Chemical Reactions and Equations

Chemical Reactions and Equations|Multiple Choice Questions (MCQs)|NCERT Solutions

Question 1. Which of the following is not a physical change?
(a) Boiling of water to give water vapour
(b) Melting of ice to give water
(c) Dissolution of salt in water
(d) Combustion of Liquefied Petroleum Gas (LPG)
Answer: (d)
Explanation: Combustion of any substance is a chemical change because new substance is formed after combustion.

Question 2. Which of the following are exothermic processes?
1. Reaction of water with quick lime
2. Dilution of an acid
3. Evaporation of water
4. Sublimation of camphor (crystals)
(a) 1 and 2
(b) 2 and 3
(c) 1 and 4
(d) 3 and 4
Answer: (a)
Explanation: Energy is released in exothermic reactions in the form of heat.

Question 3. Which among the following statement(s) is /are true?
Exposure of silver chloride to sunlight for a long duration turns grey due to
(i) The formation of silver by decomposition of silver chloride.
(ii) Sublimation of silver chloride.
(iii) Decomposition of chlorine gas from silver chloride.
(iv) Oxidation of silver chloride.
(a) (i) Only
(b) (i) and (iii)
(c) (ii) and (ii)
(d) Only (iv)
Answer : (a)
Explanation: In the presence of sunlight, AgCl decompose to form grayish white silver metal and releases chlorine gas.

Question 4. Which of the following is (are) an endothermic process(es)?
(i) Dilution of sulphuric acid
(ii) Sublimation of dry ice
(iii) Condensation of water vapours
(iv) Evaporation of water
(a) Both (i) and (iii)
(b) Only (ii)
(c) Only (iii)
(d) Both (ii) and (iv)
Answer : (d)
Explanation: An endothermic process involves absorption of heat such as
sublimation and evaporation needs heat energy.

Chemical Reactions and Equations

Question 5. In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?
(a) Lead sulphate (insoluble)
(b) Lead acetate
(c) Ammonium nitrate
(d) Potassium sulphate
Answer: (b)
Explanation: For the formation of lead iodide some soluble salt of lead is required like lead acetate which will form lead iodide with potassium acetate.

Question 6. Which of the following gases can be used for storage of fresh sample of an oil for a long time?
(a) Carbon dioxide or oxygen
(b) Nitrogen or oxygen
(c) Carbon dioxide or helium
(d) Helium or nitrogen
Answer : (d)
Explanation: Inert gases like Helium and Nitrogen can be used for storage of food items as they prevent the oxidation of food items.

Also Read: Heat and Thermodynamics

Chemical Reactions and Equations

Question 7. The following reaction is used for the preparation of oxygen gas in the laboratory

Which of the following statement(s) is/are correct about the reaction?
(a) It is a decomposition reaction and endothermic in nature
(b) It is a combination reaction
(c) It is a decomposition reaction and accompanied by release of heat
(d)It is a photochemical decomposition reaction and exothermic in nature. Answer: a
Explanation: Decomposition reaction can be defined as the reaction which involves decomposition of one compound to more than one substance. Endothermic
reactions require heat energy to form products.

Question 8.Which one of the following processes involve chemical reactions?

(a) Storing of oxygen gas under pressure in a gas cylinder
(b) Liquefaction of air
(c) Keeping petrol in a China dish in the open
(d) Heating copper wire in the presence of air at high temperature

Answer. (d)
Explanation: Chemical changes involve formation of new compounds from one of more substances. Reaction of copper wire with oxygen forms copper (ii) oxide.

Question 9. In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?

Answer: C

Explanation: At standard conditions, hydrogen and oxygen exist in gaseous state whereas water in liquid state.

Chemical Reactions and Equations

Question 10. Which of the following are combination reactions?

Chemical Reactions and Equations

(a) Both (i) and (iii)
(b) Both (iii) and (iv)
(c) Both (ii) and (iv)
(d) Both (ii) and (iii)
Answer: (d)
Explanation: Combination reactions form a new product with the combination of more than one reactant molecules.

Question 11. Solid calcium Oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime.Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is are true about slaking of lime and the solution formed?
(i) It is an endothermic reaction.
(ii) It is exothermic reaction.
(iii) The pH of the resulting solution will be more than seven.
(iv) The pH of the resulting solution will be less than seven.
(a)( i) and (ii)
(b) (ii) and (iii)
(c) (i)and (iv)
(d) (iii) and (iv)
Answer: (b)
Explanation: The formation of calcium hydroxide from calcium oxide and water with heat so it is an exothermic reaction. Calcium hydroxide is a basic compound so pH will be more than 7.

Question 12. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?

(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction

(a) Only (i)
(b) Only (ii)
(c) Only (ii)
(d) (ii) and (iv)

Answer: (d)

Explanation: Double displacement reaction involves displacement of cation and anions of two different compounds. In given reaction, precipitate of barium sulphate is formed.

Question 13. Which of the following statements about the given reaction are correct?

1. Iron metal is getting oxidized.
2. Water is getting reduced.
3. Water is acting as reducing agent.
4. Water is acting as oxidizing agent.
(a) 1,2 and 3
(b) 3 and 4
(c) 1,2 and 4
(d) 2 and 4
Answer: (c)
Explanation: Oxygen is being added to iron, hence iron is getting oxidized. Oxygen is removed from water, hence water is getting reduced. Water is providing oxygen; hence water is the oxidizing agent.

Question 14. The following reaction is an example of a

1. Displacement reaction
2. Combination reaction
3. Redox reaction
4. Neutralisation reaction
(a) 1 and 4
(b) 2 and 3
(c) 1 and 3
(d) 3 and 4

Answer: (c)
Explanation: In this reaction, oxygen is displacing hydrogen from ammonia; hence it is a displacement reaction. Moreover, nitrogen is getting oxidized and oxygen is getting reduced. Hence, this is redox reaction.