Chemical Reactions And Equations NCERT Science Class 10 lesson 1 Question And Answer
Chemical Reactions And Equations
Exercise1. Which of the statements about the reactions below is incorrect?
2PbO(s) + C(s) = 2Pb(s) + CO2(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
i. a and b
ii. a and c
iii. a, b and c
iv. all
Answer:
i. a and b
i. a and b
2. Fe2O3 + 2Al = Al2O3 + 2Fe
The above reaction is example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
Answer:
(d) displacement reaction
3. What happens when dilute hydrochloric acid is added in iron fillings?
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Answer:
(a) Hydrogen has and iron chloride are produced.
4. What is a balanced chemical equation? Why should chemical equations be balanced?
Answer:
Balance chemical equation is a equation in which number of atom of each element remains same, before and after the chemical reaction.
The law of conservation of mass states that mass can neither be created nor be destroyed in a chemical reaction. That is, the total mass of the element present in the products of chemical reaction has to be equal to the total mass of the element present in the reactants
5. Translate the following statements into chemical equations and then balance 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.
Answer:
a) H2 + N2 --> 2NH3
b) 2H2S + 3O2 --> 2H2O + 2SO2
c) 3BaCl2 + Al2(SO4)3 --> 2AlCl3 + 3BaSO4
d) 2K + 2H2O --> 2KOH + H2
6. Balance 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
Answer:
(a) 2HNO3 + Ca(OH)2 --> ca(NO3)+2H2O
(b) 2NaOH + H2SO4 --> Na2SO4+2H2O
(c) NaCl + AgNO3 --> AgCl + NaNO3
(d) BaCI + H2SO4 --> BaSO4+2HCl
7. Write the 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
Answer:
(a) Ca(OH)2 + CO2 --> CaCO3 + H2O .
(b) Zn + 2AgNO --> Zn(NO3)2 + 2Ag.
(c) 2AI + 3CuCl2 --> 2AlCl + 3Cu.
(d) BaCl2 + k2SO4 --> BaSO4 + 2KCl.
8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide(aq) + Barium iodide(aq) = Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) = Zinc(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) = Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(g) = magnesium chloride(aq) + Hydrogen(g)
Answer:
(a) 2KBr(ag) + Bal2(ag) -> 2KCl(ag) + BaBr2(s) : Double displacement reaction.
(b) ZnCO3(s) -> ZnO(s) + CO2(g) : Decomposition reaction.
(c) H2(g)+ Cl2(g) -> 2HCl(g) : Combination reaction.
(d) Mg(s)+2HCI(ag) -> MgCl2(ag)+ H2(g) : Displacement reaction.
9. What does one mean by exothermic and endothermic reactions? Give examples.
Answer:
Exothermic Reaction
Reactions in which heat is released along with the formation of products are called exothermic chemical reaction.
CH4 + 2O2 ---> CO2 + 2H2O
Endothermic Reaction
The reactions in which energy is absorbed are known are endothermic reactions.
2AgCl --> 2Ag + Cl2
10. Why is respiration considered and exothermic reaction? Explain.
Answer:
Respiration is considered as exothermic reaction because when we breathe in air in our lungs at the time of exchange of gases heat is also released and distributed throughout the body as energy.
11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer:
Decomposition reaction is called the opposite of combination reaction because, in combination reaction the product is formed from two or more reactants. And in decomposition product is formed from single reactant.
Decomposition reaction example:
2FeSO4 + --> Fe2O3 + SO2 + SO3
Combination reaction example:
CaO + H2O --> Ca(OH)2 + heat
12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Answer:
Decomposition reaction where energy is supplied in form of heat
2FeSO4 ----> Fe2O3 + SO2 + SO3Decomposition reaction where energy is supplied in form of light
2AgCl --> 2Ag + Cl213. What is the difference between displacement reaction and double displacement reaction? Write equations for these reactions.
Answer:
Displacement Reaction
Fe + CuSO4 -> FeSO4 + Cu
In this reaction, iron has displaced or removed another element copper, from copper sulphate solution. This reaction is known as displacement reaction.
Double Displacement Reaction
Na2SO4 + BaCl2 -> BaSO4 + 2NaCl
In this reaction White precipitate is formed by the reaction of SO42- and Ba2+. The other product is sodium chloride which remains in the solution. Such reaction is which there is an exchange of ions between the reactant are called double displacement reaction.
14. In the refining of silver, the recovery of silver from the silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Answer:
Cu + AgNO3 -> CuNO3 + Ag
15. What do you mean by a precipitation reaction? Explain by giving examples.
Answer:
Any reaction that produces a precipitate can be called a precipitation reaction.
Na2SO4 + BaCl2 -> BaSO4 + 2NaCl
16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Answer:
(a) Oxidation
A reaction in which substance gains oxygen or loses hydrogen is said to be oxidation.
Example:
i. CuO + H2 --> Cu + H2O
ii. 2Cu + O2 --> 2CuO
(b) Reduction
A reaction in which substance gains hydrogen or loses oxygen is said to be reduction.
Example:
i. ZnO + C --> Zn + CO
ii. Fe2O3 + 3CO --> 2Fe + 3CO2
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.
Answer:
The element X here is copper and the black coloured compound is copper oxide.
The element X here is copper and the black coloured compound is copper oxide.
18. Why do we apply paint on iron articles?
Answer:
We apply paint on iron articles because, iron articles start rusting as they come in contact with the surrounding air, moisture or water. Applying a layer of paint prevents it from coming in direct contact with the surrounding. Hence, preventing it from rusting.
19. Oil and fat containing food items are flushed with nitrogen. Why?
Answer:
Oil and fat containing food items are flushed with nitrogen gas to prevent the food items from getting oxidised.
Oil and fat containing food items are flushed with nitrogen gas to prevent the food items from getting oxidised.
20. Explain the following terms with one example each.
a) Corrosion
b) Rancidity
Answer:
a) Corrosion
When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.
The black coating on silver and the green coating on copper are the examples of corrosion.
b) Rancidity
When fats and oils in the food materials are oxidised, they become rancid and their smell and taste changes.
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