Science lesson plan · 11th grade (Year 12 in England) · 45 minutes
Calculate energy changes from bond energies
Chemical reactions, acids and bases
CCSS NGSS.HS-PS1-4England: GCSE Combined Science: Energy changes (bond energies, Higher)
Objective and success criteria
Students will: Calculate energy changes from bond energies.
- 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
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). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- On a reaction profile, the reactants are at 50 kJ, the peak is at 185 kJ and the products are at 125 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.) → 75 kJPrompt: energy change = energy of products − energy of reactants
- Reactants: 140 kJ. Peak of the profile: 190 kJ. Products: 110 kJ. What is the activation energy, in kJ? → 50 kJPrompt: Activation energy is the minimum energy needed to start the reaction.
- On a profile, the products are higher than the reactants. What kind of reaction is it? (endothermic / combustion / exothermic / neutralisation) → endothermicPrompt: Energy has been taken in from 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: Calculate energy changes from bond energies. 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: CH₄ + 2O₂ → CO₂ + 2H₂O. Bond energies (kJ/mol): C–H 413, O=O 498, C=O 805, O–H 464. Calculate the energy change, in kJ/mol.
- Step 1: broken: 4 × 413 + 2 × 498 = 2648
- Step 2: made: 2 × 805 + 4 × 464 = 3466
- Step 3: 2648 − 3466 = −818
- Step 4: So the answer is: −818 kJ/mol
- Answer: -818 kJ/mol
- 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.
- CH₄ + 2O₂ → CO₂ + 2H₂O. Bond energies (kJ/mol): C–H 413, O=O 498, C=O 805, O–H 464. Calculate the energy change, in kJ/mol. → -818 kJ/molPrompt: energy change = energy to break bonds − energy released making bonds
- In a reaction, 1750 kJ is needed to break bonds and 1450 kJ is released when new bonds form. Is the reaction exothermic or endothermic? (exothermic / endothermic) → endothermicPrompt: Breaking bonds takes in energy; making bonds releases it.
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.
- H₂ + Br₂ → 2HBr. Bond energies (kJ/mol): H–H 436, Br–Br 193, H–Br 366. Calculate the energy change, in kJ/mol. → -103 kJ/molPrompt: energy change = energy to break bonds − energy released making bonds
- In a reaction, 600 kJ is needed to break bonds and 300 kJ is released when new bonds form. Is the reaction exothermic or endothermic? (exothermic / endothermic) → endothermicPrompt: Breaking bonds takes in energy; making bonds releases it.
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-11.
Free lesson plan from eurekami.com/lesson-plan-builder