Chemistry Lesson Note On Chemical Reactions and Types – Combination, Decomposition, Displacement

Topic: Chemical Reactions and Types – Combination, Decomposition, Displacement

Class: SS1

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Specific Objectives:

By the end of this lesson, students should be able to:

1. Define a chemical reaction.
2. Identify signs of a chemical reaction.
3. List and explain different types of chemical reactions.
4. Write balanced chemical equations for each type.
5. Differentiate between physical and chemical changes.

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Instructional Materials:

• Chart showing types of chemical reactions
• Samples or video demonstrations (e.g., vinegar + baking soda, rusting, burning magnesium)
• Test tubes, chemicals (safe for classroom use)
• Whiteboard and markers

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Lesson Content:

Step 1: Meaning of Chemical Reactions

• A chemical reaction is a process in which one or more substances (reactants) are changed into new substances (products) with different properties.

• It involves the breaking and forming of chemical bonds.

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Step 2: Signs of a Chemical Reaction

• Change in color
• Evolution of gas
• Formation of a precipitate
• Change in temperature (heat absorbed or released)
• Change in odor or production of light

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Step 3: Types of Chemical Reactions

1. Combination (or Synthesis) Reaction
   • Two or more substances combine to form a single product.
   • General form: A + B → AB
   • Example:

     2Mg + O_2 → 2MgO

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2. Decomposition Reaction
   • A single compound breaks down into two or more simpler substances.
   • General form: AB → A + B
   • Example:

     2H_2O_2 → 2H_2O + O_2

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3. Displacement (or Substitution) Reaction
   • A more reactive element replaces a less reactive one in a compound.
   • General form: A + BC → AC + B
   • Example:

     Zn + CuSO_4 → ZnSO_4 + Cu

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4. Double Displacement (or Metathesis) Reaction (Optional extension)
   • Two compounds exchange ions to form two new compounds.
   • General form: AB + CD → AD + CB
   • Example:

     NaCl + AgNO_3 → NaNO_3 + AgCl↓

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Step 4: Differences Between Physical and Chemical Changes

Physical Change	Chemical Change
No new substance is formed	New substances are formed
Usually reversible	Usually irreversible
Examples: melting, boiling	Examples: rusting, combustion

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Evaluation:

1. What is a chemical reaction?
2. Mention three signs that a chemical reaction has taken place.
3. Write and balance an equation for a decomposition reaction.
4. Distinguish between combination and displacement reactions.
5. Differentiate between physical and chemical changes with examples.

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Homework:

1. Classify the following as combination, decomposition, or displacement reactions:
   a)
   b)
   c)

2. Explain what happens when iron nails are placed in copper(II) sulfate solution.

3. State one real-life example of each type of chemical reaction.

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Conclusion:

Chemical reactions play a vital role in our daily lives—from the food we digest to the fuel we burn. Understanding the types of reactions helps us predict and explain many natural and industrial processes.