• Quick retrieval from earlier learning (Reactants, products and word equations). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Complete the word equation: magnesium + oxygen → ___ (carbon dioxide / zinc oxide / magnesium oxide / magnesium chloride) → magnesium oxidePrompt: A metal reacting with oxygen makes a metal oxide.
2. In the reaction "iron + sulfur → iron sulfide", what are the reactants? (iron only / iron sulfide / sulfur and iron sulfide / iron and sulfur) → iron and sulfurPrompt: Reactants are on the left of the arrow.
3. Word equations: which statement is NOT true? (The arrow in a word equation means "equals". / Reactants are written on the left of the arrow. / Thermal decomposition breaks a substance down using heat. / Incomplete combustion can produce carbon monoxide, a poisonous gas.) → The arrow in a word equation means "equals".Prompt: Which side of the arrow is which?

• Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
• Share the objective: Exothermic and endothermic reactions. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Is this exothermic or endothermic: thermal decomposition of calcium carbonate?
• Step 1: Endothermic reactions take in energy from the surroundings, so the temperature falls.
• Step 2: So the answer is: endothermic
• Answer: endothermic
• 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. Is this exothermic or endothermic: thermal decomposition of calcium carbonate? (exothermic / endothermic) → endothermicPrompt: Does it give out heat or take heat in?
2. The temperature of a reaction mixture changes from 20 °C to 32 °C. What is the temperature change? (Use a minus sign for a fall.) → 12 °CPrompt: Change = final temperature − starting temperature.

• 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 6 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. The temperature of a reaction mixture changes from 20 °C to 5 °C. What is the temperature change? (Use a minus sign for a fall.) → -15 °CPrompt: Change = final temperature − starting temperature.
2. What is activation energy? (the energy in a battery / the energy given out by a reaction / the minimum energy particles need to react when they collide / the energy of light) → the minimum energy particles need to react when they collidePrompt: Why does a match need to be struck before it burns?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-8.