AKC SCIENCE CLASSES
CLASS 10 TH (CBSE AND MP BOARD)
CHAPTER 01
Chemical Reactions and Equations
NCERT TEXTBOOK EXERCISE
(PAGE 14-16)
Q:-01:- Which of the statement about the reaction below are incorrect ?
2PbO(s) + C(S) → 2Pb(s) + CO2
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised .
(c) Carbon is getting reduced.
(d) Lead oxide is getting reduced.
(ⅰ) (a) and (b)
(ⅱ) (a) and (c)
(ⅲ) (a), (b) and (c)
(ⅳ) all
Ans:- (ⅰ). ( Note :- (c) and (d) are correct. )
Q:-02:- Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) Combination reaction
(b) Double displacement reaction.
(c) Displacement reaction.
(d) displacement reaction.
Ans:- (d) Displacement reaction.
Q:-03:- What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
(a) Hydrogen gas an iron chloride are produced.
(b) Chlorine gas and hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Ans:- (a) Hydrogen gas and iron chloride are produced.
Q:-04:- What is a balanced chemical equation? Why should chemical equations be balanced?
Ans:- In a balanced equation, the number of atoms of each element on both the sides of the equation are equal. A balanced equation satisfies mass balance as well as charge balance.
The chemical equation must be balanced with respect to mass because matter can neither be created nor destroyed. The equation must be balanced with respect to charge because the electrons lost by atoms to form cations are equal to the electrons gained by other atoms to form anions.
Q:-05:- Translate the following statements into chemical equations and then balanced them:-
(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.
Ans:- (a) 3H2(g) + N2(g) → 2NH3(g)
(b) 2H2S(g) + 3O2(g) → 2SO2(g) + 2H2O(l)
(c) 3BaCl2(aq) + Al2(SO4)3(aq) → 2AlCl3(aq) + 3BaSO4(s)
(d) 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g).
Q:-06:- Balanced the following chemical equations:-
(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
Q:-07:- Write a balanced chemical equations for the following reactions:-
(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
Q:-08:- Write the balanced chemical equation for the following and identify the type of reaction in each cases.
(a) Potassium bromide (aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon diaoxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
Ans:- (a) 2KBr(aq) + BaI2(aq) → 2KI(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.
Q:-09:- What does one mean by exothermic and endothermic reactions? Give examples.
Ans:- One knows that constituent elements in a compound are bound by chemical bonds. During a chemical change, when bonds between the constituents of the reactants are broken, energy is consumed whereas energy is given out when the bonds are formed as in the case of products. Thus, depending on whether overall energy is given out or consumed, the reaction is either exothermic or endothermic.
EXOTHERMIC REACTIONS :- (a) Chemical reactions in which energy is evolved (or given out) are known as exothermic reactions. For example,
C(s) + O2(g) → CO2(g) + 393.7 KJ (△H = − 393.7 KJ)
This shows 1 mole of carbon reacts with 1 mole of oxygen and liberates 393.7 KJ Of heat.
(b) Formation of ammonia from nitrogen and hydrogen is an exothermic reaction
N2(g) + 3H2(g) → 2NH3(g) + 92 KJ (△H = - 92 KJ)
ENDOTHERMIC REACTIONS :- (a) Reactions in which energy is absorbed are called endothermic reactions. For example,
When carbon reacts with sulphur, 92KJ of heat is absorbed during the process.
C(s) + 2S(s) → CS2(l) - 92 KJ (△H = + 92 KJ).
(b) Formation of nitric oxide (NO) is an endothermic reaction
N2(g) + O2(g) → 2NO(g) - 180.5 KJ (△H = + 180.5 KJ).
SIMILAR QUESTION:-
- Differentiate between an exothermic and an endothermic reaction. Write one example for each one of these reactions in the form of balanced chemical equation.
Ans:- During digestion, food is broken down into simpler substances. Food like rice, potato and bread are made up of carbohydrates. These carbohydrates are further broken down to glucose. Glucose during respiration (inhalation of oxygen) is oxidised with the liberation of energy as shown below :-
C6H12O6(aq) + 6O2(aq) → 6O2(aq) + 6H20(l) + energy
Glucose
Thus, respiration is an exothermic process.
Q:-11:- Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Ans:- The decomposition reaction is the opposite of combination reaction.
In a decomposition reaction, a single compound breaks down to produce two or more simpler substances, e.g., mercuric oxide on heating decomposes to mercury and oxygen.
2HgO → 2Hg + O2
In a combination reaction, two or more substances simply combine to form a new substance, e.g., magnesium combines with oxygen to give magnesium oxide.
2Mg + O2 → 2MgO
SIMILAR QUESTION:-
- Differentiate between a combination reaction and a decomposition reaction. Write one chemical equation for each of these reactions.
Q:-12:- Write an equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Ans:- When energy is supply in the form of HEAT.
2MgO(s) ⟶ 2 Mg(s) + O2(g)
When energy is supply in the form of LIGHT.
AgBr(s) ⟶ Ag(s) + Br2(g)
When energy is supply in the form of ELECTRICITY AND ACID. 2H2O(l) ⟶ 2H2(g) + O2(g).
Q:-13:- What is the difference between displacement and double displacement reactions?
Ans:- In displacement reactions, a more reactive metal displaces a less reactive metal from its solution while in double decomposition reactions, two reactants in solution exchange their ions. For examples,
(ⅰ) Fe(s) + CuSO4(aq) ⟶ Cu(s) + FeSO4(aq)
This is a displacement reaction where iron displaces copper from its solution.
(ⅱ) AgNO3(aq) + NaCl(aq) ⟶ AgCl(s) + NaNO3
This is a double displacement reaction where silver nitrate and sodium chloride exchange Cl- and N03- ions between them.
Q:-14:- In the refining of silver, recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Ans:- 2AgNO3 + Cu(s) ⟶ Cu(NO3)2(aq) + 2Ag(s)
Q:-15:- What do you mean by a precipitation reaction? Explain by giving examples.
Ans:- When two reactant in solution react and one or more of the products is insoluble or forms a precipitate, the reaction is called precipitation reaction. For example, when a solution of iron chloride and ammonium hydroxide are mixed, a brown precipitate of iron hydroxide is formed.
FeCl3(aq) + 3NH4OH(aq) ⟶ 3Fe(OH)3(s) + 3NH4Cl(aq)
Ferric Ferric
Chloride hydroxide
Q:-16:- Explain the following in terms of gain or loss of oxygen with two examples each :
(a) Oxidation (b) Reduction.
Ans:- (a) Oxidation :- A chemical reaction in which a substance gains oxygen is called Oxidation.
heat
Example:- 2Cu + O2 ⟶ 2CuO, Cu is oxidised to CuO.
burn
2Mg + O2 ⟶ 2MgO, Mg is oxidised to MgO.
(b) Reduction :- A chemical reaction in which a substance loses oxygen is called Reduction.
Example:- ZnO + C ⟶ Zn + CO is reduced to Zn.
CuO + H2 ⟶ Cu + H2O, CuO is reduced to Cu.
Q:-17:- A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.
Ans:- Element 'X' = Copper (Cu)
Compound = Copper Oxide (CuO)
2Cu(s) + O2 ⟶ 2CuO
Brown (from air) Black
Q:-18:- Why do we apply paint on iron articles?
Ans:- Paint acts as antioxidant and saves iron articles from damages due to corrosion. It acts as buffer between iron articles and moist air.
Q:-19:- Oil and fat containing food items are flushed with nitrogen. WHY?
Ans:- To keep food items fresh and save these from oxidising effect of oxygen, food items are flushed with nitrogen.
Q:-20:- Explain the following terms with one example each:-
(a) Corrosion (b) Rancidity.
Ans:- (a) CORROSION:- Due to the effect of moisture and oxygen, metals get corroded, i.e., metals particularly iron from a porous layer on the surface and thus gets damaged. This effect is called Corrosion.
Corrosion causes damages to metals articles like cars bodies, bridges, iron railings, ships and other substances of daily use.
(b) RANCIDITY:- Fats and oils in food kept for long time gets oxidised and become rancid and taste of food changes and causes infection on eating. This is called Rancidity.
To prevent rancidity antioxidants (which prevent oxidation) are added to foods containing fats and oils. Rancidity can also be prevented by flushing out oxygen with an inert gas like nitrogen. For example, packets of food items like chips are flushed with nitrogen so that these can be used even after long duration.
SCIENCE || CLASS 10TH || CHAPTER 01 || PART 1 || CBSE AND MP BOARD
