• Quick retrieval from earlier learning (The particle model). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Which state is described: particles in fixed positions that only vibrate? (solid / liquid / gas) → solidPrompt: How close are the particles, and how do they move?
2. Why can't solids flow? (Their particles move very fast / Their particles do not exist / Their particles are far apart / Their particles are held in fixed positions) → Their particles are held in fixed positionsPrompt: Can solid particles swap places?
3. The particle model: which statement is NOT true? (The particles in ice are a different substance from the particles in water. / All matter is made of tiny particles. / Particles in a solid still vibrate. / Particles in a gas are much further apart than in a liquid.) → The particles in ice are a different substance from the particles in water.Prompt: Do particles themselves change size?

• Show an ice cube melting and a kettle steaming and ask what is the same and what is different.
• Share the objective: Gas laws: pressure, volume and temperature. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: A gas at 200 kPa occupies 24 cm³. At constant temperature it is compressed to 12 cm³. What is its new pressure, in kPa?
• Step 1: p₂ = 200 × 24 ÷ 12 = 400
• Step 2: So the answer is: 400 kPa
• Answer: 400 kPa
• 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 gas at 120 kPa occupies 36 cm³. At constant temperature it is compressed to 18 cm³. What is its new pressure, in kPa? → 240 kPaPrompt: At constant temperature, p₁V₁ = p₂V₂.
2. A gas occupies 20 cm³ at 27 °C. At constant pressure it is heated to 327 °C. What is its new volume, in cm³? (Use kelvin: K = °C + 273.) → 40 cm³Prompt: Convert both temperatures to kelvin first.

• 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. A gas at 100 kPa occupies 24 cm³. At constant temperature it is compressed to 12 cm³. What is its new pressure, in kPa? → 200 kPaPrompt: At constant temperature, p₁V₁ = p₂V₂.
2. A sealed can contains gas at 240 kPa and 280 K. It is heated to 300 K. What is the new pressure, in kPa? Give 1 decimal place. → 257.1 kPaPrompt: At constant volume, p ÷ T stays the same.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-12.