•A change of state is the conversion of a substance from one physical form to another

•All changes of state are physical changes

•Remember, in a physical change, the identity of a substance does not change

Energy and Changes of State

• During a change of state, During a change of state, the energy of a substance the energy of a substance changes.changes.

• The energy of a substance The energy of a substance is related to the motion of is related to the motion of its particlesits particles

• If energy is added to a If energy is added to a substance, its particles substance, its particles move faster. If energy is move faster. If energy is removed, its particles removed, its particles move slower.move slower.

Effect of temperature on the motion of solids,

liquids and gases

•The temperature of a substance is a The temperature of a substance is a measure of the speed of its particles and measure of the speed of its particles and therefore is a measure of its energy.therefore is a measure of its energy.

•For example, steam has a higher For example, steam has a higher temperature than liquid water, so temperature than liquid water, so particles in steam have more energy particles in steam have more energy than particles in liquid waterthan particles in liquid water

•A transfer of energy, known A transfer of energy, known as heat, causes the temperature as heat, causes the temperature of a substance to change, of a substance to change, which can lead to a which can lead to a change of state.change of state.

Melting: Solids to Liquids

• Melting is the change Melting is the change of state from a solid to of state from a solid to a liquida liquid

• The melting point of a The melting point of a substance is the substance is the temperature at which temperature at which the substance changes the substance changes from a solid to a liquidfrom a solid to a liquid

• Melting point is a Melting point is a characteristic property characteristic property of a substanceof a substance

Melting is endothermic

•For a solid to melt, particles must For a solid to melt, particles must overcome some of their overcome some of their attractions to each other.attractions to each other.

•When a solid is at its melting When a solid is at its melting point, any energy it absorbs point, any energy it absorbs increases the motion of its increases the motion of its molecules until they overcome molecules until they overcome their attractiontheir attraction

•Melting is an endothermic change Melting is an endothermic change because energy is absorbedbecause energy is absorbed

Freezing: Liquids to Solids

•Freezing is the Freezing is the change of state change of state from a liquid to a from a liquid to a solidsolid

•The temperature at The temperature at which a liquid which a liquid changes into a solid changes into a solid is its freezing point.is its freezing point.

•For a liquid to freeze, the motion For a liquid to freeze, the motion of its molecules must slow to the of its molecules must slow to the point where attractions between point where attractions between them overcome their motion.them overcome their motion.

• If a liquid is at its freezing point, If a liquid is at its freezing point, removing more energy causes removing more energy causes the particles to begin “locking” the particles to begin “locking” into place.into place.

•Freezing is an exothermic change Freezing is an exothermic change because energy is removed from, because energy is removed from, or taken out of, the substance as or taken out of, the substance as it changes state.it changes state.

Vaporization: :Liquids to Gases

•Vaporization is the Vaporization is the change of state from change of state from a liquid to a gas.a liquid to a gas.

•Boiling is Boiling is vaporization that vaporization that occurs throughout a occurs throughout a liquidliquid

•The temperature at The temperature at which a liquid boils is which a liquid boils is called its boiling called its boiling pointpoint

Pressure Affects Boiling Point

• Water boils at 100 degrees CelsiusWater boils at 100 degrees Celsius• In fact, water only boils at 100 degrees Celsius In fact, water only boils at 100 degrees Celsius

at sea level because of atmospheric pressure.at sea level because of atmospheric pressure.• Atmospheric pressure is caused by the weight Atmospheric pressure is caused by the weight

of the gases that make up the atmosphere.of the gases that make up the atmosphere.• The higher you go above sea level, the less air The higher you go above sea level, the less air

there is and the lower the atmospheric there is and the lower the atmospheric pressure.pressure.

• If you were to boil water at the top of a If you were to boil water at the top of a mountain, the boiling point would be lower mountain, the boiling point would be lower than 100 degrees Celsius.than 100 degrees Celsius.

•Evaporation is vaporization that Evaporation is vaporization that occurs at the surface of a liquid occurs at the surface of a liquid below its boiling point.below its boiling point.

•When you perspire, your body is When you perspire, your body is cooled through the process of cooled through the process of evaporation. evaporation.

•Sweat absorbs energy Sweat absorbs energy from your skin as it from your skin as it evaporatesevaporates

•You feel cooler because your You feel cooler because your body transfers energy to body transfers energy to the water.the water.

•In the water cycle, water is In the water cycle, water is transferred from the surface of transferred from the surface of the Earth to the atmosphere the Earth to the atmosphere through evaporationthrough evaporation

Condensation: Gases to Liquids

• Condensation is the change of state from a Condensation is the change of state from a gas to a liquid.gas to a liquid.

• The condensation point of a substance is the The condensation point of a substance is the temperature at which the gas becomes a temperature at which the gas becomes a liquid liquid

• For a gas to become a liquid, large numbers For a gas to become a liquid, large numbers of molecules must clump together.of molecules must clump together.

• Particles clump together when the attraction Particles clump together when the attraction between them overcomes their motion.between them overcomes their motion.

• For this to occur, energy must be removed For this to occur, energy must be removed from the gas to slow the particles down.from the gas to slow the particles down.

• Condensation is an exothermic change.Condensation is an exothermic change.

• The amount The amount of gaseous of gaseous

water that air can hold water that air can hold decreases as the decreases as the

temperature of the temperature of the air air decreases. decreases.

• As the air cools, some of the gaseous As the air cools, some of the gaseous water condenses to form small drops of water condenses to form small drops of liquid water.liquid water.

• These drops form clouds These drops form clouds in the sky and fog near in the sky and fog near the ground. the ground.

Sublimation: Solids Directly to Gases

• Sublimation is the change of state from Sublimation is the change of state from a solid directly into a gas.a solid directly into a gas.

• For a solid to change directly into a gas, For a solid to change directly into a gas, the molecules must move from being the molecules must move from being very tightly packed to being very spread very tightly packed to being very spread apart.apart.

• The attractions between the particles The attractions between the particles must be completely overcome.must be completely overcome.

• Because this requires the addition of Because this requires the addition of energy, sublimation is an endothermic energy, sublimation is an endothermic change.change.

Comparing Changes of State

•The state of a substance depends The state of a substance depends on how fast its molecules move and on how fast its molecules move and how strongly they are attracted to how strongly they are attracted to each othereach other

•A substance may undergo a A substance may undergo a physical change from one state to physical change from one state to another by an endothermic change another by an endothermic change (if energy is added) or an (if energy is added) or an exothermic change (if energy is exothermic change (if energy is removed)removed)

Change of State

Direction Endothermic

Exothermic

Examples

MeltingMelting Solid Solid liquidliquid

EndotherEndothermicmic

Ice melts in Ice melts in liquid waterliquid water

FreezingFreezing Liquid Liquid solidsolid

ExothermiExothermicc

Liquid water Liquid water freezes into freezes into iceice

VaporizatioVaporizationn

Liquid Liquid gasgas

EndotherEndothermicmic

Liquid water Liquid water vaporizes vaporizes into steaminto steam

CondensatiCondensationon

Gas Gas liquidliquid

ExothermiExothermicc

Steam Steam condenses condenses into liquid into liquid waterwater

SublimatioSublimationn

Solid Solid gas gas EndotherEndothermicmic

Solid dry ice Solid dry ice sublimes sublimes into gasinto gas

Temperature Changes Versus Change of State

• When substances lose or absorb energy, When substances lose or absorb energy, one of two things happens to the one of two things happens to the substancesubstance1. Its temperature changes1. Its temperature changes2. Its state changes2. Its state changes

• Remember, when the temperature of a Remember, when the temperature of a substance changes, the speed of the substance changes, the speed of the particles also changes.particles also changes.

• However, while a substance changes However, while a substance changes state, its temperature does not change state, its temperature does not change until the change of state is completeuntil the change of state is complete

Chapter ReviewSection 1

•The states of matter are the physical The states of matter are the physical forms in which a substance can exist.forms in which a substance can exist.

•The four states are solid, liquid, gas, The four states are solid, liquid, gas, and plasmaand plasma

•A solid has a definite shape and A solid has a definite shape and volumevolume

•A liquid has a definite volume but not A liquid has a definite volume but not a definite shapea definite shape

• A gas does not have a definite shape or A gas does not have a definite shape or volume.volume.

• A gas takes the shape and volume of its A gas takes the shape and volume of its container.container.

• Pressure is a force per unit areaPressure is a force per unit area• Boyle’s Law states that the volume of a Boyle’s Law states that the volume of a

gas increases as the pressure decreases if gas increases as the pressure decreases if the temperature does not changethe temperature does not change

• Charles’ Law states that the volume of a Charles’ Law states that the volume of a gas increases as the temperature gas increases as the temperature increases if the pressure does not changeincreases if the pressure does not change

• Plasma are composed of particles that Plasma are composed of particles that have broken aparthave broken apart

Chapter Review Section 2

•A change of state is the conversion A change of state is the conversion of a substance from one physical of a substance from one physical form to another.form to another.

•All changes of state are physical All changes of state are physical changeschanges

•Exothermic changes release energyExothermic changes release energy•Endothermic changes absorb Endothermic changes absorb

energyenergy

•Melting changes a solid to a liquidMelting changes a solid to a liquid•Freezing changes a liquid to a Freezing changes a liquid to a solidsolid

•Vaporization changes a liquid to a Vaporization changes a liquid to a gasgas

•There are two kinds of There are two kinds of vaporization: boiling and vaporization: boiling and evaporationevaporation

•Boiling occurs throughout a liquid Boiling occurs throughout a liquid at the boiling pointat the boiling point

•Evaporation occurs at the Evaporation occurs at the surface of a liquid, at a surface of a liquid, at a temperature below the boiling temperature below the boiling pointpoint

•Condensation changes a gas to Condensation changes a gas to a liquida liquid

•Sublimation changes a solid Sublimation changes a solid directly to a gasdirectly to a gas

•Temperature does not change Temperature does not change during a change of stateduring a change of state