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Physics · Particle model of matter
Specific latent heat
Use \(E = mL\) to calculate the energy for a change of state, interpret heating and cooling graphs, and distinguish specific heat capacity from specific latent heat.
Teacher resources
The teacher copies: slides with the questions built in, the answers, and anything else attached to this lesson for whoever is teaching it.
- Specific latent heat - Teacher Slides.pptx Teacher The lesson slides with the teacher's notes on each slide, and every question and mark scheme built in. Built from the lesson script on 30 September 2026. View
- Specific latent heat - Teacher Notes.docx Teacher The complete notes with the teacher's notes and every model answer in full. Built from the lesson script on 30 September 2026. View
Student handouts
The same files the students see, to print or hand out.
- Specific latent heat.pptx Built from the lesson script on 30 September 2026. View
- Specific latent heat - Completed Notes.docx The full notes for the lesson, to revise from. Built from the lesson script on 30 September 2026. View
- Specific latent heat - Exam Questions.docx Built from the lesson script on 30 September 2026. View
Warm-up
Answer each one, then check.
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1
What happens to temperature during melting?
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It stays constant
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2
What is the unit of energy?
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Joule
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3
What is the equation for a temperature change?
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\(\Delta E = mc\Delta\theta\)
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4
Name the change from liquid to gas.
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Boiling / evaporating
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5
What is internal energy?
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Total kinetic and potential energy of the particles
Learning Objectives
- 1Define specific latent heat and distinguish fusion from vaporisation.
- 2Apply \(E = mL\).
- 3Interpret heating and cooling graphs that include changes of state.
- 4Distinguish specific heat capacity from specific latent heat.
SPECIFIC LATENT HEAT
The specific latent heat of a substance is the energy needed to change the state of 1 kg of the substance with no change in temperature.
\(E = mL\) is given on the equation sheet. Specific latent heat of fusion: solid to liquid. Specific latent heat of vaporisation: liquid to gas. L is in J/kg.
A Heating Curve
Flat sections show a change of state.
Two Different Ideas
Specific heat capacity
- Energy to raise the temperature of 1 kg by 1 °C.
- The temperature changes.
- \(\Delta E = mc\Delta\theta\); J/kg °C.
Specific latent heat
- Energy to change the state of 1 kg with no temperature change.
- The temperature stays the same.
- \(E = mL\); J/kg.
Melting Ice
Calculate the energy needed to melt 0.20 kg of ice at 0 °C. Specific latent heat of fusion of water = 334 000 J/kg.
Show the solutionHide the solution
- 1 Write the equation \(E = mL\)
- 2 Substitute \(E = 0.20 \times 334\,000\)
- 3 Answer \(E = 66\,800\) J
Answer66 800 J
Boiling Water
Calculate the energy to change 0.50 kg of water at 100 °C into steam. Specific latent heat of vaporisation = 2 260 000 J/kg.
Show the solutionHide the solution
- 1 Substitute \(E = 0.50 \times 2\,260\,000\)
- 2 Answer \(E = 1\,130\,000\) J
Answer1 130 000 J (1.13 MJ)
Reading the Graph
Explain why the temperature stays constant during section B of the heating curve.
Show the solutionHide the solution
- 1 Energy is still supplied The particles are gaining energy
- 2 Where it goes It increases the potential energy of the particles as the bonds are broken
- 3 So The average kinetic energy, and the temperature, stay the same
AnswerThe energy supplied breaks the bonds (changing potential energy) so the temperature does not rise.
Why Steam Burns More
A favourite exam idea.
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Condensing
Steam at 100 °C condenses to water at 100 °C and releases a lot of latent heat.
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Then
The water then cools and releases more energy.
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So
Steam transfers more energy to skin than boiling water at the same temperature.
Read the Curve
On a heating curve for water there are flat sections at 0 °C and 100 °C. Explain what is happening in each and why the second is longer.
1. Name each change.
2. Compare the latent heats.
A good answer shows: At 0 °C the ice is melting; at 100 °C the water is boiling. The boiling section is longer because the latent heat of vaporisation is much greater than the latent heat of fusion.
Can I...?
- 1State what specific latent heat is.
- 2Distinguish fusion from vaporisation.
- 3Use \(E = mL\).
- 4Read a heating curve.
- 5Explain flat sections.
- 6Distinguish c from L.
- 7Explain steam burns.
- 8Give units of L.
Summary & Exam Focus
- \(E = mL\).
- Temperature is constant during a change of state.
- Heating curves have flat sections at melting and boiling points.
- Distinguish c and L.
Exam focus
Calculate the energy needed to melt 0.35 kg of ice at 0 °C. Specific latent heat of fusion = 334 000 J/kg. (2 marks) (2 marks)
Multiply mass by L.
Key terms
The vocabulary this lesson expects you to use. Each one is linked from the first place it appears above.
- Specific latent heat
- Energy to change the state of 1 kg with no temperature change.
- Latent heat of fusion
- For solid to liquid.
- Latent heat of vaporisation
- For liquid to gas.
- Heating curve
- A temperature-time graph for a heated substance.
- Constant temperature
- Temperature that does not change during a change of state.
- Potential energy
- Energy stored due to the forces between particles.
Questions and answers
10 questions set on this lesson, with the mark schemes and model answers open.
Calculate the energy needed to melt 0.35 kg of ice at 0 °C. The specific latent heat of fusion of water is 334 000 J/kg. Use the equation: energy for a change of state = mass × specific latent heat
Mark scheme — 2 marks available
- Correct substitution — 1 mark
- 116 900 J — 1 mark
Model answer
\(0.35 \times 334\,000 = 116\,900\) J
The graph shows how the temperature of a solid changes as it is heated at a steady rate until it is a gas. (a) State the melting point. (b) What is happening between 2 and 8 minutes? (c) Explain why the temperature stays constant during this time.
Mark scheme — 4 marks available
- 0 °C — 1 mark
- Melting — 1 mark
- Energy used to break bonds or change potential energy — 1 mark
- Kinetic energy or temperature does not increase — 1 mark
Model answer
(a) 0 °C. (b) The solid is melting (changing state to liquid). (c) The energy supplied changes the potential energy of the particles (breaking bonds), not their kinetic energy, so the temperature does not rise.
Describe the difference between specific heat capacity and specific latent heat.
Mark scheme — 2 marks available
- Specific heat capacity: temperature change — 1 mark
- Specific latent heat: change of state, no temperature change — 1 mark
Model answer
Specific heat capacity is the energy needed to raise the temperature of 1 kg by 1 °C. Specific latent heat is the energy needed to change the state of 1 kg with no change in temperature.
Calculate the energy needed to change 0.50 kg of water at 100 °C into steam. The specific latent heat of vaporisation of water is 2 260 000 J/kg.
Mark scheme — 3 marks available
- Correct substitution — 1 mark
- 1 130 000 J — 1 mark
- Unit J — 1 mark
Model answer
\(0.50 \times 2\,260\,000 = 1\,130\,000\) J
Steam at 100 °C causes a more serious burn than boiling water at 100 °C. Explain why.
Mark scheme — 3 marks available
- Steam condenses on the skin — 1 mark
- Releases latent heat — 1 mark
- So more energy is transferred than from the water alone — 1 mark
Model answer
When steam condenses it releases a large amount of energy (latent heat) to the skin, in addition to the energy released as the water cools, so more energy is transferred to the skin.
During melting the temperature...
Why: The energy changes the state, not the temperature.
The unit of specific latent heat is...
Why: Joules per kilogram.
The energy to melt 2 kg with L = 300 000 J/kg is...
Why: 2 × 300 000.
A flat section on a heating curve shows...
Why: Energy is going into potential energy.
Latent heat of vaporisation refers to...
Why: Fusion is solid to liquid.