The energy involved in change of state
2 marks · EasyA scientist records the temperature of a pure substance as it is heated steadily. The measured values are shown in the table below.
| Time (min) | Temperature (°C) |
|---|---|
| 0 | 20 |
| 2 | 40 |
| 4 | 60 |
| 6 | 80 |
| 8 | 80 |
| 10 | 100 |
Explain what the constant temperature at 80 °C from 6 to 8 minutes shows about what is happening to the substance.
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.
Show answer
The substance is melting; the temperature stays at 80 °C while changing state.
Also accept: It is changing from solid to liquid; the temperature stays constant during melting.
Common mistakes: Thinks heating stopped or thermometer was broken.
Show mark scheme and worked solution
Marking points
B1 · 1 mark · Identifies that change of state is occurring (melting).
B2 · 1 mark · Explains temperature stays constant while change of state takes place.
Worked solution
Between 6 and 8 minutes, the substance is melting. The temperature remains constant at 80 °C until all of the substance has changed from solid to liquid.