Tamil Nadu 10th Standard Science Book Solution | Lesson 10 – TYPES OF CHEMICAL REACTIONS

Lesson.10 TYPES OF CHEMICAL REACTIONS

Lesson 10 > TYPES OF CHEMICAL REACTIONS

I. Choose the correct answer.

1. H_2(g) + Cl_2(g) → 2HCl_(g) is a

1. Decomposition Reaction
2. Combination Reaction
3. Single Displacement Reaction
4. Double Displacement Reaction

Ans ; (b) Combination Reaction

2. Photolysis is a decomposition reaction caused by __________.

1. heat
2. electricity
3. light
4. mechanical energy

Ans ; (c) light

3. A reaction between carbon and oxygen is represented by C_(s) + O_2(g) → CO_2(g) + Heat. In which of the type(s), the above reaction can be classified?

1. i and ii
2. i and iv
3. i, ii and iii
4. i, ii and iv

Ans ; i, ii and iv

4. The chemical equation

Na₂SO_4(aq) + BaCl_2(aq) → BaSO_4(s))↓ + 2NaCl_(aq) represents which of the following types of reaction?

1. Neutralisation
2. Combustion
3. Precipitation
4. Single displacement

Ans ; Precipitation

5. Which of the following statements are correct about a chemical equilibrium?

1. i, ii and iii
2. i, ii and iv
3. ii, iii and iv
4. i, iii and iv

Ans ; i, ii and iv

6. A single displacement reaction is represented by X(s) + 2HCl(aq) → XCl2(aq) + H2(g). Which of the following(s) could be X.

Choose the best pair.

1. i and ii
2. ii and iii
3. iii and iv
4. i and iv

Ans ; i and iv

7. Which of the following is not an “element + element → compound” type reaction?

1. C_(s) + O_2(g) → CO_2(g)
2. 2K_(s) + Br2_(l) → 2KBr_(s)
3. 2CO_(g) + O_2(g) → 2CO_2(g)
4. 4Fe_(s) + 3O_2(g) → 2Fe₂O_3(s)

Ans ; C_(s) + O_2(g) → CO_2(g)

8. Which of the following represents a precipitation reaction?

1. A_(s) + B_(s) → C_(s) + D_(s)
2. A_(s) + B_(aq) → C_(aq) + D_(l)
3. A_(aq) + B_(aq) → C_(s) + D_(aq)
4. A_(aq) + B_(s) → C_(aq) + D_(l)

Ans ; A_(aq) + B_(aq) → C_(s) + D_(aq)

9. The pH of a solution is 3. Its [OH–] concentration is

1. 1 × 10^–3 M
2. 3 M
3. 1 × 10^–11 M
4. 11 M

Ans ; 1 × 10^–11 M

10. Powdered CaCO₃ reacts more rapidly than flaky CaCO₃ because of __________.

1. large surface area
2. high pressure
3. high concentration
4. high temperature

Ans : (a) large surface area

II. Fill in the blanks

1. A reaction between an acid and a base is called __________.

Ans ; neutralisation reaction

2. When lithium metal is placed in hydrochloric acid, __________ gas is evolved.

Ans ; hydrogen

3. The equilibrium attained during the melting of ice is known as __________.

Ans ; Physical equilibrium

4. The pH of a fruit juice is 5.6. If you add slaked lime to this juice, its pH __________ (increse/decrese)

Ans ; increases

5. The value of ionic product of water at 250 C is __________.

Ans ; 1.00 × 10^–14 mol² dm^–6

6. The normal pH of human blood is __________.

Ans ; 7.35 to 7.45

7. Electrolysis is type of __________ reaction.

Ans ; decomposition

8. The number of products formed in a synthesis reaction is __________.

Ans ; one

9. Chemical volcano is an example for __________ type of reaction.

Ans ; decomposition

10. The ion formed by dissolution of H+ in water is called __________.

Ans ; Hydronium ion H3O+

III. Match the following

Identify the types of reaction :

Ans : 1- c, 2 -a, 3 – d, 4 – b

IV. True or false (If false give the correct statement)

1. Silver metal can displace hydrogen gas from nitric acid. ( False )

• Silver metal cannot displace hydrogen gas from Nitric acid.

2. The pH of rain water containing dissolved gases like SO₃, CO₂, NO₂ will be less than 7.  ( True )

3. At the equilibrium of a reversible reaction, the concentration of the reactants and the products will be equal. ( True )

4. Periodical removal of one of the products of a reversible reaction increases the yield. ( True )

5. On dipping a pH paper in a solution, it turns into yellow. Then the solution is basic. ( True )

VI. Short answer questions:

1. When an aqueous solution of potassium chloride is added to an aqueous solution of silver nitrate, a white precipitate is formed. Give the chemical equation of this reaction.

KCl_(aq) + AgNO_3(aq) → AgCl_(s)+ KNO_3(aq)

White precipitate of AgCl is formed in aqueous solution of potassium nitrate.

2. Why does the reaction rate of a reaction increase on raising the temperature?

• The temperature of a reaction increases, the adding heat provides energy to break more bonds of the reactant molecules.
• So more reactants ions increases, produce more products.
• Thus speed of the reaction increases.

3. Define combination reaction. Give one example for an exothermic combination reaction.

• A combination reaction is a reaction in which two or more reactants combine to form a compound.
• It is also called as synthesis reaction (or) composition reaction (a single product).
• S_(s) + O_2(s) → SO_2(s)
• Sulphur reacts with oxygen and produce sulphur di-oxide.
• Most of combination reactions are exothermic in nature, because they involve the formation of new.

4. Differentiate reversible and irreversible reactions.

Reversible:-

1. It can be reversed under suitable conditions
2. Both forward and backward reactions take place simultaneously.
3. It attains equilibrium.
4. The reactants cannot be converted completely into products.
5. It is relatively slow.

Irreversible:-

1. It cannot be reversed.
2. It is unidirectional. It proceeds only in forward direction.
3. Equilibrium is not attained.
4. The reactants can be completely converted into products.
5. It is fast.

VII. Answer in detail

1. What is thermolysis reaction?

• In a decomposition reaction, a single compound splits into two or more simpler substances by the help of heat. It is called “‘Thermolysis’.
• For example, It is a class of compound to element/element decomposition. ie. a compound (HgO) is decomposed into two elements (Hg and Oxygen).
  heat

• In thermal decomposition reaction, heat is supplied to break the bonds.
• Such reactions, in which heat is absorbed, are called ‘Endothermic reactions’
• When calcium carbonate is heated, it breaks down into calcium oxide and carbon dioxide.
• It is a type of compound to compound/compound decomposition.

2. Explain the types of double displacement reactions with examples.

• When two compounds react, if their ions are interchanged, then the reaction is called double displacement reaction.
• There are major classes of double displacement reactions. They are:
• Precipitation Reactions
• Neutralization Reactions

Precipitation Reactions:

• When aqueous solutions of two compounds are mixed, if they react to form an insoluble compound and a soluble compound, then it is called precipitation reaction.

Aqueous Solution + Aqueous Solution ———> Insoluble compound + Soluble compound

• When the clear aqueous solutions of potassium iodide and lead (TI) nitrate are mixed, a double displacement reaction takes place between them.

Pb(NO₃)_2(aq) + 2RI(ag) ———> PhI_(aq)  ↓ + 2KNO_3(aq)

• PbI₂ form a yellow precipitate

Neutralization Reactions:

• It is a type of displacement reaction in which the acid reacts with the base to form a salt and water.
• It is called ‘neutralization reaction’ as both acid and base neutralize each other.

Acid + Base ———> Salt + Water

• Reaction of sodium hydroxide with hydrochloric acid is a typical neutralization reaction.
• Here, sodium displaces hydrogen from hydrochloric acid forming sodium chloride, a neutral soluble salt.

NaOH_(aq) + HCl_(aq) > NaCl_(aq) + H₂O_(i)

3. Explain the factors influencing the rate of a reaction

Important factors that affect trate of a reaction are

• Nature of the reactants
• Concentration of the reactants
• Temperature
• Catalyst
• Pressure

Surface area of the reactants

Nature of the reactants:

• The reaction of sodium with hydrochloric acid is faster than that with acetic acid.
• Because Hydrochloric acid is a stronger acid than acetic acid and thus more reactive.
• 2Na_(S) + 2HCl_(aq) ———> 2NaCl_(aq) +H_2(q) ———> (fast)
• 2Na_(S) + 2CH₃COOH_(aq) ———> 2CH₃COONA_(aq) + H_(2G) ———> (slow)

Concentration of the reactants:

• The amount of the substance present in a certain volume of the solution is called concentration.
• More the concentration, more particles per yolume exist in it and faster the reaction.
• Granulated zinc reacts faster with 2M hydrochloric acid than 1M hydrochloric acid.

Temperature:

• Most of the reactions go faster at higher temperature.
• Because adding heat to the reactants provides energy to break more bonds and thus speed up the reaction.
• E.g: Calcium carbonate reacts slowly with hydrochloric acid at room temperature and faster when temperature increases..

Pressure:

• Increasing the pressure of reactant gases increases the reaction rate.
• Because, increasing pressure the reacting particles come closer and collide frequently.

Catalyst:

• A catalyst is a substance which increases the reaction rate without being consumed in the reaction.
• E.g: On heating potassium chlorate, it decomposes into potassium chloride and oxygen gas, but at a slower rate.
• If manganese dioxide is added, it increases the reaction rate.

Surface area of the reactants:

• When solid reactants are involved in a reaction, their powdered form reacts more readily.
• Because, powdering of the reactants increases the surface area and more energy is available on collision of the reactant particles.
• Thus, the reaction rate is increased.
• E.g: Powdered calcium carbonate reacts more readily with hydrochloric acid than marble chips.

4. How does pH play an important role in everyday life?

• Our body works within the pH range of 7.0 to 7.8.
• Different body fluids have different pH values.
• For example, pH of blood is ranging from 7.35 to 7.45.
• Any increase or decrease in this value leads to diseases.
• The ideal pH for blood is 7.4.

pH in our digestive system:

•  HCl present in our stomach helps in digestion.
  During indigestion our stomach produces more acid and this causes pain and irritation.
• pH of the stomach fluid is approximately 2.0.

pH changes as the cause of tooth decay:

• pH of the saliva normally ranges between 6.5 to 7.5.
• White enamel coating (calcium phosphate) is a hard substance in our body.
• When the pH value falls below 5.5, it weathers.
• The basic toothpaste neutralises the excess acid and prevents tooth decay.
  pH of soil:
• Citrus fruits require slightly alkaline soil, rice requires acidic soil and sugarcane requires neutral soil.

pH of rain water:

• The pH of rain water is approximately 7.
• 0If the atmospheric air is polluted with oxides of non-metals, they get dissolved in the rain water and make its pH less than 7.
• As its pH value is less than 7, then it is called acid rain.
• When this rain water reaches river water, the survival of aquatic life becomes difficult.

5. What is a chemical equilibrium? What are its characteristics? * 2K OK

• Chemical equilibrium is a state of a reversable chemical reaction in which no change in theamount of the reactants and products takes place.
• At equilibrium

Rate of forward reaction = Rate of backward reaction

Characteristics of equilibrium:

• In a chemical equilibrium, the rate of forward and backward reactions are equal.
• The observable properties such as pressure, concentration, colour, density, viscosity, etc., of the system remain unchanged with time.
• The chemical equilibrium is a dynamic equilibrium, because both the forward and backward reactions continue to occur even though it appears static externally.
• In physical equilibrium, the volume of all the phases remain constant.

VIII. Solve the following problems

1. Lemon juice has a pH 2, what is the concentration of H* ions?

2. Calculate the pH of 1.0 x10^-4 molar solution of HNO,.

HNO₃ dissociates in water as
HNO_3(aq) → H⁺ +NO₃^–
Each Nitric acid gives one H* ions in water. So 1.0 x 10^-4 molar solution of HNO₃ gives 1.0 x 10^-4 moles of ions in water.

Formula used ; pH = – log₁₀ [H⁺]

3. What is the pH of 1.0 x 10^-5 molar solution of KOH?

KOH is a strong base and dissolve in water and gives

KOH = K⁺+OH^–

Each KOH molecules gives one OH^– ion. So 1.0 x 10^-5molar solution of KOH gives 1.0 x 10^-5 OH^– ions.

Formula used ; pOH = -log₁₀ [OH^–]

4. The hydroxide ion concentration of a solution is 1 x 10-!!M. What is the pH of the
solution?

Formula used ; pOH = -log₁₀ [OH^–], pOH = 11

Types of Chemical Reactions

IX. Higher Order Thinking Skill (HOTS)

1. A solid compound ‘A’ decomposes on heating into ‘B’ and a gas ‘C’ On passing the gas ‘C’ through water, it becomes acidic. Identify A, B and C. ?

• On passing ‘C’ through water it becomes acidic.
• Therefore the gas ‘C’ must be a non-metal oxide (CO,).
• Soa solid compound must bea calcium carbonate.
• It decomposes into calcium oxide and carbon dioxide. (C)

CaCO_3(g) → CaO_(s) + CO)_2(g)

A             B             C

• A ——> CaCO₃
• B  ——> CaO
• C ——> CO₂

2. Cana nickel spatula be used to stir copper sulphate solution? Justify your answer.

• No, because Nickel is more reactive than Copper.
• So Nickel easily reacts and displaces copper from copper sulphate solution.
• Ni₍₂₎ + Cu_(aq) > Ni_(aq) + Cu_(s)

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