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Science lesson plan · 10th grade (Year 11 in England) · 45 minutes

Reaction profiles: energy change and activation energy

Chemical reactions, acids and bases

CCSS NGSS.HS-PS1-4England: GCSE Combined Science: Energy changes

Objective and success criteria

Students will: Reaction profiles: energy change and activation energy.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Exothermic and endothermic reactions

Leads to: Predict how an equilibrium shifts (Le Chatelier); Calculate energy changes from bond energies

Materials: Teacher demo or video, Indicator color chart, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 5 min

  • Quick retrieval from earlier learning (Exothermic and endothermic reactions). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Is this exothermic or endothermic: photosynthesis? (exothermic / endothermic) → endothermicPrompt: Does it give out heat or take heat in?
  2. The temperature of a reaction mixture changes from 21 °C to 17 °C. What is the temperature change? (Use a minus sign for a fall.) → -4 °CPrompt: Change = final temperature − starting temperature.
  3. In an exothermic reaction, the energy of the products is… (exactly the same as the reactants / zero / lower than the energy of the reactants / higher than the energy of the reactants) → lower than the energy of the reactantsPrompt: Energy has been given out to the surroundings.

Hook · 5 min

  • Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
  • Share the objective: Reaction profiles: energy change and activation energy. Read the success criteria together.

I do: model it · 10 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: On a reaction profile, the reactants are at 80 kJ, the peak is at 220 kJ and the products are at 140 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.)
  • Step 1: 140 − 80 = 60
  • Step 2: Positive: energy is taken in (endothermic).
  • Step 3: So the answer is: 60 kJ
  • Answer: 60 kJ
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 10 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. On a reaction profile, the reactants are at 100 kJ, the peak is at 140 kJ and the products are at 70 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.) → -30 kJPrompt: energy change = energy of products − energy of reactants
  2. Reactants: 110 kJ. Peak of the profile: 235 kJ. Products: 145 kJ. What is the activation energy, in kJ? → 125 kJPrompt: Activation energy is the minimum energy needed to start the reaction.

You do: independent practice · 10 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 5 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. On a reaction profile, the reactants are at 50 kJ, the peak is at 90 kJ and the products are at -10 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.) → -60 kJPrompt: energy change = energy of products − energy of reactants
  2. Self-heating cans for camping use a reaction between calcium oxide and water. What type of reaction is this? (exothermic / endothermic / electrolysis / thermal decomposition) → exothermicPrompt: The can gets hot.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Exothermic and endothermic reactions.
  • Use concrete materials: teacher demo or video.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Move on to: Predict how an equilibrium shifts (Le Chatelier); Calculate energy changes from bond energies.
  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-10.

Free lesson plan from eurekami.com/lesson-plan-builder

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Reaction profiles: energy change and activation energy

Name

Date

Score/ 8

  1. Question 1

    On a reaction profile, the reactants are at 50 kJ, the peak is at 190 kJ and the products are at 70 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.)

    AnswerkJ

  2. Question 2

    On a profile, the products are higher than the reactants. What kind of reaction is it?

    • A. endothermic
    • B. exothermic
    • C. combustion
    • D. neutralisation

  3. Question 3

    Reactants: 90 kJ. Peak of the profile: 215 kJ. Products: 125 kJ. What is the activation energy, in kJ?

    AnswerkJ

  4. Question 4

    On a reaction profile, the reactants are at 100 kJ, the peak is at 160 kJ and the products are at 70 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.)

    AnswerkJ

  5. Question 5

    How does a catalyst change a reaction profile?

    • A. It raises the products
    • B. It lowers the peak (activation energy) but not the overall energy change
    • C. It removes the reactants
    • D. It changes an exothermic reaction into an endothermic one

  6. Question 6

    Reactants: 60 kJ. Peak of the profile: 160 kJ. Products: 95 kJ. What is the activation energy, in kJ?

    AnswerkJ

  7. Question 7

    On a reaction profile, the reactants are at 100 kJ, the peak is at 220 kJ and the products are at 160 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.)

    AnswerkJ

  8. Question 8

    Reactants: 40 kJ. Peak of the profile: 140 kJ. Products: 10 kJ. What is the activation energy, in kJ?

    AnswerkJ

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Answer key: Reaction profiles: energy change and activation energy

  1. 1. 20 kJ

  2. 2. A. endothermic

  3. 3. 125 kJ

  4. 4. -30 kJ

  5. 5. B. It lowers the peak (activation energy) but not the overall energy change

  6. 6. 100 kJ

  7. 7. 60 kJ

  8. 8. 100 kJ