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Chapter 6 CHEMICAL REACTIONS

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 ICSE CHEMISTRY CLASS 8

Chapter: Chemical Reactions

Introduction to Chemical Reactions: Chemical reactions are fundamental processes in which substances interact, leading to the formation of new substances with different properties. These reactions play a crucial role in daily life, industry, and natural processes.

Key Concepts:

  1. Reactants and Products:

    • Reactants are the initial substances participating in a chemical reaction.

    • Products are the new substances formed as a result of the reaction.

  2. Chemical Equations:

    • Chemical reactions are represented using chemical equations.

    • Reactants are written on the left side, and products are written on the right side.

    • The arrow (→) indicates the direction of the reaction.

  3. Types of Chemical Reactions:

    • Combination Reaction: Two or more substances combine to form a single product.

    • Decomposition Reaction: A single compound breaks down into two or more simpler substances.

    • Displacement Reaction: Atoms or ions of one substance replace those of another in a compound.

    • Double Displacement Reaction: Exchange of ions between two compounds to form new compounds.

    • Redox Reaction (Oxidation-Reduction): Transfer of electrons between reactants.

  4. Balancing Chemical Equations:

    • The law of conservation of mass states that the total mass of reactants equals the total mass of products.

    • Chemical equations must be balanced by adjusting coefficients to ensure atoms on both sides are equal.

  5. Endothermic and Exothermic Reactions:

    • Endothermic reactions absorb heat energy from the surroundings.

    • Exothermic reactions release heat energy into the surroundings.

  6. Catalysts and Inhibitors:

    • Catalysts increase the rate of a reaction without being consumed.

    • Inhibitors decrease the rate of a reaction.

Examples of Chemical Reactions:

  1. Combination Reaction:

    • Example: Hydrogen gas and oxygen gas combine to form water.

    • Chemical Equation: 2H₂ + O₂ → 2H₂O

  2. Decomposition Reaction:

    • Example: Calcium carbonate decomposes into calcium oxide and carbon dioxide when heated.

    • Chemical Equation: CaCO₃ → CaO + CO₂

  3. Displacement Reaction:

    • Example: Zinc displaces copper from copper sulfate solution.

    • Chemical Equation: Zn + CuSO₄ → ZnSO₄ + Cu

  4. Double Displacement Reaction:

    • Example: Sodium chloride reacts with silver nitrate to form sodium nitrate and silver chloride.

    • Chemical Equation: NaCl + AgNO₃ → NaNO₃ + AgCl

  5. Redox Reaction (Oxidation-Reduction):

    • Example: Hydrogen reacts with oxygen to form water.

    • Chemical Equation: 2H₂ + O₂ → 2H₂O

Applications of Chemical Reactions:

  1. Metabolism: Chemical reactions in living organisms, such as digestion and respiration.

  2. Corrosion: Metal objects rust due to chemical reactions with oxygen and moisture.

  3. Combustion: Burning of fuels involves exothermic redox reactions.

  4. Cooking: Heat-induced chemical reactions in food preparation.

  5. Chemical Synthesis: Manufacturing of various products, such as fertilizers and pharmaceuticals.

Conclusion: Understanding chemical reactions is essential for comprehending the transformations of matter in our surroundings. Different types of reactions play diverse roles in nature, industry, and our daily lives, shaping the world around us through the creation and alteration of substances.


Question Bank :


Here are 15 questions and answers based on the ICSE Class 8 syllabus for the chapter "Chemical Reactions":


Questions:


Q1: What are chemical reactions?

A1: Chemical reactions are processes in which substances interact to form new substances with different properties.


Q2: How are reactants and products represented in a chemical equation?

A2: Reactants are written on the left side, and products are written on the right side of a chemical equation.


Q3: What is a balanced chemical equation?

A3: A balanced chemical equation has an equal number of atoms of each element on both sides.


Q4: State the law of conservation of mass.

A4: The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction; it is conserved.


Q5: Define endothermic and exothermic reactions.

A5: Endothermic reactions absorb heat energy, while exothermic reactions release heat energy.


Q6: Give an example of a decomposition reaction.

A6: Heating calcium carbonate (CaCO₃) to form calcium oxide (CaO) and carbon dioxide (CO₂).


Q7: What happens in a displacement reaction?

A7: Atoms or ions of one substance replace those of another in a compound.


Q8: Explain double displacement reaction with an example.

A8: In a double displacement reaction, ions exchange between two compounds to form new compounds. Example: Sodium chloride (NaCl) and silver nitrate (AgNO₃) form sodium nitrate (NaNO₃) and silver chloride (AgCl).


Q9: What is a redox reaction?

A9: A redox (oxidation-reduction) reaction involves the transfer of electrons between reactants.


Q10: What is the role of a catalyst in a chemical reaction?

A10: A catalyst increases the rate of a reaction without being consumed.


Q11: Provide an example of a combustion reaction.

A11: The burning of methane (CH₄) in the presence of oxygen to produce carbon dioxide (CO₂) and water (H₂O).


Q12: How do inhibitors affect a chemical reaction?

A12: Inhibitors decrease the rate of a reaction by interfering with the reaction mechanism.


Q13: What is the importance of balancing chemical equations?

A13: Balancing ensures the law of conservation of mass is followed and that atoms are conserved in a reaction.


Q14: Explain the role of chemical reactions in digestion.

A14: Chemical reactions in digestion break down complex food molecules into simpler substances for absorption.


Q15: How does corrosion demonstrate chemical reactions?

A15: Corrosion, such as rusting of metals, involves chemical reactions with substances like oxygen and moisture.


Here are 15 multiple-choice questions (MCQs) along with their answers, based on the ICSE Class 8 syllabus for the chapter "Chemical Reactions":



Questions:


Q1: Which of the following is a chemical reaction?

a) Boiling water

b) Melting ice

c) Dissolving sugar in water

d) Burning paper

Answer: d) Burning paper


Q2: In a chemical equation, the reactants are written on the:

a) Left side

b) Right side

c) Middle

d) Top

Answer: a) Left side


Q3: What is a balanced chemical equation?

a) An equation with equal reactants and products

b) An equation that lists all reactants and products

c) An equation that obeys the law of conservation of mass

d) An equation with equal coefficients for all substances

Answer: c) An equation that obeys the law of conservation of mass


Q4: In a combustion reaction, which of the following is typically a product?

a) Oxygen gas

b) Water

c) Fuel

d) Heat

Answer: b) Water


Q5: What type of reaction involves the exchange of ions between compounds?

a) Combination reaction

b) Decomposition reaction

c) Displacement reaction

d) Double displacement reaction

Answer: d) Double displacement reaction


Q6: Which of the following is an example of a decomposition reaction?

a) Burning wood

b) Mixing oil and water

c) Baking bread

d) Electrolysis of water

Answer: d) Electrolysis of water


Q7: In an exothermic reaction, energy is:

a) Absorbed from the surroundings

b) Released to the surroundings

c) Converted into light

d) Balanced

Answer: b) Released to the surroundings


Q8: What role does a catalyst play in a chemical reaction?

a) Increases the rate of the reaction

b) Decreases the rate of the reaction

c) Consumes reactants

d) Forms new products

Answer: a) Increases the rate of the reaction


Q9: The law of conservation of mass states that:

a) Mass can be created during a chemical reaction

b) Mass can be destroyed during a chemical reaction

c) Mass is conserved during a chemical reaction

d) Mass is converted into energy during a chemical reaction

Answer: c) Mass is conserved during a chemical reaction


Q10: Which type of reaction involves the transfer of electrons between reactants?

a) Combination reaction

b) Decomposition reaction

c) Displacement reaction

d) Redox reaction

Answer: d) Redox reaction


Q11: Corrosion of metals is an example of which type of reaction?

a) Combination reaction

b) Decomposition reaction

c) Displacement reaction

d) Redox reaction

Answer: d) Redox reaction


Q12: Which of the following is an example of a combustion reaction?

a) Rusting of iron

b) Ripening of fruit

c) Photosynthesis in plants

d) Burning of natural gas

Answer: d) Burning of natural gas


Q13: What happens in a double displacement reaction?

a) Atoms of one element replace those of another element

b) Ions exchange between two compounds to form new compounds

c) A single compound breaks down into simpler substances

d) Two or more substances combine to form a single product

Answer: b) Ions exchange between two compounds to form new compounds


Q14: The number of atoms of each element is balanced in a:

a) Chemical reaction

b) Unbalanced equation

c) Incomplete equation

d) Neutralization reaction

Answer: a) Chemical reaction


Q15: Which type of reaction involves the breakdown of a single compound into two or more simpler substances?

a) Combination reaction

b) Decomposition reaction

c) Displacement reaction

d) Redox reaction

Answer: b) Decomposition reaction


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