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

Predict how an equilibrium shifts (Le Chatelier)

Chemical reactions, acids and bases

CCSS NGSS.HS-PS1-6England: GCSE Combined Science: The rate and extent of chemical change (Higher)

Objective and success criteria

Students will: Predict how an equilibrium shifts (Le Chatelier).

  • 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: Reaction profiles: energy change and activation energy; Rates of reaction

Leads to: the next skill in this area.

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 (Reaction profiles: energy change and activation energy; Rates of reaction). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. On a reaction profile, the reactants are at 150 kJ, the peak is at 210 kJ and the products are at 130 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.) → -20 kJPrompt: energy change = energy of products − energy of reactants
  2. A reaction produces 50 cm³ of gas in 20 seconds. What is the mean rate of reaction, in cm³/s? → 2.5 cm³/sPrompt: mean rate = amount of product ÷ time
  3. Reactants: 110 kJ. Peak of the profile: 180 kJ. Products: 60 kJ. What is the activation energy, in kJ? → 70 kJPrompt: Activation energy is the minimum energy needed to start the reaction.

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: Predict how an equilibrium shifts (Le Chatelier). 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: All substances are gases in this equilibrium: Nâ‚‚Oâ‚„ ⇌ 2NOâ‚‚. The forward reaction is endothermic. The pressure is increased. What happens to the position of equilibrium?
  • Step 1: Higher pressure favours the side with fewer gas molecules.
  • Step 2: So the answer is: shifts left (more reactants)
  • Answer: shifts left (more reactants)
  • 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. All substances are gases in this equilibrium: N₂O₄ ⇌ 2NO₂. The forward reaction is endothermic. The temperature is increased. What happens to the position of equilibrium? (shifts right (more products) / shifts left (more reactants) / no change in position) → shifts right (more products)Prompt: The system shifts to oppose the change.
  2. Why does a closed system matter for equilibrium? (It keeps the system warm / It adds a catalyst / It makes the reaction irreversible / Nothing can enter or leave, so both reactions can balance) → Nothing can enter or leave, so both reactions can balancePrompt: What happens if a gaseous product escapes?

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. Why does a closed system matter for equilibrium? (It makes the reaction irreversible / Nothing can enter or leave, so both reactions can balance / It keeps the system warm / It adds a catalyst) → Nothing can enter or leave, so both reactions can balancePrompt: What happens if a gaseous product escapes?
  2. All substances are gases in this equilibrium: N₂O₄ ⇌ 2NO₂. The forward reaction is endothermic. Product is removed as it forms. What happens to the position of equilibrium? (shifts right (more products) / shifts left (more reactants) / no change in position) → shifts right (more products)Prompt: The system shifts to oppose the change.

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: Reaction profiles: energy change and activation energy.
  • 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

  • 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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Predict how an equilibrium shifts (Le Chatelier)

Name

Date

Score/ 8

  1. Question 1

    All substances are gases in this equilibrium: H₂ + I₂ ⇌ 2HI. The pressure is increased. What happens to the position of equilibrium?

    • A. shifts right (more products)
    • B. shifts left (more reactants)
    • C. no change in position

  2. Question 2

    Equilibrium: which statement is NOT true?

    • A. Equilibrium can only be reached in a closed system.
    • B. At equilibrium the concentrations of reactants and products are always equal.
    • C. If a reversible reaction is exothermic in one direction, it is endothermic in the other.
    • D. In the Haber process, increasing pressure increases the yield of ammonia.

  3. Question 3

    Why does a closed system matter for equilibrium?

    • A. It makes the reaction irreversible
    • B. Nothing can enter or leave, so both reactions can balance
    • C. It adds a catalyst
    • D. It keeps the system warm

  4. Question 4

    All substances are gases in this equilibrium: H₂ + I₂ ⇌ 2HI. Product is removed as it forms. What happens to the position of equilibrium?

    • A. shifts right (more products)
    • B. shifts left (more reactants)
    • C. no change in position

  5. Question 5

    What is true at dynamic equilibrium?

    • A. There are equal amounts of reactants and products
    • B. Both reactions have stopped
    • C. The forward and reverse reactions happen at the same rate
    • D. Only the forward reaction happens

  6. Question 6

    All substances are gases in this equilibrium: H₂ + I₂ ⇌ 2HI. More of the first reactant is added. What happens to the position of equilibrium?

    • A. shifts right (more products)
    • B. shifts left (more reactants)
    • C. no change in position

  7. Question 7

    All substances are gases in this equilibrium: CO + 2H₂ ⇌ CH₃OH. The forward reaction is exothermic. The pressure is decreased. What happens to the position of equilibrium?

    • A. shifts right (more products)
    • B. shifts left (more reactants)
    • C. no change in position

  8. Question 8

    All substances are gases in this equilibrium: N₂O₄ ⇌ 2NO₂. The forward reaction is endothermic. The temperature is decreased. What happens to the position of equilibrium?

    • A. shifts right (more products)
    • B. shifts left (more reactants)
    • C. no change in position

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Answer key: Predict how an equilibrium shifts (Le Chatelier)

  1. 1. C. no change in position

  2. 2. B. At equilibrium the concentrations of reactants and products are always equal.

  3. 3. B. Nothing can enter or leave, so both reactions can balance

  4. 4. A. shifts right (more products)

  5. 5. C. The forward and reverse reactions happen at the same rate

  6. 6. A. shifts right (more products)

  7. 7. B. shifts left (more reactants)

  8. 8. B. shifts left (more reactants)