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Melting point: It is the fixed temperature at which a solid changes into a liquid.
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Freezing point: It is the fixed temperature at which a liquid changes into a solid.
Note: Melting point and freezing point are the same temperature. For water it is 0oC.
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Boiling point: It is the fixed temperature at which a liquid changes into a gas.
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Condensation point: It is the fixed temperature at which a gas changes into a liquid.
Note: Boiling point and condensation point are the same temperature. For water it is 100oC.
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Changes of state
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Melting: It is the change of state from solid to liquid without a change in temperature.
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Solidification / Freezing: It is the change of state from liquid to solid without a change in temperature.
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Boiling: It is the change of state from liquid to gas without a change in temperature.
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Condensation: It is the change of state from gas to liquid without a change in temperature.
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Evaporation: It is the change of state from liquid to gas at any temperature.
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Factors that affect melting and boiling points are:
Action
Freezing / melting point
Boiling point
Add impurity
Decreases
Increases
Add pressure
Decreases
Increases
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Latent heat means hidden heat. It is because as long as a change of state is going on, the heat supplied or taken does not produce a change in temperature.
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Latent heat of fusion: It is the heat energy required to change a solid to liquid or vice versa without any change in temperature.
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Unit: J
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Specific latent heat of fusion: It is the heat energy required to change 1 kg of a solid to liquid or vice versa without a change in temperature.
l = E / m
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Unit: J/kg
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Latent heat of vaporisation: It is the heat energy required to change a liquid to vapour or vice versa without any change in temperature.
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Unit: J
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Specific latent heat of vaporisation: It is the heat energy required to change 1 kg of a liquid to gas or vice versa without any change in temperature.
l = E / m
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Unit: J/kg
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Comparison between boiling and evaporation
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Unlike boiling, evaporation happens at any temperature.
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Unlike boiling, evaporation only happens at the surface.
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Unlike boiling, evaporation is a slow process.
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Unlike boiling, evaporation does not cause bubbling.
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Unlike boiling, evaporation may not require a special heat source. The heat required for evaporation can come from the surroundings.
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Evaporation causes a decrease in temperature because higher energy molecules escape from the surface and the average kinetic energy of the molecules left in the liquid comes down.
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A refrigerator uses evaporation and condensation to work.
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Freon condenses (when compressed) to release heat and evaporates when (decompressed) to absorb heat.
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Factors that increase the rate of evaporation are:
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higher temperature
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less humidity (which refers to the amount of moisture in the air)
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more surface area
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movement of air
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lower atmospheric pressure
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using another liquid with a lower boiling point
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