Free Melting, boiling & evaporation questions for IGCSE Physics (0625), part of Thermal physics. Each question has the answer and the marking points an examiner would look for.
Generate a full Melting, Boiling & Evaporation worksheet →All Thermal physics questionsWhat is the energy needed to change 0.4 kg of ice at 0 °C into water at 40 °C?
(specific latent heat of fusion of ice = 3.34 × 105 J/kg; specific heat capacity of water = 4200 J/(kg °C))
Answer: C
Which statement describes melting point?
Answer: D
An electric kettle has a power of 2000 W. It contains 0.8 kg of water at 25 °C. The specific heat capacity of water is 4200 J/(kg °C) and the specific latent heat of vaporisation of water is 2.26 × 106 J/kg. Assume that all the energy supplied is transferred to the water.
Calculate the time taken for the water to reach its boiling point.
The kettle does not switch off. Calculate the extra time needed for 0.05 kg of the water to boil away.
The temperature of the water does not rise while it is boiling, even though energy is still being supplied. Explain why.
In a real test the water takes 145 s to reach boiling point. Calculate the efficiency of the kettle.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 126 s E = mcΔθ = 0.8 × 4200 × 75 C1 = 2.52 × 105 J; t = E ÷ P C1 126 A1 | 3 |
| (b) | 56.5 s E = mL = 0.05 × 2.26 × 106 C1 56.5 A1 | 2 |
| (c) | Energy is used to break the forces/bonds between molecules (increase potential energy), not to increase their kinetic energy energy used to overcome forces of attraction between molecules B1 average kinetic energy of molecules (and so temperature) does not change B1 | 2 |
| (d) | 87% useful energy ÷ total energy = 2.52 × 105 ÷ (2000 × 145) C1 87 A1 | 2 |
This question is about changes of state.
Describe the arrangement and motion of particles in a solid and in a liquid.
A beaker of ice is heated steadily. Explain why the temperature stays at 0 °C while the ice melts.
State two differences between boiling and evaporation.
Explain, in terms of particles, why evaporation cools the liquid that is left.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | solid: regular, vibrate in fixed positions; liquid: close, irregular, move past each other solid: particles close together in a regular pattern B1 vibrate about fixed positions B1 liquid: close together but randomly arranged and able to move past each other B1 | 3 |
| (b) | energy used to break bonds between particles, not to increase kinetic energy the energy supplied is used to overcome forces between the particles / break bonds B1 so the kinetic energy (temperature) of the particles does not increase B1 | 2 |
| (c) | boiling at one temperature, throughout the liquid; evaporation at any temperature, surface only boiling occurs at a specific temperature, evaporation at any temperature B1 boiling happens throughout the liquid, evaporation only at the surface B1 | 2 |
| (d) | most energetic particles escape; average kinetic energy of remaining particles falls; lower temperature the most energetic molecules escape from the surface B1 the average kinetic energy of the remaining molecules decreases B1 so the temperature falls B1 | 3 |
Wet clothes are hung outside to dry.
State two conditions that make clothes dry quickly.
Explain why the clothes dry faster on a windy day.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | warm; windy; low humidity; spread out Any 2 of: warm temperature; windy; low humidity; large surface area (spread out) B2 | 2 |
| (b) | wind removes vapour, maintains gradient wind carries away the water vapour B1 so more molecules can escape from the surface B1 | 2 |
After swimming, a person standing in a breeze feels cold, even on a warm day.
Explain why.
State two factors that increase the rate of evaporation.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | evaporation cools the skin water evaporates from the skin B1 the most energetic molecules escape B1 the remaining water and skin are cooled B1 | 3 |
| (b) | higher temperature; larger surface area; air movement Any 2 of: higher temperature; larger surface area; moving air (wind) over the surface; lower humidity B2 | 2 |
Riyaz Shaikh has mentored IGCSE, IB and A Level students for 15+ years, one-on-one, online and in Mumbai. The hardest questions on this site are the ones he uses to find a student's weak points.
Meet Riyaz →Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in