Chapter 1|| Chemical reaction and Equation || Class 12 || NCERT Exemplar Solution

                                                     Chapter - 1

Chemical Reactions and Equations

Multiple Choice Questions 

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) 

Soln: Answer is (d) Combustion of Liquefied Petroleum Gas (LPG) 

Explanation: Combustion is always a chemical change because new compound is formed after burning and it is irreversible.

2. The following reaction is an example of a 4NH3 (g) + 5O2 (g) → 4NO(g) + 6H2O(g) 

(i) displacement reaction 

(ii) combination reaction 

(iii) redox reaction 

(iv) neutralisation reaction 

(a) (i) and (iv) 

(b) (ii) and (iii) 

(c) (i) and (iii) 

(d) (iii) and (iv) 

Soln: Answer is (a) (i) and (iv) 

Explanation: The reaction provided is a mixture of displacement and redox reaction because in this reaction oxygen displace hydrogen in the ammonia. Here nitrogen is getting oxidized and oxygen is reduced.

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

3Fe(s) + 4H2O(g) → Fe3O4 (s) + 4H2 (g) 

(i) Iron metal is getting oxidised 

(ii) Water is getting reduced 

(iii) Water is acting as reducing agent 

(iv) Water is acting as oxidising agent 

(a) (i), (ii) and (iii) 

(b) (iii) and (iv) 

(c) (i), (ii) and (iv) 

(d) (ii) and (iv)

Soln: Here Oxygen combines with water to get oxidized. Oxygen is removed from water hence it is getting reduced. Water is providing oxygen and it acts as an oxidizing agent. 

4. Which of the following are exothermic processes? 

(i) Reaction of water with quick lime 

(ii) Dilution of an acid 

(iii) Evaporation of water 

(iv) Sublimation of camphor (crystals) 

(a) (i) and (ii) 

(b) (ii) and (iii) 

(c) (i) and (iv) 

(d) (iii) and (iv) 

Soln: Answer is (a) (i) and (ii) Explanation: Exothermic process are the one which release enormous amount of heat When water reacts with water and acid reacts with water it releases enormous amount of heat hence Answer is (a) (i) and (ii).

5. Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is(are) correct? 

(i) In beakers A and B, exothermic process has occurred. 

(ii) In beakers A and B, endothermic process has occurred. 

(iii) In beaker C exothermic process has occurred. 

(iv) In beaker C endothermic process has occurred. 

(a) (i) only 

(b) (ii) only 

(c) (i) and (iv) 

(d) (ii) and (iii) 

Soln: Answer is (c) (i) and (iv) 

Explanation: Exothermic processes will increase the temperature whereas exothermic processes will decrease the temperature. 

6. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation? 

(a) KMnO4 is an oxidising agent, it oxidises FeSO4 

(b) FeSO4 acts as an oxidising agent and oxidises KMnO4 

(c) The colour disappears due to dilution; no reaction is involved 

(d) KMnO4 is an unstable compound and decomposes in presence of FeSO4 to a colourless compound. 

Soln: Answer is (a) KMnO4 is an oxidising agent, it oxidises FeSO4 Explanation: In this reaction potassium permanganate is an oxidizing agent. Purple color appeared due to potassium permanganate when all the permanganate solution is utilized

7. Which among the following is(are) double displacement reaction(s)? 

(i) Pb + CuCl2 → PbCl2 + Cu 

(ii) Na2 SO4 + BaCl2 → BaSO4 + 2NaCl 

(iii) C + O2 → CO2 

(iv) CH4 + 2O2 → CO2 + 2H2O 

(a) (i) and (iv) 

(b) (ii) only 

(c) (i) and (ii) 

(d) (iii) and (iv) 

Soln: Answer is (b) (ii) only 

Explanation: Here Sodium and Barium are displaced from each other’s salts hence it is a double displacement reaction. 

8. 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 (iii) 

(d) (iv) only 

Soln: Answer is (a) (i) only 

9. 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 an 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) 

Soln: Answer is (b) (ii) and (iii) 

Explanation: When Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. It proves the reaction is exothermic . PH of the solution will be more than 7 because oxides and hydorxides of metals are alkaline. 

10. 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) (i) only 

(b) (ii) only 

(c) (iv) only 

(d) (ii) and (iv) 

Soln: Answer is (c) (iv) only 

Explanation: Ammonium and barium are getting displaced from their respective salts. Hence this is a double displacement reaction. 

11. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is 

(a) 1:1 

(b) 2:1 

(c) 4:1 

(d) 1:2 

Soln: Answer is (b) 2:1 

Explanation: 1 Mole of water has 2 moles of Hydrogen and 1 mole of water. Hence mole ration between hydrogen and oxygen is 2:1. 

12. 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) (i) and (iii) 

(b) (ii) only 

(c) (iii) only 

(d) (ii) and (iv) 

Soln: Answer is (d) (ii) and (iv) 

Explanation: Change of solid to gas or liquid to gas absorbs heat hence sublimation of dry ice and evaporation is an endothermic reaction. 

13. 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 

Soln: Answer is (b) Lead acetate 

Explanation: To get lead iodide we need a compound containing lead hence Ammonium nitrate and Potassium sulphate are ruled out. Lead sulphate is insoluble hence it cannot be used so the answer is (b) Lead acetate 

14. 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 

Soln: Answer is (d) Helium or nitrogen 

Explanation: Oxygen cannot be used as it is an oxidizing agent. Helium can be used as it is an inert gas. Nitrogen is less reactive and it is cheaper than Helium. In most cases nitrogen is used in packet to prevent rancidity. 

15. The following reaction is used for the preparation of oxygen gas in the laboratory 2 (g) 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 

Soln: Answer is (a) It is a decomposition reaction and endothermic in nature Explanation: Potassium chlorate decomposes to give potassium chloride and oxygen. This is a decomposition reaction which is endothermic in nature. 

16. 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 presence of air at high temperature 

Soln: Answer is (d) Heating copper wire in presence of air at high temperature Explanation : In first three options given here there is no involvement of chemical reaction. When copper is heated in presence of air at high temperature copper undergoes oxidation reaction to give out copper oxide. 

17. In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature? (a) 2H2 (l) + O2 (l) → 2H2O(g) (b) 2H2 (g) + O2 (l) → 2H2O(l) (c) 2H2 (g) + O2 (g) → 2H2O(l) (d) 2H2 (g) + O2 (g) → 2H2O(g) 

Soln: Answer is (c) 2H2 (g) + O2 (g) → 2H2O(l) Explanation: At room temperature hydrogen and oxygen are gases while water is liquid in nature hence option c) represents correct states of reactants and products. 

18. Which of the following are combination reactions?

(a) (i) and (iii) 

(b) (iii) and (iv) 

 (c) (ii) and (iv) 

 (d) (ii) and (iii) 

Soln: Answer is (d) (ii) and (iii) 

Explanation: Here two reactants react to form a single product hence option ii) and iii) represents combination reactions.

Short Answer 

Questions 19. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case. 

(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas. 

(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water. 

(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2 SO4 . (d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light. Soln: Chemical Reactions and Equations (a) This is an example of combination reaction. (b) NaOH (aq)+CH3COOH( ) CH3COONa(aq)+H2O( ) This is an example of neutralisation reaction between a strong base and weak acid (c) C2H5OH(aq)+CH3COOH( ) CH3COO C2H5 (aq)+H2O( ) This is an example of neutralisation reaction as double displacement reaction. (d) C2H4(g)+3O2(g) 2CO2(g) + 2H2O(g)+Heat + Light This is an example of oxidation reaction. 20. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case. (a) Thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide. (b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride. (c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine. (d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.