Freezing/Melting Point
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The temperature at which something changes from a liquid to a solid or a solid to
a liquid.
The freezing/melting point is a constant value for a given substance. Each
substance has its own unique freezing/melting point.
All matter has a freezing/melting point, but the value is different for different
substances
The freezing/melting point for water is 0˚ C. At 0˚ C or colder, water will be a
solid, but if the temperature is above 0˚ C, water will be a liquid.
Increase = to go up
Decrease = to go down
Changing from a liquid to a solid or a solid to a liquid is an example of a physical
property.
Questions
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What happens when a substance reaches its freezing point?
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When a solid turns into a liquid, what constant value has it reached?
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What is the freezing/melting point of water?
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If the temperature outside is 2˚C, would the temperature have to increase or
decrease to turn liquid water into ice?
Revised August 2008
Boiling Point
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The boiling point is the temperature at which a liquid turns into a gas.
This value is a constant.
As a substance reaches its boiling point the molecules move faster and faster.
Changing from a liquid to a gas is an example of a physical change.
The steam that rises from a pot of boiling water is water vapor (gas).
The boiling point of water is 100˚C.
Questions:
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Explain what happens when a liquid reaches its boiling point.
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What is the boiling point of water?
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List some examples you see in your everyday life of substances that reach their
boiling points.
Revised August 2008