Types of Chemical Reactions

In this chapter, we will explore different types of chemical reactions. We know that during chemical reactions, atoms break and make bonds to form new substances. Let's dive into the main types of chemical reactions: combination, decomposition, displacement, and double displacement reactions.

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1. Combination Reaction

A combination reaction occurs when two or more substances combine to form a single product.

Key Point:

• In a combination reaction, reactants combine to form one product.

Example Activity:

• Materials Needed: Calcium oxide (CaO), water (H₂O), beaker.

Instructions:

1. Take a small amount of calcium oxide in a beaker.
2. Slowly add water.
3. Carefully touch the beaker's surface.

Observations: You will feel that the beaker becomes warm. This indicates that heat is released during the reaction.

Chemical Equation: $\text{CaO}(s) + \text{H}\_2O(l) \rightarrow \text{Ca(OH)}\_2(aq) + \text{Heat}$

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2. Decomposition Reaction

Decomposition reactions occur when a single reactant breaks down into two or more simpler products.

Key Point:

• A single compound breaks down into simpler substances.

Example Activity:

• Materials Needed: Ferrous sulphate (FeSO₄), boiling tube, burner.

Instructions:

1. Take about 2 g of ferrous sulphate in a boiling tube.
2. Heat the boiling tube over a flame.
3. Observe the color change.

Observations: The green color of ferrous sulphate fades as it decomposes and emits a characteristic smell.

Chemical Equation: $2\text{FeSO}\_4(s) \rightarrow \text{Fe}\_2\text{O}\_3(s) + \text{SO}\_2(g) + \text{SO}\_3(g)$

Additional Example:

• Decomposition of calcium carbonate: $\text{CaCO}\_3(s) \rightarrow \text{CaO}(s) + \text{CO}\_2(g)$

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3. Displacement Reaction

In a displacement reaction, an element in a compound is replaced by another element.

Key Point:

• An element displaces another in a compound.

Example Activity:

• Materials Needed: Iron nails, copper sulphate solution (CuSO₄), test tubes.

Instructions:

1. Clean three iron nails.
2. Place one nail in test tube (A) and tie two nails in a thread to immerse in test tube (B) containing copper sulphate for 20 minutes.
3. Remove and compare results.

Observations: In test tube (B), the blue color of the copper sulphate fades as copper is deposited onto the iron nails, indicating a displacement reaction.

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4. Double Displacement Reaction

In double displacement reactions, the ions of two compounds exchange places to form two new compounds.

Key Points:

• Exchange of ions occurs between two reactants.

Example: When you mix lead(II) nitrate and potassium iodide, a white precipitate of lead iodide forms while potassium nitrate remains in solution.

Chemical Equation: $\text{Pb(NO}\_3)\_2(aq) + \text{2KI}(aq) \rightarrow \text{PbI}\_2(s) + \text{2KNO}\_3(aq)$

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Scenario Based Questions

1. Scenario: Your friend is confused about combination and decomposition reactions.

   • Question: How can you explain the difference?
   • Answer: A combination reaction forms a single product from multiple reactants, while decomposition breaks down a compound into simpler products.

2. Scenario: You are conducting an experiment with iron nails and copper sulphate.

   • Question: What do you predict will happen to the blue color of the solution?
   • Answer: The blue color will fade as iron displaces copper, leading to the deposition of copper on the nails.

3. Scenario: You are discussing real-life applications of decomposition reactions.

   • Question: Can you give an example of where decomposition is useful?
   • Answer: The decomposition of calcium carbonate is crucial in cement production.

4. Scenario: You want to describe the energy changes in decomposition reactions.

   • Question: Why do these reactions often require heat or light?
   • Answer: Decomposition reactions require energy input to break chemical bonds, making them endothermic.

5. Scenario: Your science club is experimenting with chemical reactions.

   • Question: How would you classify the reactions between chemical ions?
   • Answer: They can be classified as double displacement reactions as ions are exchanged to form new compounds.

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