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Detailed notes on Thermal Physics for Cambridge IGCSE Coordinated Science, covering key concepts, explanations, examples, and exam-focused revision points.
Changes of state involve latent heat (energy absorbed or released with no temperature change). Cambridge tests melting, boiling, evaporation, condensation, and the energy involved — along with specific heat capacity.
Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).
Q = mcΔT links heat energy, mass, material, and temperature change.
Specific heat capacity (c):
The energy required to raise the temperature of 1 kg of a substance by 1°C (or 1 K). Q = mcΔT
Typical values:
| Material | c (J/kg°C) |
|---|---|
| Water | 4200 |
| Aluminium | 900 |
| Iron | 450 |
| Copper | 400 |
Why water has high c:
Example: How much energy is needed to heat 2 kg of water from 20°C to 100°C?
Q = 2 × 4200 × 80 = 672 000 J = 672 kJ
Experimental measurement:
During a state change, energy is absorbed/released but temperature stays constant.
Specific latent heat (L):
The energy absorbed or released when 1 kg of a substance changes state at constant temperature. Q = mL
Types:
Why temperature is constant during state change:
Heating/cooling curve:
Evaporation vs Boiling:
| Feature | Evaporation | Boiling |
|---|---|---|
| Temperature | Below boiling point | At boiling point only |
| Location | Surface only | Throughout the liquid |
| Cooling effect | Yes (liquid cools) | No net cooling of remaining liquid |
| Rate affected by | Temperature, surface area, wind | Fixed by boiling point |
Cooling by evaporation:
Verbatim phrases and definitions Cambridge mark schemes credit.
Paper 4: 'Calculate the energy to melt 0.5 kg of ice. Latent heat of fusion = 336 000 J/kg' (2 marks — Q = 0.5 × 336 000 = 168 000 J). 'Explain why sweating cools the body' (2 marks — fast-moving water molecules evaporate from skin surface; remaining molecules have lower average KE → temperature falls). 'A heating curve shows a horizontal section. Explain what is happening' (2 marks — state change; energy absorbed breaking intermolecular bonds without raising temperature). 'Calculate Q to heat 3 kg of water by 40°C' (2 marks — Q = 3 × 4200 × 40 = 504 000 J).
Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (P3); 0654 Examiner Reports 2022-2024. Last reviewed 2026-05-14.
Step-by-step solutions to past-paper-style questions on matter and thermal properties , written exactly the way a tutor would explain them at the board.
Question
Calculate the energy required to heat 2.0kg of water from 20°C to 80°C. The specific heat capacity of water is 4200J/(kg°C).
Step-by-step solution
Step 1
Identify variables: m=2.0kg; Δθ=80−20=60°C; c=4200J/(kg°C).
Step 2
Apply Q=mcΔθ.
Q=2.0×4200×60=504000J=504kJ
Answer
Q=504kJ
Question
Ice at 0°C is melted and then heated to 100°C. The mass of ice is 0.50kg. Calculate the total energy required. Specific latent heat of fusion of ice =336000J/kg; specific heat capacity of water =4200J/(kg°C).
Step-by-step solution
Step 1
Energy to melt the ice (latent heat).
Q1=mL=0.50×336000=168000J
Step 2
Energy to heat water from 0 to 100°C.
Q2=mcΔθ=0.50×4200×100=210000J
Step 3
Total energy.
Q=Q1+Q2=168000+210000=378000J
Answer
Q=378000J=378kJ
Examiner tip
Two separate stages must be calculated and added. Do not forget the latent heat stage — temperature does not change during melting.
Question
Sketch and annotate a heating curve for a substance heated at constant rate from below its melting point to above its boiling point. Explain what is happening at each stage in terms of particle energy.
Step-by-step solution
Step 1
Stage 1 (solid heating): Temperature rises as particles gain kinetic energy, vibrating more vigorously.
Step 2
Stage 2 (melting plateau at Tmelt): Temperature stays constant. Energy input goes into breaking intermolecular bonds (increasing potential energy), not kinetic energy. The graph is horizontal.
Step 3
Stage 3 (liquid heating): Temperature rises again as particles gain kinetic energy.
Step 4
Stage 4 (boiling plateau at Tboil): Temperature stays constant. Energy goes into completely separating particles (liquid → gas). The graph is horizontal again.
Step 5
Stage 5 (gas heating): Temperature rises as gas particles speed up.
Answer
Heating curve has two horizontal plateaux at melting point and boiling point, where energy is used to increase particle potential energy (break bonds) rather than kinetic energy (temperature).
The formulae you need to memorise for matter and thermal properties on the Cambridge IGCSE 0654 paper, with every variable defined in plain English and a note on when to use it.
Q=mcΔθ
When to use
Calculating energy transferred to change an object's temperature (no state change).
Q=mL
When to use
Calculating energy transferred during a change of state (temperature constant).
Definitions to memorise and the exact keywords mark schemes credit for matter and thermal properties answers — sharpened from recent examiner reports for the 2026 0654 sitting.
The energy required to raise the temperature of 1kg of a substance by 1°C (or 1K). SI unit: J/(kg°C) or J/(kgK).
The energy required to change the state of 1kg of a substance without changing its temperature. Fusion (melting/freezing) or vaporisation (boiling/condensing).
The change of state from liquid to gas occurring at the surface of a liquid at any temperature, as high-energy molecules escape. It causes cooling of the remaining liquid.
Related: boiling
The change of state from liquid to gas throughout the bulk of the liquid at a fixed temperature (the boiling point), where vapour bubbles form within the liquid.
Related: evaporation
The traps other students keep falling into on matter and thermal properties questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.
Why it happens
Students only apply Q=mcΔθ for the entire temperature range.
How to avoid it
If the substance changes state, split into separate stages: (1) heating to transition temperature, (2) state change (Q=mL), (3) heating from transition temperature.
Why it happens
Both convert liquid to gas, so students treat them identically.
How to avoid it
Evaporation: surface only, any temperature, cools liquid, no bubbles. Boiling: throughout liquid, specific temperature, bubbles form inside liquid.
Why it happens
Students plug in the final temperature without subtracting the initial temperature.
How to avoid it
Δθ=Tfinal−Tinitial. Always subtract the initial temperature, not just use the final value.
The things students keep getting wrong in this sub-topic, answered.