The energy involved in change of state
3 marks · NormalA mixture of ice and water is kept at 0°C. Explain, using ideas about energy and particles, what happens to the temperature when more ice melts.
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The temperature does not increase as more ice melts. The energy supplied is used to break the forces holding the ice particles together, changing them into water particles at 0°C. Only when all the ice has melted will further heating increase the temperature. While both ice and water are present at 0°C, the temperature stays at 0°C.
Common mistakes: Saying temperature increases as ice melts; Omitting energy is used to break bonds
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Marking points
B1 · 1 mark · States temperature does not rise while ice is melting
M1 · 1 mark · Explains energy is used for breaking forces (or bonds) between ice particles
B2 · 1 mark · Mentions that further heating increases temperature only after all ice has melted
Worked solution
As ice melts in water at 0°C, the temperature remains at 0°C. Any energy supplied is used to break the forces between solid ice particles, turning them into liquid water at 0°C. When all the ice has melted, then heating will increase the temperature of the water.