Latent HeatLatent Heat

Phases of MatterPhases of Matter

SolidSolid GasGas LiquidLiquid

The properties of solids, liquids, and gases differ.The properties of solids, liquids, and gases differ. How does matter change state?How does matter change state?

Watched PotWatched Pot

You want to cook a pot of potatoes in boiling water. You want to cook a pot of potatoes in boiling water. To use energy most efficiently, you shouldTo use energy most efficiently, you should

• A) Heat it up quickly and leave it at a full boilA) Heat it up quickly and leave it at a full boil• B) Heat it up slowly and turn it up to a full boilB) Heat it up slowly and turn it up to a full boil• C) Heat it up quickly and turn it down to simmerC) Heat it up quickly and turn it down to simmer• D) Heat it up slowly and leave it at a low boilD) Heat it up slowly and leave it at a low boil

Energy of PhaseEnergy of Phase

Internal energy can be Internal energy can be stored as bonds between stored as bonds between atoms and molecules.atoms and molecules.

• Solids have the strongest Solids have the strongest bondsbonds

• Energy required to break Energy required to break them to a liquidthem to a liquid

Heat of TransformationHeat of Transformation

As a system reaches the As a system reaches the point of a phase change heat point of a phase change heat no longer changes the no longer changes the temperature.temperature.

The heat is used to change The heat is used to change the phase.the phase.

heat of fusion heat of vaporization

Latent HeatLatent Heat

The heat of transformation The heat of transformation per unit mass is called the per unit mass is called the latent heat latent heat (L).(L).• Measured in J/kgMeasured in J/kg

It takes as much energy to It takes as much energy to melt 1 g of ice as it does to melt 1 g of ice as it does to raise the temperature from raise the temperature from 0 0 C to 80 C to 80 C.C.

Material (f or v)Material (f or v) Latent HeatLatent Heat

Mercury (f)Mercury (f) 11.3 kJ/kg11.3 kJ/kg

Lead (f)Lead (f) 24.7 kJ/kg24.7 kJ/kg

Uranium (f)Uranium (f) 82.8 kJ/kg82.8 kJ/kg

Copper (f)Copper (f) 205 kJ/kg 205 kJ/kg

Water (f)Water (f) 334 kJ/kg334 kJ/kg

Oxygen (v)Oxygen (v)213 kJ/kg213 kJ/kg

Water (v)Water (v) 2300 kJ/kg 2300 kJ/kg

LmQ

Phase DiagramsPhase Diagrams

For each temperature and For each temperature and pressure a material is in a pressure a material is in a specific state.specific state.

The The triple pointtriple point is uniquely is uniquely defined for each material.defined for each material.• PP33 for water is used to for water is used to

define the Kelvindefine the Kelvin

The The critical pointcritical point is where is where there is no difference there is no difference between liquid and gas.between liquid and gas.

Phase diagram for water

SublimationSublimation

At low pressures a solid can At low pressures a solid can go directly to a gas and vice go directly to a gas and vice versa.versa.

This process is called This process is called sublimationsublimation..

• Dry ice to gaseous carbon Dry ice to gaseous carbon dioxidedioxide

• Water vapor to frostWater vapor to frost

There is a latent heat of There is a latent heat of sublimationsublimation

Phase diagram for carbon dioxide

Summer CoolerSummer Cooler

200 g of ice at -10 200 g of ice at -10 C is C is added to 1.0 kg of water at added to 1.0 kg of water at 15 15 C.C.

Is there enough ice to cool Is there enough ice to cool the water to 0 the water to 0 C?C?

Find the amount of heat Find the amount of heat needed to bring the ice to 0 needed to bring the ice to 0 C and melt it.C and melt it.• QQii = = mcmcTT + + mLmLff

• QQii = 70.9 kJ = 70.9 kJ

Find the heat needed to cool Find the heat needed to cool the water down to 0 the water down to 0 C.C.• QQww = = mcmcTT

• QQww = 62.8 kJ = 62.8 kJ

Yes, there’s enough ice.Yes, there’s enough ice.next