CBSE Class 10 Science Chemical Reactions and Equations VBQs Set 02

Chemical equations and Types of chemical reactions

Question. Which of the following is an example of simple displacement?
(a) The electrolysis of water
(b) The burning of methane
(c) The reaction of a metal with an acid
(d) The reaction of two salt solutions to form a precipitate

Answer: (c) The reaction of a metal with an acid

Question. Which of the following is a NECESSARY condition for ALL chemical reactions?
(a) The reactants should be in the same state.
(b) Energy should be supplied to the reactants.
(c) The reactants should be at the same temperature.
(d) There should be physical contact between the reactants.

Answer: (d) There should be physical contact between the reactants.

Question. Given below is the balanced chemical equation for the thermal decomposition of lead nitrate.
\( 2Pb(NO_3)_2 \longrightarrow 2PbO + 4NO_2 + O_2 \)
Which of the following information does the coefficients of \( PbO \) and \( NO_2 \) in the equation (2 and 4 respectively) tell us?
(a) The ratio of the number of moles produced of the two substances.
(b) The ratio of the number of atoms in the two substances.
(c) The ratio of the mass produced of the two substances.
(d) The ratio of the densities of the two substances.

Answer: (a) The ratio of the number of moles produced of the two substances.

Question. Reema took 5 mL of lead nitrate solution in a beaker and added approximately 4 mL of KI solution to it. What would she observe?
(a) The solution turned red.
(b) Yellow precipitate was formed.
(c) White precipitate was formed.
(d) The reaction mixture becomes hot.

Answer: (b) Yellow precipitate was formed.

Question. A student took sodium sulphate solution in a test tube and added barium chloride solution to it. He observed that an insoluble substance has formed. The colour and molecular formula of the insoluble substance is:
(a) Grey, \( Ba_2SO_4 \)
(b) Yellow, \( Ba(SO_4)_2 \)
(c) White, \( BaSO_4 \)
(d) Pink, \( BaSO_4 \)

Answer: (c) White, \( BaSO_4 \)

Question. \( C_6H_{12}O_6(aq) + 6O_2(aq) \longrightarrow 6CO_2(aq) + 6H_2O(l) \)
The above reaction is a/an
(a) displacement reaction
(b) endothermic reaction
(c) exothermic reaction
(d) neutralisation reaction

Answer: (c) exothermic reaction

Question. It is important to balance the chemical equations to satisfy the law of conservation of mass. Which of the following statements of the law is incorrect?
(a) Total total mass of the elements present in the reactants is equal to the total mass of the elements presents in the products.
(b) The number of atoms of each element remains the same, before and after a chemical reaction.
(c) The chemical composition of the reactants is the same before and after the reaction.
(d) Mass can neither be created nor can it be destroyed in a chemical reaction.

Answer: (c) The chemical composition of the reactants is the same before and after the reaction.

Question. Which one of the following reactions is categorised as thermal decomposition reaction?
(a) \( 2H_2O(l) \longrightarrow 2H_2(g) + O_2(g) \)
(b) \( 2AgBr(s) \longrightarrow 2Ag(s) + Br_2(g) \)
(c) \( 2AgCl(s) \longrightarrow 2Ag(s) + Cl_2(g) \)
(d) \( CaCO_3(s) \longrightarrow CaO(s) + CO_2(g) \)

Answer: (d) \( CaCO_3(s) \longrightarrow CaO(s) + CO_2(g) \)

Question. \( 2HNO_3 + Ca(OH)_2 \longrightarrow Ca(NO_3)_2 + 2H_2O \); is an example of
(i) displacement reaction
(ii) double displacement reaction
(iii) neutralisation reaction
(iv) combination reaction.
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)

Answer: (b) (ii) and (iii)

Question. Burning magnesium ribbon is brought in the gas jar of carbon dioxide. Which of the following is correct ?
(i) It keeps on burning
(ii) It gets extinguished
(iii) Although \( CO_2 \) is non-supporter of combustion but burning magnesium breaks \( CO_2 \) into carbon and oxygen, oxygen helps in burning.
(iv) Carbon dioxide is supporter of combustion.
(a) (i) and (iv)
(b) (i) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)

Answer: (b) (i) and (iii)

Question. What is observed when a solution of potassium iodide is added to silver nitrate solution?
(a) No reaction takes place
(b) White precipitate of silver iodide is formed
(c) Yellow precipitate of AgI is formed
(d) AgI is soluble in water.

Answer: (c) Yellow precipitate of AgI is formed

Question. Identify ‘x’, ‘y’ and ‘z’ in the following balanced reaction
\( xPb(NO_3)_2(s) \xrightarrow{Heat} yPbO(s) + zNO_2(g) + O_2(g) \)
(a) 2, 4, 2
(b) 2, 2, 4
(c) 2, 4, 4
(d) 4, 2, 2

Answer: (b) 2, 2, 4

Question. Which of the following is precipitation as well as double displacement reaction ?
(a) \( NaOH(aq) + HNO_3(aq) \longrightarrow NaNO_3(aq) + H_2O(l) \)
(b) \( Cu(s) + 2AgNO_3(aq) \longrightarrow Cu(NO_3)_2(aq) + 2Ag(s) \)
(c) \( 2Hg(s) + O_2(g) \xrightarrow{Heat} 2HgO(s) \)
(d) \( FeCl_3(aq) + 3NH_4OH(aq) \longrightarrow Fe(OH)_3(s) + 3NH_4Cl(aq) \)

Answer: (d) \( FeCl_3(aq) + 3NH_4OH(aq) \longrightarrow Fe(OH)_3(s) + 3NH_4Cl(aq) \)

Question. Which of the following reactions will not take place?
(a) \( Zn + CuSO_4 \longrightarrow ZnSO_4 + Cu \)
(b) \( 2KBr + Cl_2 \longrightarrow KCl + Br_2 \)
(c) \( Zn + MgSO_4 \longrightarrow ZnSO_4 + Mg \)
(d) \( Mg + FeSO_4 \longrightarrow MgSO_4 + Fe \)

Answer: (c) \( Zn + MgSO_4 \longrightarrow ZnSO_4 + Mg \)

Question. When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a:
(a) Combination reaction
(b) Displacement reaction
(c) Decomposition reaction
(d) Double displacement reaction

Answer: (d) Double displacement reaction

Question. Which of the following is a thermal decomposition reaction ?
(a) \( 2H_2O \longrightarrow 2H_2 + O_2 \)
(b) \( 2AgCl \longrightarrow 2Ag + Cl_2 \)
(c) \( ZnCO_3 \longrightarrow ZnO + CO_2 \)
(d) \( H_2(g) + Cl_2(g) \longrightarrow 2HCl(g) \)

Answer: (c) \( ZnCO_3 \longrightarrow ZnO + CO_2 \)

Question. Calcium oxide reacts vigorously with water to produce slaked lime.
\( CaO(s) + H_2O(l) \longrightarrow Ca(OH)_2(aq) \)
This reaction can be classified as:
(A) Combination reaction
(B) Exothermic reaction
(C) Endothermic reaction
(D) Oxidation reaction
Which of the following is a correct option?
(a) (A) and (C)
(b) (C) and (D)
(c) (A), (C) and (D)
(d) (A) and (B)

Answer: (d) (A) and (B)

Question. In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:
(A) exchange of atoms takes place
(B) exchange of ions takes place
(C) a precipitate is produced
(D) an insoluble salt is produced
The correct option is:
(a) (B) and (D)
(b) (A) and (C)
(c) only (B)
(d) (B), (C) and (D)

Answer: (d) (B), (C) and (D)

Question. The brown gas evolved on heating of copper nitrate is
(a) \( O_2 \)
(b) \( NO_2 \)
(c) \( N_2 \)
(d) \( NO \)

Answer: (b) \( NO_2 \)

Question. Zinc reacts with silver nitrate to form which compounds?
(a) \( Zn(NO_3)_2 + Ag \)
(b) \( ZnNO_3 + Ag \)
(c) \( AgNO_3 + Zn(NO_3)_2 \)
(d) \( Ag + Zn(NO_3)_3 \)

Answer: (a) \( Zn(NO_3)_2 + Ag \)

Question. \( 2AgI(s) \xrightarrow{Sunlight} 2Ag(s) + I_2(g) \)
The colour of iodine is
(a) green
(b) purple
(c) brown
(d) pink

Answer: (b) purple

Question. On heating solid lead nitrate in a test tube, we observe
(a) fumes of yellow colour
(b) melting of lead nitrate
(c) formation of black solid
(d) fumes of brown colour

Answer: (d) fumes of brown colour

Very Short Answer Type Questions

Question. Trupti mixes an aqueous solution of sodium sulphate (\( Na_2SO_4 \)) and an aqueous solution of copper chloride (\( CuCl_2 \)). Will this lead to a double displacement reaction? Justify your answer.

Answer: There will be no reaction. Sodium sulphate and \( CuCl_2 \) will ionise in aqueous solution and will remain as ions.

Question. Match Column I with Column II.
Column I
(i) \( AgNO_3(aq) + NaCl(aq) \longrightarrow AgCl(s) + NaNO_3(aq) \)
(ii) \( H_2(g) + Cl_2(g) \longrightarrow 2HCl(g) \)
(iii) \( 2NaOH + H_2SO_4 \longrightarrow Na_2SO_4 + 2H_2O \)
(iv) \( 2Cu(NO_3)_2 \longrightarrow 2CuO + 4NO_2 + O_2 \)
Column II
(A) Neutralisation reaction
(B) Decomposition reaction
(C) Precipitation reaction
(D) Redox and combination reaction

Answer: (i) (C) (ii) (D) (iii) (A) (iv) (B)

Question. What is a balanced chemical equation?

Answer: The equation in which the number of atoms of all the molecules is equal on both sides of the equation (Reactants as well as products side) is called balanced chemical equation.

Question. Why is respiration considered an exothermic reaction?

Answer: Respiration is considered an exothermic reaction because, in respiration process, oxidation of glucose takes place which produces a large amount of heat energy, which is stored in the form of ATP. The chemical equation shown below:
\( C_6H_{12}O_6 + 6O_2 \longrightarrow 6CO_2 + 6H_2O + \text{energy} \)

Question. Balance the given chemical equations:
(a) \( Al(s) + CuCl_2(aq) \longrightarrow AlCl_3(aq) + Cu(s) \)
(b) \( FeSO_4(s) \xrightarrow{Heat} Fe_2O_3(s) + SO_2(g) + SO_3(g) \)

Answer: (a) \( 2Al(s) + 3CuCl_2(aq) \longrightarrow 2AlCl_3(aq) + 3Cu(s) \)
(b) \( 2FeSO_4(s) \xrightarrow{Heat} Fe_2O_3(s) + SO_2(g) + SO_3(g) \)

Question. (a) Balance the given chemical equation:
\( Fe(s) + H_2O(g) \longrightarrow Fe_3O_4(s) + H_2(g) \)
(b) \( AgNO_3(aq) + NaCl(aq) \longrightarrow AgCl(s) \downarrow + NaNO_3(aq) \)
\( FeS + H_2SO_4 \longrightarrow FeSO_4 + H_2S \uparrow \)
Consider the above mentioned two chemical equations with two different kinds of arrows (\( \uparrow \) and \( \downarrow \)) along with product. What do these two different arrows indicate?

Answer: (a) \( 3Fe(s) + 4H_2O(g) \longrightarrow Fe_3O_4(s) + 4H_2(g) \)
(b) \( \uparrow \) shows the gas evolved whereas \( \downarrow \) shows insoluble substance (precipitate) formed.

Question. 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?

Answer: It is because properties of compound (\( H_2O \)) are different from properties of its constituting elements i.e. \( H_2 \) and \( O_2 \).

Question. Give the chemical name of the reactants as well as the products of the following chemical equation:
\( 2HNO_3 + Ca(OH)_2 \longrightarrow Ca(NO_3)_2 + 2H_2O \)

Answer: Chemical name of reactants:
\( HNO_3 \longrightarrow \text{Nitric acid} \)
\( Ca(OH)_2 \longrightarrow \text{Calcium hydroxide} \)
Chemical name of products:
\( Ca(NO_3)_2 \longrightarrow \text{Calcium nitrate} \)
\( H_2O \longrightarrow \text{Water} \)

Question. Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.

Answer: Any two of these observations will suggest chemical reaction has taken place.
(i) Change in state.
(ii) Change in colour.
(iii) Evolution of gas.
(iv) Change in temperature.
e.g. lead nitrate is white crystalline solid, on heating gives yellowish brown solid (lead monoxide), brown gas is evolved and a colourless gas is evolved. It shows chemical reaction has taken place.
\( 2Pb(NO_3)_2(s) \xrightarrow{heat} 2PbO(s) + 4NO_2(g) + O_2(g) \)
(White) (Yellowish brown) (Brown) (Colourless)

Short Answer Type Questions

Question. Write balanced chemical equations for the following reactions:
(a) Silver bromide on exposure to sunlight decomposes into silver and bromine.
(b) Sodium metal reacts with water to form sodium hydroxide and hydrogen gas.

Answer: (a) \( 2AgBr(s) \xrightarrow{Sunlight} 2Ag(s) + Br_2(g) \)
(b) \( 2Na(s) + 2H_2O(l) \longrightarrow 2NaOH(aq) + H_2(g) \)

Question. (a) A solution of substance ‘X’ is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water.
(b) Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Answer: (a) ‘X’ is calcium oxide (\( CaO \)).
\( CaO(s) + H_2O(l) \longrightarrow Ca(OH)_2(aq) + \text{Heat} \)
(b) It is because iron displaces copper from \( CuSO_4 \) to form \( FeSO_4 \) which is pale green.
\( Fe(s) + CuSO_4(aq) \longrightarrow FeSO_4(aq) + Cu(s) \)
(Blue) (Pale green)

Question. A zinc plate was put into a solution of copper sulphate kept in a glass container. It was found that blue colour of the solution gets fader and fader with the passage of time. After a few days when zinc plate was taken out of the solution, a number of holes were observed on it.
(a) State the reason for changes observed on the zinc plate.
(b) Write the chemical equation for the reaction involved.

Answer: (a) A number of holes were observed because zinc has displaced copper from \( CuSO_4 \). Zinc metal has been used to form zinc sulphate, therefore, number of holes were observed.
(b) \( Zn(s) + CuSO_4(aq) \longrightarrow ZnSO_4(aq) + Cu(s) \)
(Blue) (Colourless)

Question. (a) What is observed when a solution of potassium iodide solution is added to a solution of lead nitrate? Name the type of reaction. Write a balanced chemical equation to represent the above chemical reaction.
(b) Why copper can displace silver from silver nitrate and silver cannot displace copper from copper sulphate solution?

Answer: (a) Yellow precipitate of lead iodide is formed. It is precipitation reaction. It is also called double displacement reaction.
\( Pb(NO_3)_2(aq) + 2KI(aq) \longrightarrow PbI_2(s) + 2KNO_3(aq) \)
(b) Copper can displace silver from \( AgNO_3 \) because copper is more reactive than \( Ag \), e.g.
\( Cu + 2AgNO_3(aq) \longrightarrow Cu(NO_3)_2(aq) + 2Ag(s) \)
Silver cannot displace copper from \( CuSO_4 \) because silver is less reactive than \( Cu \).

Question. Identify the following changes as chemical or physical.
(a) Crumpling a sheet of aluminium foil.
(b) Baking a cake.
(c) Shredding paper.
(d) Sublimation of dry ice.
(e) Changing colour and properties.
(f) Burning of paper.

Answer: (a) Physical change. (b) Chemical change. (c) Physical change. (d) Physical change. (e) Chemical change. (f) Chemical change.

Question. Write the chemical equation of the reaction in which the following changes have taken place with an example of each:
(a) change in colour.
(b) change in temperature.
(c) formation of precipitate.

Answer: (a) \( Cu(s) + 2AgNO_3(aq) \longrightarrow Cu(NO_3)_2(aq) + 2Ag \)
The solution will become blue in colour and shiny silver metal will be deposited.
(b) \( NaOH + HCl \longrightarrow NaCl + H_2O + \text{Heat} \)
The temperature will increase because heat will be evolved.
(c) \( Pb(NO_3)_2(aq) + 2KI(aq) \longrightarrow PbI_2(s) + 2KNO_3(aq) \)
(Yellow ppt.)
Yellow precipitate of \( PbI_2 \) will be formed.

Question. What is meant by skeletal type chemical equation? What does it represent? Using the equation for electrolytic decomposition of water, differentiate between a skeletal chemical equation and a balanced chemical equation.

Answer: The equations in which gaseous are written in atomic form instead of molecular form and equation is not balanced are called skeletal type of chemical equations. They represent gaseous elements formed in atomic state and equation is not balanced.
\( H_2O \xrightarrow{\text{electrolysis}} H + O \) (Skeletal equation)
Hydrogen and oxygen are written in atomic forms and equation is not balanced.
\( 2H_2O \longrightarrow 2H_2 + O_2 \) (Balanced chemical equation)
\( H_2O \longrightarrow H_2 + O_2 \) is also skeletal equation.

Question. (a) Which of the following reactions is/are an endothermic reaction(s) where decomposition also happens?
• Respiration
• Heating of lead nitrate
• Decomposition of organic matter
• Electrolysis of acidified water
(b) Silver chloride when kept in the open turns grey. Illustrate this with a balanced chemical equation.

Answer: (a) Heating of lead nitrate; and electrolysis of acidified water.
(b) \( 2AgCl(s) \xrightarrow{Sunlight} 2Ag(s) + Cl_2(g) \)

Question. Write chemical equation for the reactions taking place when
(a) Iron reacts with steam.
(b) Magnesium reacts with dil. HCl.
(c) Copper is heated in air.

Answer: (a) \( 3Fe(s) + 4H_2O(g) \longrightarrow Fe_3O_4(s) + 4H_2(g) \)
(b) \( Mg + 2HCl \longrightarrow MgCl_2 + H_2 \)
(c) \( 2Cu + O_2 \xrightarrow{heat} 2CuO(s) \)

Question. Write balanced equations for the following, mentioning the type of reaction involved.
(a) Aluminium + Bromine \(\longrightarrow\) Aluminium bromide
(b) Calcium carbonate \(\longrightarrow\) Calcium oxide + Carbon dioxide
(c) Silver chloride \(\longrightarrow\) Silver + Chlorine

Answer: (a) \( 2Al(s) + 3Br_2(g) \longrightarrow 2AlBr_3(s) \)
(b) \( CaCO_3(s) \longrightarrow CaO(s) + CO_2(g) \)
(c) \( 2AgCl(s) \xrightarrow{Sunlight} 2Ag(s) + Cl_2(g) \)

Question. 2 g of ferrous sulphate crystals are heated in a dry boiling tube.
(a) List any two observations.
(b) Name the type of chemical reaction taking place.
(c) Write the chemical equation for the reaction.

Answer: (a) (i) Green colour of \( FeSO_4 \) disappears and reddish brown \( Fe_2O_3 \) is formed.
(ii) Smell of burning sulphur.
(b) Decomposition reaction.
(c) \( 2FeSO_4(s) \xrightarrow{heat} Fe_2O_3(s) + SO_2(g) + SO_3(g) \)

Question. (a) \( A + BC \longrightarrow AC + B \)
(b) \( AB + CD \longrightarrow AC + BD \)
Identify the types of reaction mentioned above in (a) and (b). Give one example for each type in the form of a balanced chemical equation.

Answer: (a) Displacement -
• \( Fe(s) + CuSO_4(aq) \longrightarrow FeSO_4(aq) + Cu(s) \)
• \( Zn(s) + CuSO_4(aq) \longrightarrow ZnSO_4(aq) + Cu(s) \)
• \( Pb(s) + CuCl_2(aq) \longrightarrow PbCl_2(aq) + Cu(s) \)
(b) Double displacement
\( Na_2SO_4(aq) + BaCl_2(aq) \longrightarrow BaSO_4(s) + 2NaCl(aq) \)

Long Answer Type Questions

Question. A metal nitrate ‘A’ on heating gives yellowish brown coloured metal oxide along with brown gas ‘B’ and a colourless gas ‘C’. Aqueous solution of ‘A’ on reaction with potassium iodide forms a yellow precipitate of compound ‘D’. Identify ‘A, B, C, D’. Also identify the types of both the reactions. Metal present in ‘A’ is used in alloy which is used for soldering purposes.

Answer: Metal nitrate ‘A’ is \( Pb(NO_3)_2 \).
\( 2Pb(NO_3)_2(s) \xrightarrow{Heat} 2PbO(s) + 4NO_2(g) + O_2(g) \) ...(i)
(Lead nitrate 'A') (Lead (II) oxide Yellowish brown) (Nitrogen dioxide 'B' Brown) (Oxygen 'C' Colourless)
\( Pb(NO_3)_2(aq) + 2KI(aq) \longrightarrow PbI_2(s) + 2KNO_3(aq) \) ...(ii)
('A') (Potassium iodide) (Lead iodide 'D' Yellow ppt.) (Potassium nitrate)
‘A’ is lead nitrate, ‘B’ is nitrogen dioxide, ‘C’ is oxygen and ‘D’ is lead iodide.
(i) Is decomposition reaction and (ii) Is double displacement reaction (Precipitation reaction).

Question. (a) Write chemical equations for the following and balance them.
(i) Zinc carbonate(s) \(\longrightarrow\) Zinc oxide + Carbon dioxide
(ii) Potassium bromide (aq) + Barium iodide (aq) \(\longrightarrow\) Potassium iodide + Barium bromide
(iii) Nitrogen + Hydrogen \(\longrightarrow\) Ammonia.
(b) What happens when electricity is passed through acidified water?

Answer: (a) (i) \( ZnCO_3(s) \xrightarrow{Heat} ZnO(s) + CO_2(g) \)
(ii) \( 2KBr(aq) + BaI_2(aq) \longrightarrow BaBr_2(aq) + 2KI(aq) \)
(iii) \( N_2(g) + 3H_2(g) \longrightarrow 2NH_3(g) \)
(b) \( H_2 \) gas is formed at cathode and \( O_2 \) gas at anode.