ferrous sulphate are heated, the green colour of it disappears and a smell of burning sulphur is noticed. 

Q.19. On adding dilute hydrochloric acid (HCl) to copper oxide (CuO) powder, the solution formed is blue-green. Predict a new compound formed which imparts a blue-green colour to the solution. [CBSE 2008]

Ans. The compound formed is cupric chloride. It imparts a blue-green colour to the solution. 

Q. 20. If copper metal is heated over a flame it develops a coating. What is the colour and composition of the coating? [CBSE 2011]

 Ans. The black coating of copper oxide (CuO) is obtained.

Consider the two above-mentioned equations with two different kinds of arrows along with the product. What do these two different arrows indicate? [CBSE 2011] 

Ans. The upward arrow (1) indicates that the product is a gas while the downward arrow indicates that the product is precipitate (insoluble). 

Q. 22. Balance the given chemical equation: 

FeSO4 (s) —-Heat-à  Fe2O3 (s) + SO2 (g) + SO3 (g) [A.I. 2008, 2008 C] 

Ans. 2FeSO4 (s) —Heat–> , Fe2O3 (s) + SO2 (g) + SO3 (g)

 Q. 23. Rewrite the following equation after putting reaction conditions:

CO(g) + 2H2 (g) — CH3OH(l

6 CO2 (aq) + 6H20(I) —> C6H12O6(aq) + 602 (g)

 Ans. CO(g) + 2H2 (g) —– 340K—à CH3OH (l)

24. Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?

Ans. It is because the properties of water (H2O) are different from properties of its constituting elements, hydrogen (H2) and oxygen (O2).

Q.25. Hydrogen and oxygen gases are produced at the cathode and anode respectively in the electrolysis of acidulated water. What is the ratio of the volumes of hydrogen and oxygen gases? 

Ans. In the electrolysis of acidulated water, the hydrogen and oxygen gases are produced in the ratio of 2:1.

Q. 26. In the electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over other electrodes? [A.I. 2009]

 Ans. Because water contains hydrogen and oxygen in the ratio of 2:1.

Q.27. Balance the given chemical equation: [A.I. 2008 C]

 Al(s) + CuCl2 (aq) AICI2 (aq) + Cu (s)

Ans. 2Al (s) + 3CuCl2 (aq)——->2AlCl2 (aq) + 3Cu(s)

Q. 28. Write a balanced chemical equation to represent the following reaction: Carbon monoxide reacts with hydrogen gas at 340 atm to form methyl alcohol. (CBSE 2011]

Ans. CO (g) + 2H2 (g) ⇒ 340 atm–à CH3OH

 Q. 29. Write a balanced chemical equation for the reaction between sodium chloride and silver nitrate indicating the physical states of the reactants and products. [Foreign 2010]

Ans. Ag NO2(aq) + NaCl (aq) ——> AgCl (s) + NaNO3(aq)