• 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 20 °C to 41 °C. What is the temperature change? (Use a minus sign for a fall.) → 21 °CPrompt: Change = final temperature − starting temperature.
3. In an exothermic reaction, the energy of the products is… (lower than the energy of the reactants / exactly the same as the reactants / higher than the energy of the reactants / zero) → lower than the energy of the reactantsPrompt: Energy has been given out to the surroundings.

• 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.

• 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.

• 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 50 kJ, the peak is at 170 kJ and the products are at -40 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.) → -90 kJPrompt: energy change = energy of products − energy of reactants
2. Reactants: 60 kJ. Peak of the profile: 210 kJ. Products: 30 kJ. What is the activation energy, in kJ? → 150 kJPrompt: Activation energy is the minimum energy needed to start the reaction.

• 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.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. Reactants: 140 kJ. Peak of the profile: 210 kJ. Products: 110 kJ. What is the activation energy, in kJ? → 70 kJPrompt: Activation energy is the minimum energy needed to start the reaction.
2. Why does a mixture of methane and air not burn until a spark is added? (Methane is endothermic / The spark adds oxygen / The spark removes carbon dioxide / The spark provides the activation energy) → The spark provides the activation energyPrompt: Reactions need a minimum energy to start.

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