• 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: an instant cold pack? (exothermic / endothermic) → endothermicPrompt: Does it give out heat or take heat in?
2. The temperature of a reaction mixture changes from 22 °C to 29 °C. What is the temperature change? (Use a minus sign for a fall.) → 7 °CPrompt: Change = final temperature − starting temperature.
3. What is activation energy? (the energy in a battery / the energy given out by a reaction / the energy of light / the minimum energy particles need to react when they collide) → the minimum energy particles need to react when they collidePrompt: Why does a match need to be struck before it burns?

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

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: A reaction produces 150 cm³ of gas in 50 seconds. What is the mean rate of reaction, in cm³/s?
• Step 1: 150 ÷ 50 = 3
• Step 2: So the answer is: 3 cm³/s
• Answer: 3 cm³/s
• 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. A reaction produces 150 cm³ of gas in 60 seconds. What is the mean rate of reaction, in cm³/s? → 2.5 cm³/sPrompt: mean rate = amount of product ÷ time
2. Why does powdered marble react faster with acid than marble chips? (Powder has more mass / Powder is a different substance / Powder has a larger surface area, so there are more collisions / Chips are hotter) → Powder has a larger surface area, so there are more collisionsPrompt: Cutting something up exposes more of it.

• 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. Why does increasing the temperature speed up a reaction? (It adds more particles / It lowers the activation energy / Particles move faster, collide more often and more collisions have enough energy / Particles get bigger) → Particles move faster, collide more often and more collisions have enough energyPrompt: Think about collision theory.
2. Rates of reaction: which statement is NOT true? (Food lasts longer in a fridge because reactions are slower at low temperature. / Every collision between particles causes a reaction. / Increasing surface area increases the rate. / A catalyst is not used up in a reaction.) → Every collision between particles causes a reaction.Prompt: What does a catalyst change, and what does it not change?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.