Chp 3.3 - Phase ChangesChp 3.3 - Phase Changes
Pg. 84-91Pg. 84-91
Characteristics of Phase Changes
Characteristics of Phase Changes
When at least two states of a substance are present, each state is described as a phase
Phase change- a reversible physical change that occurs when a substance changes from one state of matter to another
Melting, freezing, vaporization, condensation, sublimation, and deposition are six common phase changes.
When at least two states of a substance are present, each state is described as a phase
Phase change- a reversible physical change that occurs when a substance changes from one state of matter to another
Melting, freezing, vaporization, condensation, sublimation, and deposition are six common phase changes.
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Temperature and Phase ChangesTemperature and Phase Changes The temperature of a
substance does not change during a phase change
Temperature remains the same until the phase change is complete
The temperature at which a substance freezes (freezing point) is identical to the temperature at which it melts (melting point)
The temperature of a substance does not change during a phase change
Temperature remains the same until the phase change is complete
The temperature at which a substance freezes (freezing point) is identical to the temperature at which it melts (melting point)
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Energy and Phase ChangesEnergy and Phase Changes
During a phase change energy is transferred between a substance and its surroundings
Energy is either absorbed or released during a phase change
Melting is an example of an endothermic change– Endothermic change - the
system absorbs energy
During a phase change energy is transferred between a substance and its surroundings
Energy is either absorbed or released during a phase change
Melting is an example of an endothermic change– Endothermic change - the
system absorbs energy
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Energy and Phase ChangesEnergy and Phase Changes The amount of energy
absorbed depends on the substance– One gram of water
absorbs 334 Joules of energy as it melts is its heat of fusion
The heat of fusion– Varies from substance to
substance– Heat of “melting”
Fusion is another term for melting
The amount of energy absorbed depends on the substance– One gram of water
absorbs 334 Joules of energy as it melts is its heat of fusion
The heat of fusion– Varies from substance to
substance– Heat of “melting”
Fusion is another term for melting
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Energy and Phase ChangesEnergy and Phase Changes
Freezing is an example of an exothermic change– Exothermic change - the
system releases energy to its surroundings
Freezing is an example of an exothermic change– Exothermic change - the
system releases energy to its surroundings
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MeltingMelting The arrangement of molecules in water becomes less
orderly as water melts and more orderly as water freezes
Melting– Attractions between molecules keep them in fixed positions– Heat flows from air to ice– Ice gains energy and molecules vibrate– Some gain enough energy to overcome the attractions and
move away– When all can move melting is complete
The arrangement of molecules in water becomes less orderly as water melts and more orderly as water freezes
Melting– Attractions between molecules keep them in fixed positions– Heat flows from air to ice– Ice gains energy and molecules vibrate– Some gain enough energy to overcome the attractions and
move away– When all can move melting is complete
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FreezingFreezing Freezing
– Energy flows from the water to the air in a freezer and the water cools down
– As kinetic energy of molecules decrease, the move more slowly
– Attractions between molecule take effect
– When all molecules have been drawn into orderly arrangement freezing is complete
Freezing– Energy flows from the water
to the air in a freezer and the water cools down
– As kinetic energy of molecules decrease, the move more slowly
– Attractions between molecule take effect
– When all molecules have been drawn into orderly arrangement freezing is complete
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Vaporization and CondensationVaporization and Condensation Vaporization - the phase change
in which a substance changes from a liquid to a gas
Vaporization is an endothermic process– A substance must absorb energy in
order to change from a liquid to a gas
One gram of water gains 2261 joules of energy when it vaporizes– This is its heat of vaporization– Heat of vaporization varies from
substance to substance
Vaporization - the phase change in which a substance changes from a liquid to a gas
Vaporization is an endothermic process– A substance must absorb energy in
order to change from a liquid to a gas
One gram of water gains 2261 joules of energy when it vaporizes– This is its heat of vaporization– Heat of vaporization varies from
substance to substance
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Vaporization Vaporization Evaporation takes place at the
surface of a liquid and occurs at temperatures below the boiling point
Evaporation - the process that changes a substance from a liquid to a gas at temperatures below the substance’s boiling point
Water in a closed container – Water evaporates and vapor collects
above the liquid– Vapor Pressure - caused by
collisions of the vapor and the walls of the container
– The vapor pressure increases as the temperature increases
Evaporation takes place at the surface of a liquid and occurs at temperatures below the boiling point
Evaporation - the process that changes a substance from a liquid to a gas at temperatures below the substance’s boiling point
Water in a closed container – Water evaporates and vapor collects
above the liquid– Vapor Pressure - caused by
collisions of the vapor and the walls of the container
– The vapor pressure increases as the temperature increases
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BoilingBoiling Heat a pot of water
– Temperature and vapor pressure increase When vapor pressure and atmospheric pressure become equal
the water boils As temperature increases water molecules move faster and
faster– When it reaches 100 degrees Celsius some molecules below the surface
overcome the attraction forces and form bubbles of water vapor– When the bubbles reach the surface they pop and release water vapor
into the air– Takes place throughout a liquid
Heat a pot of water– Temperature and vapor pressure increase
When vapor pressure and atmospheric pressure become equal the water boils
As temperature increases water molecules move faster and faster– When it reaches 100 degrees Celsius some molecules below the surface
overcome the attraction forces and form bubbles of water vapor– When the bubbles reach the surface they pop and release water vapor
into the air– Takes place throughout a liquid
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CondensationCondensation Condensation - the
phase change in which a substance changes from a gas or vapor to a liquid
An exothermic process Responsible for the
morning dew on grass and the “cloud” on the mirror after you take a shower.
Condensation - the phase change in which a substance changes from a gas or vapor to a liquid
An exothermic process Responsible for the
morning dew on grass and the “cloud” on the mirror after you take a shower.
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Sublimation and DepositionSublimation and Deposition Sublimation - phase change in
which a substance changes form a solid to a gas or vapor– Endothermic– Example is dry ice
Goes from solid carbon dioxide to a gas
The gas causes water vapor to condense and that’s how it forms clouds or the fog
Deposition - phase change in which a gas or vapor changes directly into a solid without first becoming a liquid– Exothermic– Opposite of sublimation– Causes frost on cold window
glass
Sublimation - phase change in which a substance changes form a solid to a gas or vapor– Endothermic– Example is dry ice
Goes from solid carbon dioxide to a gas
The gas causes water vapor to condense and that’s how it forms clouds or the fog
Deposition - phase change in which a gas or vapor changes directly into a solid without first becoming a liquid– Exothermic– Opposite of sublimation– Causes frost on cold window
glass
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The EndThe End
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