Viewing as
Teaching this? The teacher view adds 2 files, the mark schemes and the model answers.
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.
Warm-up
Answer each one, then check.
-
1
What happens to temperature during melting?
Show answerHide answer
It stays constant
-
2
What is the unit of energy?
Show answerHide answer
Joule
-
3
What is the equation for a temperature change?
Show answerHide answer
\(\Delta E = mc\Delta\theta\)
-
4
Name the change from liquid to gas.
Show answerHide answer
Boiling / evaporating
-
5
What is internal energy?
Show answerHide answer
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.
-
Condensing
Steam at 100 °C condenses to water at 100 °C and releases a lot of latent heat.
-
Then
The water then cools and releases more energy.
-
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.
Practice questions
Have a go at each one before you open its answer.
-
Question 1 Calculate 2 marks
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
Show answerHide answer
Model answer
\(0.35 \times 334\,000 = 116\,900\) J
Mark scheme
- Correct substitution — 1 mark
- 116 900 J — 1 mark
-
Question 2 Use the graph 4 marks
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.
Show answerHide answer
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.
Mark scheme
- 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
-
Question 3 Distinguish 2 marks
Describe the difference between specific heat capacity and specific latent heat.
Show answerHide answer
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.
Mark scheme
- Specific heat capacity: temperature change — 1 mark
- Specific latent heat: change of state, no temperature change — 1 mark
-
Question 4 Calculate 3 marks
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.
Show answerHide answer
Model answer
\(0.50 \times 2\,260\,000 = 1\,130\,000\) J
Mark scheme
- Correct substitution — 1 mark
- 1 130 000 J — 1 mark
- Unit J — 1 mark
-
Question 5 Explain 3 marks
Steam at 100 °C causes a more serious burn than boiling water at 100 °C. Explain why.
Show answerHide answer
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.
Mark scheme
- Steam condenses on the skin — 1 mark
- Releases latent heat — 1 mark
- So more energy is transferred than from the water alone — 1 mark
Quick check
-
During melting the temperature...
Show answerHide answer
A: stays constant
The energy changes the state, not the temperature.
-
The unit of specific latent heat is...
Show answerHide answer
B: J/kg
Joules per kilogram.
-
The energy to melt 2 kg with L = 300 000 J/kg is...
Show answerHide answer
C: 600 000 J
2 × 300 000.
-
A flat section on a heating curve shows...
Show answerHide answer
D: a change of state
Energy is going into potential energy.
-
Latent heat of vaporisation refers to...
Show answerHide answer
A: liquid to gas
Fusion is solid to liquid.
Downloads
Free to keep, print and annotate.
- 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
Something here looks wrong?
Tell us what and we will go and look. It goes to whoever writes these pages, nobody else, and we do not ask who you are — so there is nothing to sign and nothing comes back to you.