Change of State
6 marks · NormalA student heats a beaker of ice at -10 °C. The temperature is measured every minute and the following readings are recorded:
| Time (min) | Temperature (°C) |
|---|---|
| 0 | -10 |
| 2 | -5 |
| 4 | 0 |
| 8 | 0 |
| 10 | 10 |
Describe the changes in the state of the substance over the 10 minutes.
Explain why the temperature remains at 0 °C from 4 to 8 minutes, even though energy is still being supplied.
Using the particle model, describe what happens to the arrangement and movement of particles during this period.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) The ice first warms up as a solid. At 0 °C, it starts to melt. Between 4 and 8 minutes, the ice is melting into water at a constant temperature. After 8 minutes, all ice has melted and the water warms up. · must show Solid warming, Melting at constant temperature, Liquid warms after melting
(b) The temperature remains at 0 °C while the ice is melting because all energy supplied is used to break bonds between particles, not to increase temperature. · must show Energy used to break bonds/forces, No rise in temperature during melting
(c) Particles become less ordered and start to move more freely as the solid becomes liquid. · must show Arrangement changes from fixed to more random, Particles move more freely
Common mistakes: Omitting mention of melting; Confusing freezing with melting
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States ice warms up as a solid until 0 °C.
B2 (a) · 1 mark · Mentions melting at constant temperature between 4 and 8 minutes.
B3 (a) · 1 mark · Mentions water warms after all ice has melted (after 8 minutes).
B4 (b) · 1 mark · Explains energy is used to break forces/bonds between particles.
B5 (b) · 1 mark · States no temperature increase during melting phase.
B6 (c) · 1 mark · Describes arrangement becomes less regular and movement of particles increases.
Worked solution
(a) From 0 to 4 min: Solid ice warms from -10 °C to 0 °C. From 4 to 8 min: Temperature stays at 0 °C while the ice melts to form liquid water. After 8 min: All ice has melted, and the temperature of the water rises above 0 °C.
(b) The temperature remains constant during melting because the energy input is used to break the bonds between particles (latent heat), rather than increasing their kinetic energy.
(c) During melting, the particles move out of their fixed positions and begin to move more freely as the substance becomes liquid.