Interconversions between the three states of matter
2 marks · EasyWhen a solid substance is heated from 10 °C to 70 °C, it melts completely at 50 °C. Use particle theory to calculate the number of changes of state that take place as the temperature increases from 10 °C to 70 °C.
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1 (±0)
Also accept: one
Common mistakes: Saying 2, counting 'solid to liquid' and 'heating' as separate changes
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Marking points
M1 · 1 mark · Identifies the temperature at which the change of state occurs (50 °C).
A1 · 1 mark · Correctly calculates there is 1 change of state (solid to liquid) between 10 °C and 70 °C.
Worked solution
The substance is a solid at 10 °C. At 50 °C it melts, so between 10 °C and 50 °C it is a solid, and above 50 °C it is a liquid.
There is only one change of state (melting) as the substance changes from solid to liquid at 50 °C.