Lesson.10 TYPES OF CHEMICAL REACTIONS
Lesson 10 > TYPES OF CHEMICAL REACTIONS
I. Choose the correct answer.
1. H2(g) + Cl2(g) → 2HCl(g) is a
- Decomposition Reaction
- Combination Reaction
- Single Displacement Reaction
- Double Displacement Reaction
Ans ; (b) Combination Reaction
2. Photolysis is a decomposition reaction caused by __________.
- mechanical energy
Ans ; (c) light
3. A reaction between carbon and oxygen is represented by C(s) + O2(g) → CO2(g) + Heat. In which of the type(s), the above reaction can be classified?
|i) Combination Reaction||ii) Combustion Reaction|
|iii) Decomposition Reaction||iv) Irreversible Reaction|
- i and ii
- i and iv
- i, ii and iii
- i, ii and iv
Ans ; i, ii and iv
4. The chemical equation
Na2SO4(aq) + BaCl2(aq) → BaSO4(s))↓ + 2NaCl(aq) represents which of the following types of reaction?
- Single displacement
Ans ; Precipitation
5. Which of the following statements are correct about a chemical equilibrium?
|i) It is dynamic in nature||ii) The rate of the forward and backward reactions are equal at equilibrium|
|iii) Irreversible reactions do not attain chemical equilibrium||iv) The concentration of reactants and products may be different|
- i, ii and iii
- i, ii and iv
- ii, iii and iv
- 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.
|i) Zn||ii) Ag||iii) Cu||iv) Mg|
Choose the best pair.
- i and ii
- ii and iii
- iii and iv
- i and iv
Ans ; i and iv
7. Which of the following is not an “element + element → compound” type reaction?
- C(s) + O2(g) → CO2(g)
- 2K(s) + Br2(l) → 2KBr(s)
- 2CO(g) + O2(g) → 2CO2(g)
- 4Fe(s) + 3O2(g) → 2Fe2O3(s)
Ans ; C(s) + O2(g) → CO2(g)
8. Which of the following represents a precipitation reaction?
- A(s) + B(s) → C(s) + D(s)
- A(s) + B(aq) → C(aq) + D(l)
- A(aq) + B(aq) → C(s) + D(aq)
- 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 × 10–3 M
- 3 M
- 1 × 10–11 M
- 11 M
Ans ; 1 × 10–11 M
10. Powdered CaCO3 reacts more rapidly than flaky CaCO3 because of __________.
- large surface area
- high pressure
- high concentration
- 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 :
|1. NH4OH(aq) + CH3COOH(aq) → CH3COONH4(aq) + H2O(l)||a. Single Displacement|
|2. Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)||b. Combustion|
|3. ZnCO3(s) + Heat —- Heat—→ ZnO(s) + CO2(q)||c. Neutralisation|
|4. C2H4(g) + 4O2(g) → 2CO2(g) + 2H2O(g) + Heat||d. Thermal decomposition|
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) + AgNO3(aq) → AgCl(s)+ KNO3(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) + O2(s) → SO2(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.
- It can be reversed under suitable conditions
- Both forward and backward reactions take place simultaneously.
- It attains equilibrium.
- The reactants cannot be converted completely into products.
- It is relatively slow.
- It cannot be reversed.
- It is unidirectional. It proceeds only in forward direction.
- Equilibrium is not attained.
- The reactants can be completely converted into products.
- 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).
|2Hg(l) + O2(g)|
- 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.
|CaO(s) + CO2(g)|
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
- 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) ↓ + 2KNO3(aq)
- PbI2 form a yellow precipitate
- 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
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) +H2(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.
- 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..
- Increasing the pressure of reactant gases increases the reaction rate.
- Because, increasing pressure the reacting particles come closer and collide frequently.
- 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?
|Concentration of hydrogen ion H+
Concentration of hydrogen ion in lemon juice
|= 10-pH M
= 10-2 M= 0.01 M
Concentration of lemon juice is 0.01 M
2. Calculate the pH of 1.0 x10-4 molar solution of HNO,.
HNO3 dissociates in water as
HNO3(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+]
|Therefore [H+]||= 1.0 x 10-4|
|pH||= – log10 [H+]|
|= – log10 x log10 104|
|= – (0 – 4 x log10 10)|
|= – (4 x 1)|
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–]
|[OH–]||= 1.0 x 10-5|
|pOH||=- log10 [OH–]|
|= -log10 1.0 x 10-4|
|= -(-5)log10 1.0|
|pOH||= 5 x 1 = 5|
|pH + pOH||= 14|
|pH||= 14 – pOH|
|pH||=14-5 = 9|
The pH of 1.0 x 10-5 molar solution of KOH is 9.
4. The hydroxide ion concentration of a solution is 1 x 10-!!M. What is the pH of the
Formula used ; pOH = -log10 [OH–], pOH = 11
|[OH–]||= 1.0 x 10-11|
|pOH||=- log10 [OH-]|
|= -log10 1 x 10-11|
|= – (-11)log10 1 x 10|
|= 11 log10 10 = 11 x 1|
|pH+ pOH||= 14|
|pH||= 14 – pOH|
|pH||= 14 – 11 = 3|
pH of the hydroxide ion concentration of a solution of 1 x 10-11 M is 3
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)
CaCO3(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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