10th Chemical Reactions & Equations Question Bank (Science)

Chemical Reactions And Equations Question Bank

Question 1:

Which of the following reactions is an endothermic reaction?

• (a) Burning of coal.
• (b) Decomposition of vegetable matter into compost.
• (c) Process of respiration.
• (d) Decomposition of calcium carbonate to form quick lime and carbon dioxide.

Answer: (d) Decomposition of calcium carbonate to form quick lime and carbon dioxide.

Explanation: Decomposition of calcium carbonate to form quick lime and carbon dioxide is an endothermic reaction since this process absorbs heat from the atmosphere.

Question 2:

Zn + HCl → ZnCl₂ + ________.

• (a) H₂
• (b) Cl₂
• (c) Zn
• (d) None of these

Answer: (a) H₂

Explanation: Zn + HCl → ZnCl₂ + H₂
Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions.

Question 3:

Which among the following statement(s) is (are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to:

• (i) The formation of silver by decomposition of silver chloride.
• (ii) Sublimation of silver chloride.
• (iii) Decomposition of chlorine gas from silver chloride.
• (iv) Oxidation of silver chloride.

• (a) (i) only
• (b) (i) and (iii)
• (c) (ii) and (iii)
• (d) (iv) only

Answer: (a) (i) only

Explanation: Exposure of silver chloride to sunlight for a long duration turns silver chloride grey due to the photolysis reaction in which the decomposition of the silver chloride takes place in the presence of sunlight leading to the formation of silver.

Question 4:

The reaction which decomposes after the supply of heat is called ________.

• (a) Thermal decomposition
• (b) Combination reaction
• (c) Redox reaction
• (d) Displacement reaction

Answer: (a) Thermal decomposition

Question 5:

In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:

1. exchange of atoms takes place.
2. exchange of ions takes place.
3. a precipitate is produced.
4. an insoluble salt is produced.

• (a) (ii) and (iv)
• (b) (i) and (iii)
• (c) only (ii)
• (d) (ii), (iii) and (iv)

Answer: (d) (ii), (iii) and (iv)

Explanation: In a double displacement reaction, sodium sulphate reacts with barium chloride to form an insoluble white precipitate of barium sulphate and sodium chloride. Here, exchange of ions takes place.

Question 6:

Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is _______.

• (a) 1:1
• (b) 2:1
• (c) 4:1
• (d) 1:2

Answer: (b) 2:1

Explanation: The mole ratio of hydrogen and oxygen gases liberated during the electrolysis of water is 2:1. Since two atoms of hydrogen and one atom of oxygen are present in the water molecule respectively.
2H₂O → 2H₂ + O₂

Question 7:

Which of the following is an example of simple displacement?

• (a) the electrolysis of water
• (b) the burning of methane
• (c) the reaction of a metal with an acid
• (d) the reaction of two salt solutions to form a precipitate

Answer: (c) the reaction of a metal with an acid

Explanation: The displacement reaction is the one where an atom or a set of atoms is displaced by another atom in a molecule. For example, when iron is added to a copper sulphate solution, it displaces copper metal: A + B–C → A–C + B.

Question 8:

Which law should be kept in mind while we balance chemical equations?

• (a) Conservation of momentum
• (b) Conservation of mass
• (c) Conservation of energy
• (d) Conservation of frequency

Answer: (b) Conservation of mass

Explanation: The law of conservation of mass states that “mass can neither be created nor destroyed.” So, both sides of the chemical reactions must be balanced to follow this law, ensuring the number of reactant and product molecules remains the same.

Question 9:

In which of the following, the identity of initial substance remains unchanged?

• (a) Curdling of milk
• (b) Formation of crystals by process of crystallisation
• (c) Fermentation of grapes
• (d) Digestion of food

Answer: (b) Formation of crystals by process of crystallisation

Explanation: In crystallisation, the original identity of the substance remains as such, even when converted into powder form and back again to crystals upon heating and cooling.

Question 10:

Which one of the following processes involves a chemical reaction?

• (a) Liquification of air
• (b) Heating copper wire in presence of air at high temperature
• (c) Keeping petrol in a china dish in the open
• (d) Storing of oxygen gas under pressure in a gas cylinder

Answer: (b) Heating copper wire in presence of air at high temperature

Explanation: A chemical reaction occurs when heating copper wire in air at high temperature. Other processes like liquification or storing gases are physical changes as no new substance is formed.

Question 11:

Which of the following gases can be used for storage of fresh sample of an oil for a long time?

• (a) Carbon dioxide
• (b) Hydrogen
• (c) Nitrogen
• (d) Helium

Answer: (d) Helium

Explanation: Helium can be used to store fresh samples of oil for a long time since it is an inert gas and does not react with the sample, preserving its quality.

Question 12:

Shashank was asked to carry out a displacement reaction which would show the following:

• (i) Formation of colourless solution
• (ii) Black deposits

The reactants he should use are:

• (a) Fe(s) and Al₂(SO₄)₃(aq)
• (b) Al(s) and FeSO₄(aq)
• (c) Zn(s) and CuSO₄(aq)
• (d) Fe(s) and ZnSO₄(aq)

Answer: (b) Al(s) and FeSO₄(aq)

Explanation: Aluminium displaces iron from ferrous sulphate, forming aluminium sulphate (colourless solution) and depositing greyish black iron.

Question 13:

The oxidation reaction which produces heat and light is called:

• (a) Endothermic
• (b) Photochemical
• (c) Exothermic
• (d) Combustion

Answer: (d) Combustion

Explanation: A combustion reaction is a type of chemical reaction where a substance combines with oxygen to release heat and light.

Question 14:

Heating of ferrous sulphate is a type of:

• (a) Decomposition reaction
• (b) Combination reaction
• (c) Displacement reaction
• (d) All of the above

Answer: (a) Decomposition reaction

Explanation: Heating of ferrous sulphate leads to decomposition into ferric oxide, sulphur dioxide, and sulphur trioxide. It's an endothermic decomposition reaction.

Question 15:

To balance Al(OH)₃ + HNO₃ → Al(NO₃)₃ + H₂O, number of HNO₃ molecules required will be:

• (a) 2
• (b) 4
• (c) 3
• (d) 8

Answer: (c) 3

Explanation: Three molecules of HNO₃ are required to satisfy the law of conservation of mass.
Al(OH)₃ + 3HNO₃ → Al(NO₃)₃ + 3H₂O

Question 16:

Which metal is displaced when lead is put in the solution of copper chloride?

• (a) Lead
• (b) Copper
• (c) Chlorine
• (d) All of these

Answer: (b) Copper

Explanation: Lead displaces copper from copper chloride as it is more reactive, resulting in the deposition of copper.

Question 17:

What is the name of the process where fatty foods become rancid?

• (a) Corrosion
• (b) Oxidation
• (c) Reduction
• (d) Hydrogenation

Answer: (b) Oxidation

Explanation: Rancidity is caused by the oxidation of fats and oils in foods, leading to a change in taste and smell due to aerial oxidation.

Question 18:

Rancidity can be prevented by:

• (a) adding antioxidants
• (b) storing food away from light
• (c) keeping food in refrigerator
• (d) all of the above

Answer: (d) all of the above

Explanation: Rancidity can be prevented by all mentioned methods: using antioxidants, avoiding exposure to light, and storing in cool environments.

Chemical Reactions and Equations - Question Bank

Question 19:

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.

1. N₂(g) + 3H₂(g) → 2NH₃(g)
   Type: Combination Reaction
2. NaOH(aq) + CH₃COOH(aq) → CH₃COONa(aq) + H₂O(l)
   Type: Double Displacement or Neutralisation Reaction
3. C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O
   Type: Esterification Reaction
4. C₂H₄ + 3O₂ → 2CO₂ + 2H₂O
   Type: Combustion Reaction
5. KCl(aq) + AgNO₃(aq) → AgCl(s) ↓ + KNO₃(aq)
   Type: Double Displacement and Precipitation Reaction
6. 2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)
   Type: Thermal Decomposition Reaction

Question 20:

"Dil. HCl is added to Zn granules." How will you prove that chemical change has taken place here? Support your response with two arguments.

Answer:

1. The colour of zinc metal changes from silvery grey to black.
2. Colourless and odourless hydrogen gas is evolved, which is visible as small bubbles.

Question 21:

Identify the reducing agent in the following reactions:

1. 4NH₃ + 5O₂ → 4NO + 6H₂O
   Ans: Ammonia (NH₃)
2. H₂O + F₂ → HF + HOF
   Ans: Water (H₂O)
3. Fe₂O₃ + 3CO → 2Fe + 3CO₂
   Ans: Carbon monoxide (CO)
4. 2H₂ + O₂ → 2H₂O
   Ans: Hydrogen (H₂)

Question 22:

Write the balanced chemical equations for the following reactions:

1. Sodium carbonate reacts with hydrochloric acid in equal molar concentrations.
   Na₂CO₃(aq) + HCl(aq) → NaHCO₃(aq) + NaCl(aq)
2. Sodium hydrogencarbonate reacts with hydrochloric acid.
   NaHCO₃(aq) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g)
3. Copper sulphate reacts with potassium iodide.
   2CuSO₄(aq) + 4KI(aq) → Cu₂I₂(s) + 2K₂SO₄(aq) + I₂(s)

Question 23:

Balance the following chemical equations and identify the type of chemical reaction:

1. Mg(s) + Cl₂(g) → MgCl₂(s)
   Type: Combination Reaction
2. HgO(s) Heat → Hg(l) + O₂(g)
   Type: Decomposition Reaction
3. Na(s) + S(s) Fuse → Na₂S
   Type: Combination Reaction
4. TiCl₄(l) + Mg(s) → Ti(s) + MgCl₂(s)
   Type: Displacement Reaction

Question 24:

Write the balanced equation for the following chemical reactions:

1. H₂(g) + Cl₂(g) → 2HCl(g)
2. 3BaCl₂(aq) + Al₂(SO₄)₃(aq) → 3BaSO₄(s) + 2AlCl₃(aq)
3. 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

Question 25:

Complete the following reactions:

1. NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
2. AgNO₃(aq) + NaCl(aq) → AgCl(s) ↓ + NaNO₃(aq)
3. Na₂O(s) + H₂O(l) → 2NaOH(aq)
4. Ca(HCO₃)₂(aq) + Ca(OH)₂(aq) → 2CaCO₃(s) ↓ + 2H₂O(l)
5. Cu(s) + 2H₂SO₄(dil) → CuSO₄(aq) + SO₂(g) + 2H₂O(l)
6. 2Mg(s) + O₂(g) → 2MgO(s)

Question 26:

Classify the following reactions:

1. Reaction of magnesium and oxygen to form magnesium oxide.
   Ans: Combination reaction
2. Heating of calcium carbonate.
   Ans: Decomposition reaction
3. Reaction of potassium hydroxide and nitric acid to form potassium nitrate and water.
   Ans: Neutralisation reaction
4. Reaction of zinc oxide and carbon to form zinc and carbon monoxide.
   Ans: Redox reaction

Question 27:

What happens when ZnCO₃ is heated in the absence of air? Give the relevant equation. [Board Question]

Answer:

When ZnCO₃ is heated in the absence of air, zinc oxide (ZnO) and carbon dioxide (CO₂) are formed.

ZnCO₃ → ZnO + CO₂

Question 28:

Complete and balance the following chemical equations: [Board Question]

1. CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
2. 2Al(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂(g)
3. MnO₂(s) + 4HCl(aq) → MnCl₂(aq) + Cl₂(g) + 2H₂O(l)

Question 29:

A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of chemical reaction?

Answer:

KCl(aq) + AgNO₃(aq) → AgCl(s) ↓ + KNO₃(aq)

(Silver chloride – White ppt.)
It is a double displacement and precipitation reaction.

Question 30:

What happens when ZnCO₃ is heated in the absence of air? Give the relevant equation. [Board Question]

Answer:

ZnCO₃ → ZnO + CO₂

Question 31:

What happens when quick lime is added to water? [Board Question]

Answer:

When quick lime is added to water, it produces calcium hydroxide (slaked lime) with evolution of large amount of heat.

CaO(s) + H₂O → Ca(OH)₂ + Heat

Question 32:

A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.

Answer:

Substance X is Calcium oxide.

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

Question 33:

AgNO₃(aq) + NaCl(aq) → AgCl(s) ↓ + NaNO₃(aq)
FeS + H₂SO₄ → FeSO₄ + H₂S ↑
Consider the above mentioned two chemical equations with two different kinds of arrows (↓ and ↑) along with product. What do these two different arrows indicate? [Board Question]

Answer:

↑ shows evolution of gas whereas ↓ shows formation of precipitate.

Question 34:

What change in colour is observed when white silver chloride is left exposed to sunlight? State the type of chemical reaction in this change. [Board Question]

Answer:

When white silver chloride is left exposed to sunlight, it becomes grey. It is a photochemical decomposition reaction.

Question 35:

When limestone is heated it decomposes into quick lime and carbon dioxide gas. Write the chemical equation for this reaction.

Answer:

CaCO₃(s) Heat → CaO(s) + CO₂(g)

(Limestone → Quick lime + Carbon dioxide)

Question 36:

What happens when magnesium ribbon burns in air?

Answer:

2Mg(s) + O₂(g) → 2MgO(s)

Question 37:

State the following:

1. The type of chemical reaction used for extraction of metals from their naturally occurring chlorides or oxides?
   Ans: Displacement reaction
2. The type of chemical reaction used for obtaining a metal from its oxide?
   Ans: Reduction
3. Identify the type of reaction: Zn + CuSO₄ → ZnSO₄ + Cu
   Ans: Displacement reaction
4. The type of reaction used in photography?
   Ans: Decomposition reaction
5. An example of endothermic reaction?
   Ans: Decomposition of calcium carbonate
6. A reaction that takes place during digestion of food in our body?
   Ans: Decomposition reaction
7. Quick lime and slaked lime.
   Ans: CaO (quick lime), Ca(OH)₂ (slaked lime)
8. A gas evolved when Zn reacts with hydrochloric acid?
   Ans: Hydrogen (H₂)
9. A substance used in white washing?
   Ans: Calcium oxide
10. An example of double displacement reaction.
    Ans: Na₂SO₄ + BaCl₂ → BaSO₄ ↓ + 2NaCl
11. Is burning a candle a physical change or a chemical change? [Board Question]
    Ans: Chemical change
12. Which one is a chemical change: rusting of iron or melting of iron?
    Ans: Rusting of iron

Question 38:

A white salt on heating decomposes to give brown fumes and a residue is left behind.

1. Name the salt.
2. Write the equation for the decomposition reaction. [Board Question]

Answer:

1. The white salt is lead nitrate.
2. 2Pb(NO₃)₂(s) Heat → 2PbO(s) + 4NO₂(g) + O₂(g)
   (Brown fumes of nitrogen dioxide gas)

Question 39:

When the powder of a common metal is heated in an open china dish, its colour turns black. However, when hydrogen is passed over the hot black substance so formed, it regains its original colour. Based on the above information, answer the following questions. [Board Question]

1. What type of chemical reaction takes place in each of the two given steps?
2. Name the metal initially taken in the powder form. Write balanced chemical equations for both reactions.

Answer:

1. Oxidation occurs in the first step, redox reaction in the second.
2. Metal: Copper
   2Cu(s) + O₂(g) → 2CuO(s)
   CuO + H₂(g) Heat → Cu(s) + H₂O(g)

Question 40:

Answer the following questions: [Board Question]

1. Why is respiration considered as an exothermic reaction?
2. Define the terms oxidation and reduction.
3. Identify the substance that is oxidised and reduced in the following reaction:
   CuO + Zn → ZnO + Cu

Answer:

1. Respiration is exothermic because energy is released by oxidation of food.
2. Oxidation: addition of O₂ or removal of H₂.
   Reduction: addition of H₂ or removal of O₂.
3. Zn is oxidised, CuO is reduced.

Question 41:

The following diagram displays a chemical reaction. Observe carefully and answer the following questions: [Board Question]

1. Identify the type of chemical reaction that will take place and define it. How will the colour of the salt change?
2. Write the chemical equation of the reaction that takes place.
3. Mention one commercial use of this salt.

Answer:

1. Photochemical decomposition reaction. A compound breaks down in presence of light. Colour changes from white to grey.
2. 2AgCl(s) Sunlight → 2Ag(s) + Cl₂(g)
3. Used in photography.

Question 42:

State the type of chemical reactions and chemical equations that take place in the following:

Answer:

(i) Magnesium wire is burnt in air.
2Mg(s) + O₂(g) → 2MgO(s)
Type: Combination reaction

Question 43:

Answer the following questions:

1. Write the essential condition for the following reaction to take place:
   2AgBr → 2Ag + Br₂
   Answer: The reaction takes place in the presence of light. This reaction is used in photography.
2. Complete the following chemical equation of a chemical reaction:
   2FeSO₄ Heat → Fe₂O₃ + _______ + _______
   Answer: SO₂(g) + SO₃(g)
3. What happens when water is added to quick lime? Write chemical equation.
   Answer:
   Slaked lime is formed with hissing sound and lot of heat is evolved.
   CaO + H₂O → Ca(OH)₂
   (Calcium hydroxide – slaked lime)

Question 44:

Identify the type of each of the following reactions. Also write the balanced chemical equation involved. [Board Question]

1. The reaction mixture becomes warm.
   Answer: It is an exothermic reaction. Energy is released, warming the mixture.
   CaO + H₂O → Ca(OH)₂ + Heat
2. An insoluble substance is formed.
   Answer: It is a precipitation reaction. A curdy white precipitate of silver chloride is formed.
   AgNO₃(aq) + NaCl(aq) → AgCl(s) ↓ + NaNO₃(aq)

Question 45:

Write the chemical equation involved in the following chemical reactions: [Board Question]

1. White washing
   Answer:
   CaO + H₂O → Ca(OH)₂ + Heat
   Calcium oxide reacts with water to form slaked lime with energy release.
2. Black and White photography
   Answer:
   2AgBr(s) Sunlight → 2Ag(s) + Br₂(g)
   Silver bromide decomposes in sunlight to give silver and bromine. (Light yellow → Grey)

Question 46:

2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for some time. What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction. [Board Question]

Answer:

Initially the colour of silver chloride is white, but on exposure to sunlight, it decomposes to silver and chlorine, turning grey.
Equation: 2AgCl(s) Sunlight → 2Ag(s) + Cl₂(g)
Type: Photo-chemical decomposition

Question 47:

Answer the following questions: [Board Question]

1. 1. By adding antioxidants to food containing fat and oil, e.g., butylated hydroxy anisole is added to butter as an antioxidant.
   2. By packaging fat and oil containing foods in nitrogen gas.
2. Importance of decomposition reaction:
   1. In metallurgy for refining of metals.
   2. Extracting high reactive metals from their molten chlorides (Molten sodium chloride).
   3. Electrolysis of water gives large scale production of hydrogen gas and oxygen gas.

Question 48:

Identify the type of chemical reaction in the following statements and define each of them. [Board Question]

1. Decomposition reaction – food is broken into simpler substances like glucose, amino acids, etc.
2. Oxidation reaction – iron reacts with oxygen and moisture to form iron oxide (rust).
3. Displacement reaction – aluminium (more reactive) displaces manganese from manganese dioxide.
4. Displacement reaction – iron displaces copper from copper sulphate solution.
5. Neutralisation (double displacement) – acid and base react to form salt and water.

Question 49:

Write the differences between a physical and a chemical change.

Differentiate Between

Physical Change	Chemical Change
It is a temporary change and easily reversible.	It is a permanent change and sometimes reversible.
It does not form a new product.	It forms a new product.
This change involves the change in the physical states of the substance.	This change involves the change in the chemical composition of the substance.

Question 50:

Give reason and name the type of chemical reaction taking place in each case:

1. Dissolution of ammonium chloride in water is an endothermic reaction where heat is absorbed from surroundings making it cooler.
   NH₄Cl(s) + H₂O(l) → NH₄OH(aq) + HCl(aq)
2. Silver chloride undergoes decomposition reaction in sunlight to form silver and chlorine gas.
   2AgCl(s) Sunlight → 2Ag(s) + Cl₂(g)
   (White → Grey)
3. Iron displaces copper from its solution, so the blue colour of copper sulphate fades. This is a displacement reaction.
   Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
   (Blue → Less blue / colourless)