Energy in Reactions

Lesson Context

Subject Area: GCSE Science – Chemistry
Topic: Energy Changes in Chemical Reactions
Year Group: 11
Curriculum Reference: AQA GCSE Combined Science: Trilogy (8464), Section 5.5: Energy Changes
Focus Areas: Exothermic and endothermic reactions, activation energy, and energy transfer between chemical and thermal energy stores.

This lesson is designed for a low-ability GCSE class and focuses on making abstract ideas more concrete through engaging discussion, visual aids, and hands-on activities.

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Lesson Objectives

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

1. Define exothermic and endothermic reactions, and recall examples of each.
2. Explain what happens to the surroundings in terms of heating up or cooling down.
3. Describe energy transfer between chemical and thermal energy stores.
4. Interpret and label reaction profile diagrams with activation energy.

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Required Materials

• Teacher:

  • Interactive board/slides
  • Pre-drawn reaction profile diagrams
  • Thermometer(s)
  • Labels for sorting activity

• Students:

  • Exercise books
  • Pens/pencils
  • Laminated prompt cards with examples of reactions

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Lesson Activities

1. Starter Activity (5 mins)

Title: "Heat or Cool?"

• Greet the class and project the following prompt on the board:
  “When you light a candle or dissolve a pack of instant cold compress, what happens to the surroundings – do they get hotter or colder?”
• Ask students to brainstorm ideas in pairs for one minute. Select a few pairs to share their responses. Use simple cues to assess their prior knowledge, clarify misconceptions, and build curiosity for the lesson ahead.

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2. Model & Explain (15 mins)

Key Concepts: Exothermic, endothermic, activation energy, energy transfer

1. Exothermic reactions: Using a candle as an example, explain how chemical energy is converted into thermal energy, transferring heat to the surroundings.
   • Use a reaction profile diagram to demonstrate how energy is released. Highlight the "activation energy" as the minimum energy needed to start the reaction.
2. Endothermic reactions: Use the cold compress example to explain how thermal energy from the surroundings is absorbed and stored as chemical energy in the reaction.
   • Display another reaction profile diagram showing energy being taken in.

Engage the Class:

• Ask students:
  "Can anyone think of other examples of exothermic or endothermic reactions?"
  (Offer scaffolds and suggestions like combustion, photosynthesis, dissolving salt in water.)

Visual Aid:

• Illustrate with animated slides depicting energy flow arrows between chemical and thermal stores.

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3. Group Activity (15 mins)

Title: "Hot, Cold, or Both?"

• Split the class into 7 groups of 4 students.
• Each group will receive 6 laminated cards, each with an example reaction (e.g., burning fuel, dissolving salt, respiration, photosynthesis).
  Task:
• Sort the cards: Decide if the reaction is exothermic or endothermic.
• Explain why: Write one sentence for each card explaining what happens to the surroundings (heat up or cool down) and why, using energy transfer language.
  Teacher Role: During the task, move between groups and provide individual support as needed, checking for comprehension and helping them use keywords such as “energy transfer,” “chemical energy,” and “thermal energy.”

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4. Mini Experiment (10 mins)

Title: "Feel the Change!"

Setup:

• Each pair gets a cup of water, a metal spoon, a teaspoon of citric acid, and a tablespoon of bicarbonate of soda.

Task:

1. Dissolve the citric acid in the water.
2. Add bicarbonate of soda to the water.
3. Place a thermometer in the mixture and observe the temperature change.

Discussion Prompt:

• Ask students, "What kind of reaction occurred? Did the surroundings heat up or cool down? Why?" Guide them to categorise this as an endothermic reaction and explain that thermal energy was absorbed from the surroundings during the reaction.

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5. Quick Recap & Check Understanding (5 mins)

• Display a partial reaction profile diagram on the board.
  Task:
• Students must identify whether the reaction is exothermic or endothermic and draw an arrow to indicate the activation energy on the graph.
  Ask:
• “What happens to the surroundings in this reaction?”
• “Why is activation energy important?”

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6. Plenary Activity (5 mins)

Title: "Energy Changes Quiz"

• Use multiple-choice questions on the board to test key concepts. Students answer using mini whiteboards. Example questions:
  1. "Combustion is an example of a(n):
     (A) Endothermic reaction (B) Exothermic reaction (C) Neutral reaction."_
  2. "In an endothermic reaction, energy is transferred:
     (A) From the surroundings to the reaction (B) From the reaction to the surroundings."_

Provide instant feedback and correct misunderstandings. End the quiz with a collaborative cheer for effort.

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Homework

Task:
Research two real-world examples of exothermic and endothermic reactions, explain how they are used, and describe the energy changes involved.

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Differentiation Strategies

1. Scaffolded Support: Provide sentence starters for the group activity (e.g., “This reaction is exothermic/endothermic because _______.”).
2. Visual Prompts: Use colour-coded diagrams to reinforce key differences between exothermic and endothermic reactions.
3. Targeted Support: Regularly check in with lower-attaining students during activities to ensure understanding.

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Assessment for Learning

• Monitoring pair and group discussions for key terms and correct reasoning.
• Checking quiz answers on whiteboards to quickly assess class-wide understanding.
• Exit questions at the end of lesson:
  “What’s one thing you’ve learnt about exothermic or endothermic reactions?”

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Extension Task (for Higher Achievers)

For students who complete tasks early:

• Ask them to consider why activation energy is important for controlling chemical reactions, such as in cooking or industrial production.

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Teacher Reflection Post-Lesson

• Did the practical activity help solidify students’ ideas about energy transfer?
• Were students able to correctly identify reactions as exothermic or endothermic by the end of the lesson?
• What scaffolding strategies worked best for low-ability learners?

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General Notes

This lesson balances theory, hands-on exploration, and visual learning, with opportunities for continuous assessment. It is specifically designed to align with UK GCSE standards while engaging low-ability students through concrete, relatable examples.