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Science lesson plan · 11th grade (Year 12 in England) · 45 minutes

Specific latent heat (E = m L)

States of matter

CCSS NGSS.HS-PS3-1CCSS NGSS.HS-PS3-4England: GCSE Combined Science: Particle model of matter (specific latent heat)

Objective and success criteria

Students will: Specific latent heat (E = m L).

  • 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: Specific heat capacity and latent heat

Leads to: the next skill in this area.

Materials: Ice, water and a kettle (teacher demo), Particle diagrams, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 5 min

  • Quick retrieval from earlier learning (Specific heat capacity and latent heat). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. How much energy is needed to heat 2.5 kg of water by 15 °C? The specific heat capacity of water is 4200 J/kg °C. Give your answer in J. → 157500 JPrompt: Use ΔE = m × c × Δθ.
  2. A 4 kg block of aluminium (aluminum) absorbs 180000 J and its temperature rises by 50 °C. What is the specific heat capacity of aluminium (aluminum), in J/kg °C? → 900 J/kg°CPrompt: Rearrange ΔE = m × c × Δθ to find c.
  3. How much energy is needed to melt 0.25 kg of ice at 0 °C? The specific latent heat of fusion of water is 334 000 J/kg. Give your answer in J. → 83500 JPrompt: Use E = m × L.

Hook · 5 min

  • Show an ice cube melting and a kettle steaming and ask what is the same and what is different.
  • Share the objective: Specific latent heat (E = m L). 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: How much energy is needed to boil away 2 kg of water at 100 °C, in kJ? (Specific latent heat of vaporisation of water = 2260 kJ/kg)
  • Step 1: 2 × 2260 = 4520
  • Step 2: So the answer is: 4520 kJ
  • Answer: 4520 kJ
  • 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.
  1. How much energy is needed to melt 1.5 kg of ice at 0 °C, in kJ? (Specific latent heat of fusion of water = 334 kJ/kg) → 501 kJPrompt: E = m × L
  2. 41 kJ of energy melts or boils 0.2 kg of a substance with no change in temperature. What is its specific latent heat, in kJ/kg? → 205 kJ/kgPrompt: L = E ÷ m

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.
  1. 200 kJ of energy melts or boils 0.5 kg of a substance with no change in temperature. What is its specific latent heat, in kJ/kg? → 400 kJ/kgPrompt: L = E ÷ m
  2. Why does sweating cool you down, in terms of latent heat? (Sweat reflects sunlight / Evaporating sweat takes the latent heat it needs from your skin / Sweat is colder than blood / Sweat releases latent heat into the skin) → Evaporating sweat takes the latent heat it needs from your skinPrompt: Evaporation is a change of state that needs energy.

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: Specific heat capacity and latent heat.
  • Use concrete materials: ice, water and a kettle (teacher demo).
  • 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

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Specific latent heat (E = m L)

Name

Date

Score/ 8

  1. Question 1

    102.5 kJ of energy melts or boils 0.5 kg of a substance with no change in temperature. What is its specific latent heat, in kJ/kg?

    AnswerkJ/kg

  2. Question 2

    How much energy is needed to boil away 0.25 kg of water at 100 °C, in kJ? (Specific latent heat of vaporisation of water = 2260 kJ/kg)

    AnswerkJ

  3. Question 3

    Why is the latent heat of vaporisation of water much larger than its latent heat of fusion?

    • A. Boiling happens at a lower temperature
    • B. Melting needs more energy
    • C. Water vapour has no particles
    • D. Boiling separates particles completely; melting only loosens them

  4. Question 4

    2712 kJ of energy melts or boils 1.2 kg of a substance with no change in temperature. What is its specific latent heat, in kJ/kg?

    AnswerkJ/kg

  5. Question 5

    How much energy is needed to melt 0.1 kg of ice at 0 °C, in kJ? (Specific latent heat of fusion of water = 334 kJ/kg)

    AnswerkJ

  6. Question 6

    On a heating curve for ice, why does the temperature stay at 0 °C for a while?

    • A. Energy is breaking bonds between particles to melt the ice, not raising their kinetic energy
    • B. Energy is destroyed while melting
    • C. Ice cannot be heated
    • D. The heater has turned off

  7. Question 7

    167 kJ of energy melts or boils 0.5 kg of a substance with no change in temperature. What is its specific latent heat, in kJ/kg?

    AnswerkJ/kg

  8. Question 8

    How much energy is needed to boil away 0.5 kg of water at 100 °C, in kJ? (Specific latent heat of vaporisation of water = 2260 kJ/kg)

    AnswerkJ

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Answer key: Specific latent heat (E = m L)

  1. 1. 205 kJ/kg

  2. 2. 565 kJ

  3. 3. D. Boiling separates particles completely; melting only loosens them

  4. 4. 2260 kJ/kg

  5. 5. 33.4 kJ

  6. 6. A. Energy is breaking bonds between particles to melt the ice, not raising their kinetic energy

  7. 7. 334 kJ/kg

  8. 8. 1130 kJ