Chemistry Lesson Note On Energy Changes in Reactions – Endothermic and Exothermic

Topic: Energy Changes in Reactions – Endothermic and Exothermic

Class: SS1

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Specific Objectives:

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

1. Define energy changes in chemical reactions.
2. Differentiate between exothermic and endothermic reactions.
3. Provide examples of both types of reactions.
4. Illustrate energy profile diagrams for endothermic and exothermic reactions.
5. Explain the significance of energy changes in everyday life.

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Instructional Materials:

• Diagrams of energy profile graphs
• Samples or video demonstrations (e.g., dissolving ammonium chloride, combustion of candle wax)
• Charts or flashcards showing exothermic and endothermic processes
• Laboratory thermometer, beakers, test tubes, water, salts

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Lesson Content:

Step 1: Introduction to Energy Changes in Reactions

• Energy change refers to the absorption or release of heat during a chemical reaction.
• All chemical reactions involve the breaking of old bonds and the formation of new ones.
• These processes either absorb or release energy in the form of heat.

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Step 2: Exothermic Reactions

• Definition: Reactions that release heat energy to the surroundings.
• Surroundings become warmer.
• Examples:
  • Combustion of fuels:

    CH_4 + 2O_2 → CO_2 + 2H_2O + \text{heat}

    HCl + NaOH → NaCl + H_2O + \text{heat}

    C_6H_{12}O_6 + 6O_2 → 6CO_2 + 6H_2O + \text{energy}

• Energy profile diagram:
  • Reactants have more energy than products.
  • A curve going down, with energy released shown.

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Step 3: Endothermic Reactions

• Definition: Reactions that absorb heat energy from the surroundings.
• Surroundings become cooler.
• Examples:
  • Photosynthesis:

    6CO_2 + 6H_2O + \text{sunlight energy} → C_6H_{12}O_6 + 6O_2

• Thermal decomposition:

    CaCO_3 → CaO + CO_2

• Energy profile diagram:
  • Products have more energy than reactants.
  • A curve going up, showing energy absorbed.

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Step 4: Importance of Energy Changes

• Used in cooking, heating, and powering engines (exothermic)
• Cold packs for injuries (endothermic)
• Industrial processes (e.g., cement production, refrigeration)

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Evaluation:

1. Define exothermic and endothermic reactions.
2. Give two examples each of endothermic and exothermic reactions.
3. Draw an energy profile diagram for an exothermic reaction.
4. What type of reaction is photosynthesis? Why?
5. How is energy change important in everyday life?

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Homework:

1. Write a short note on the differences between exothermic and endothermic reactions.
2. Identify whether the following are exothermic or endothermic:
   a) Combustion of wood
   b) Decomposition of calcium carbonate
   c) Neutralization of acid with base
   d) Dissolution of potassium chloride
3. Explain how you would demonstrate an endothermic reaction using common classroom materials.

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Conclusion:

Understanding energy changes in reactions helps us to better control chemical processes in daily life, industry, and nature. Whether heat is given off or absorbed, energy is always conserved and plays a vital role in chemistry.