Chp 3.3 - Phase Changes Pg. 84-91. Characteristics of Phase Changes When at least two states of a substance are present, each state is described as.

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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