KSEEB Solutions for Class 8 Science Chapter 11 Chemical Reactions and their Types

Students can Download Science Chapter 11 Chemical Reactions and their Types Questions and Answers, Notes Pdf, KSEEB Solutions for Class 8 Science helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.

Karnataka State Syllabus Class 8 Science Chapter 11 Chemical Reactions and their Types

KSEEB Class 8 Science Chemical Reactions and their Types Textbook Exercise Questions and Answers

I. Four alternatives are given to each of the following incomplete statements/questions. Choose the right answer.

Question 1.
Balancing of equations is based on
(a) Avogadro number
(b) Principle of conservation of momentum
(c) conditions for a chemical reaction to take place
(d) Law of conservation of mass or matter
Answer:
(d) Law of conservation of mass or matter

Question 2.
Identify the balanced equation in the following
(a) Si O₂ + Mg → Si + Mg O
(b) Si O₂ + 2 Mg → Si + 2 Mg O
(c) Si O + Mg → Si + Mg O₂
(d) Si O₂ + Mg → Si O + 2 Mg O
Answer:
(b) Si O₂ + 2 Mg → Si + 2 Mg O

Question 3.
The correct statement about chemical displacement is
(a) less reactive element displaces more reactive element.
(b) a non-metal displaces more reactive non-metal.
(c) more reactive element displaces less reactive element.
(d) evolution of heat when carbon is burnt in air.
Answer:
(c) more reactive element displaces less reactive element.

Question 4.
Dissolving of sugar in water is not an example for chemical reaction because
(a) there is no change in energy
(b) sufficient heat is not produced
(c) no new substances are formed
(d) no gases are evolved
Answer:
(c) no new substances are formed

Question 5.
Which of the following represents a combination of two compounds forming another compound?
(a) 2SO₂ + O₂ → 2SO₃
(b) CaCO₃ → CaO + CO₂ ↑
(c) H₂O + SO₂ → H₂SO₃
(d) 2Na + 2H₂O → 2NaOH + H₂↑
Answer:
(c) H₂O + SO₂ → H₂SO₃

II. Balance the following reactions.

Question:
1. Cu + H₂SO₄ → CuSO₄ + SO₂ + H₂O
2. Fe + H₂O → Fe₃O₄ + H₂
3. CH₄ + O₂ → CO₂ + H₂O
Answer:
1. Cu + 2 H₂SO₄ → CuSO₄ + SO₂ + 2H₂O
2. 3 Fe + 4 H₂O → Fe₃ O₄ + 4H₂
3. CH₄ + 2O₂ → CO₂ + 2H₂O

III. Answer the following:

Question 1.
Write any three differences b/w physical changes and chemical changes
Answer:
The three differences b/w physical change and chemical change areas follower Physical change chemical change Physical change Chemical change

Physical change	Chemical change
A physical change is reversible	A chemical change is not reversible
A physical change is a change in which no new substance is formed	A chemical change results in the formation of one or more new substances
Composition of the substance does not change	Composition of the substance changes

Question 2.
Group the following into physical change or chemical change
1. Dissolving salt in H₂O → chemical change
2. Burning of a fuel → chemical change
3. Rusting of iron → chemical change
4. Melting of ice cube → physical change
3. Mention one example each for the different types of chemical reactions.
Answer:
Chemical Combination:-
N₂ + 3H₂ → 2 NH₃
Chemical decomposition:
2 Hg O → 2 Hg + O₂
Chemical displacement:
Cu SO₄ + Fe → Fe SO₄ + Cu
Chemical double displacement:
CaCl₂ + Na₂CO₃ → CaCO₃ + 2 NaCI

Question 4.
Classify the following into combination, decomposition, displacement and double displacement reaction.
(a) Ca CO₃ → CaO + CO₂↑
(b) 2 Ag NO₃ + Cu → Ca (NO₃)₃ + 2 Ag↓
(c) 2 SO₂ + O₂ → 2 SO₃
(d) Na Cl + Ag NO₃ → Ag Cl + Na NO₃↓
Answer:
(a) Chemical decomposition
(b) Chemical displacement
(c) Chemical combination
(d) Chemical double displacement

Question 5.
Write the advantages of writing a chemical equation using formulas and symbols.
Answer:
The chemical equation using formulas and symbols is as follows.

1. Chemical symbols are simply written references to chemical names whose full titles can be extremely lengthy.
2. The symbols are used so that they could be understood by the whole world because the names of the mass of the chemical differ across the world, but the symbols do not.

Question 6.
During winter so many plant leaves fall on earth. But it will not cause pollution. Plastic papers that are strewn on earth cause pollution. Name the type of chemical reaction associated with this observation.
Answer:
The type of reaction observed here is chemical decomposition. The leaves that fall on the earth during the winter season get decomposed. The carbohydrates (starch) present in the leaves are decomposed into simple sugars that can be absorbed by the plants, whereas plastics are not decomposed so that adds to the pollution.

Question 7.
LPG gas contains butane. Its molecular formula is C₄ H₁₀. Name the possible products when it undergoes complete combustion.
Answer:
Combustion is an oxidation reaction.
2 C₄ H₁₀ + 13 O₂ → 8 CO₂ + 10 H₂O
CO₂ & H₂O are the products formed when C₄ H₁₀ undergoes complete combustion.

Question 8.
Suggest some measures to avoid the rancidity of oils, (esp food).
Answer:
Rancidity of oils can be avoided by

1. Keeping in an airtight container
2. Using antioxidants such as nitrogen
3. By doing Hydrogenation of oils.

IV. Give Scientific reasons for the following:

Question 1.
Iron displaces copper from copper sulphate but copper cannot displace, iron.
Answer:
Iron is more reactive than copper and because it lies above copper in reactivity series, it can displace Copper from copper sulfate. But copper cannot displace iron from iron sulfate as it lies below iron in reactivity series.

Question 2.
Respiration is an exothermic reaction
Answer:
Respiration is an exothermic process because it forms the highly stable C = O bonds of CO₂

Question 3.
In chemical equations, oxygen is represented as O₂ but not O and chlorine is represented as Cl₂ but not Cl
Answer:
Oxygen or chlorine are represented as ‘O₂ and ‘Cl₂” as their elements do not exist in the atomic stat, they occur only in a diatomic state.

Question 4.
Use of plastic must be avoided or minimized.
Answer:
Plastic is non-biodegradable in nature and causes pollution. Hence the usage of plastic must be avoided or minimized.

KSEEB Class 8 Science Chemical Reactions and their Types Additional Questions and Answers

Question 1.
Distinguish between physical and chemical changes
Answer:
Physical change:

• No new substance is produced
• Only physical properties of the substance are changed
• The changes are temporary.
• Heat change may or may not occur.

Chemical change:

• The new substance is produced.
• both the physical and chemical properties of the substance are
• changed.
• Change is permanent.
• Heat change must be there.

Question 2.
Classify the following into chemical and physical changes.

1. Rusting of iron
2. Ripening of fruits
3. Magnetizing a steel plate
4. melting of iron
5. combustion of LPG
6. cooling effect produced plate

Answer:

1. Rusting of iron – Chemical change
2. Ripening of fruit – Chemical change
3. Magnetizing a steel plate – Physical change
4. melting of iron – Physical change
5. combustion of L.P.G – Chemical change
6. Cooling effect produced by ice – Physical change

Question 3.
What is the main cause of the chemical reaction?
Answer:
The main cause of the chemical reaction is the desire of atoms to get a stable electronic configuration.

Question 4.
What is meant by a chemical reaction?
Answer:
The main cause of the chemical reaction is the desire of atoms to get a stable electronic configuration.

Question 5.
What are valence electrons?
Answer:
The electrons which take part in chemical reactions are called valence electrons.

Question 6.
What is meant by a chemical equation?
Answer:
A chemical equation is the symbolic representation of a reaction with the help of symbols and formulae of respective reactants and products.

Question 7.
State the Law of conservation of matter or mass,
Answer:
Law of conservation of matter or mass states that matter can neither be created nor destroyed.

Question 8.
What is the balancing of the equation?
Answer:
The practice of equalizing the number of atoms of elements on the left-hand side to the corresponding atoms on the right-hand side is called the balancing of equations.

Question 9.
Name the types of chemical reactions.
Answer:
The chemical reactions are

• Chemical combination
• Chemical decomposition
• Chemical displacement
• Chemical double displacement or exchange.

Question 10.
What is meant by chemical combination? Give an example.
Answer:
Chemical combination is a reaction in which two or more elements or compounds combine to form a new product.
Example: N₂ + 3H₂ → 2 NH₃↑

Question 11.
What do you mean by Haber’s process?
Answer:
The technology designed by Haber for synthesizing ammonia. This is done by subjecting Nitrogen and Hydrogen to high pressure at a temperature of about 500°C in the presence of a catalyst.

Question 12.
What is a chemical decomposition? Give an example.
Answer:
Chemical decomposition is a reaction in which a compound breaks up into two or more new substances.
Example: 2HgO → 2 Hg + O₂↑

Question 13.
How did Joseph Priestly prepare oxygen.?
Answer:
Joseph Priestly prepared oxygen by heating mercuric oxide in a test tube by converging sun rays using a convex lens.

Question 14.
What is meant by chemical displacement? Give an example.
Answer:
Chemical displacement is a reaction in which a more reactive element displaces less reactive elements from its compounds.
Example: CuSO₄ + Fe → Fe SO₄ + Cu

Question 15.
What is meant by chemical double decomposition? Give an example.
Answer:
Chemical double decomposition is a reaction in which there is a mutual exchange of metallic and non-metallic parts. Such reactions are also called a double chemical exchange.
Example: CaCl₂ + Na₂CO₃ → CaCO₃ ↓ + 2NaCl

Question 16.
What is meant by oxidation?
Answer:
Oxidation is a reaction in which oxygen is added to an element or compound i.e. removal of electrons from an atom Orion.

Question 17.
Mention some oxidizing agents.
Answer:
Potassium permanganate, potassium nitrate, and hydrogen peroxide are some commonly used oxidizing agents.

Question 18.
What is meant by reduction?
Answer:
Reduction is the removal of oxygen from a compound or is a process of receiving electrons.

Question 19.
Name some reducing agents.
Answer:
The common reducing agents are Carbon, Magnesium, Hydrogen sulfide, and sulfur dioxide.

II. Fill in the blanks:

1. The type of reaction in A + B → C is _______________.
2. Zinc displaces copper from Copper sulfate solution but _______________ does not displace zinc from zinc sulphate.
3. NaCl + AgNO₃ → AgCl + NaNO₃ is an example of _______________ reaction.
4. In a chemical equation, products are written on the _______________ side of the equation.
5. In the reaction, represented by the equation CuO + H₂ → Cu + H₂O _______________ is the oxidizing agent while is the reducing agent.
6. The burning of candle is a _______________ change.
7. Oxidation is loss of _______________.
8. _______________ is gain of electrons.
9. The dissolution of common salt in water js a _______________ change.
10. Joseph Priestly prepared oxygen by heating _______________ by _______________.

Answer:

1. Chemical Combination,
2. copper,
3. Exchange
4. right,
5. CuO & H₂
6. chemical
7. electrons,
8. Reduction,
9. Physical,
10. mercuric oxide, converging Sun’s rays.

III. Pick the correct option:

Question 1.
The reaction H₂ + Cl₂ → 2 HCl is a
(a) decomposition reaction
(b) combination reaction
(c) double – displacement reaction
(d) displacement reaction.
Answer:
(b) combination reaction

Question 2.
Which of the following is a decomposition reaction?
(a) NaOH + HCl → NaCl + H₂O
(b) NH₄CNO → H₂NCO + NH₂
(c) 2KClO₃ → 2KCl + 3O₂
(d) H₂ + l₂ → 2Hl
Answer:
(c) 2KClO₃ → 2KCl + 3O₂

Question 3.
Which of the following is a displacement reaction?
(a) Ca CC₃ → Ca O + CO₂
(b) Ca O + 2 H Cl → Ca Cl₂ + H₂O
(c) Fe + Cu SO₄ → Fe SO₄ + Cu
(d) Na OH + H Cl → Na Cl + H₂O
Answer:
(c) Fe + Cu SO₄ → Fe SO₄ + Cu

Question 4.
Which of the following is not a balanced equation?
(a) Mg + Cu SO₄ → Mg SO₄ + Cu
(b) Fe + Cl₂ → Fe Cl₃
(c) Ca (OH)₂ + CO₂ → Ca CO₃ + H₂O
(d) Zn + H₂SO₄ → ZnSO₄ + H₂
Answer:
(b) Fe + Cl₂ → Fe Cl₃

Question 5.
Which of the following statement is incorrect.
(a) In oxidation, electrons are lost
(b) In reduction, electrons are gained
(c) The oxidizing agent is oxidized
(d) The reducing agent is oxidized
Answer:
(c) The oxidizing agent is oxidized

IV. Balance the following equations:

1. Pb (NO₃)₂ → PbO + NO₂ + O₂
2. Al₂O₃ → Al + O₂
3. Zn + H₃ PO₄ → Zn₃ (PO₄)2 + H₂ ↑
4. Na + H₂O → Na OH + H₃↑
5. Ca (OH)₂ + HCI → Ca Cl₂ + H₂O
Answer:
1. 2 Pb (NO₃)₂ → 2 Pb O + 4 NO₂ + O₂↑
2. 2 Al₂ O₃ → 4 Al + 3 O₂
3. 3 Zn + 2 H₃ PO₄ → Zn₃ (PO₄)₂ + 3 H₂
4. 2 Na + 2 H₂O → 2 Na OH + H₂
5. Ca (OH)₂ + 2 H Cl → Ca Cl₂ + 2 H₂O