Phases of Matter andPhases of Matter andPhase ChangesPhase Changes

Unit 7Unit 7

Chapter 13Chapter 13

Phases of MatterPhases of MatterLiquids and SolidsLiquids and Solids

Molecular Level Comparison of Gases, Molecular Level Comparison of Gases, Liquids and Solids.Liquids and Solids.

•Molecular Motion -Kinetic-molecular theory predicts the constant motion of the liquid particles

•Individual liquid molecules do not have fixed positions in the liquid.

•Volume - Forces of attraction between liquid particles limit their range of motion so that the particles remain closely packed in a fixed volume.

Liquid Properties

•Shape - Liquids can take the shape of their container

Properties of LiquidsProperties of Liquids DensityDensity - Like gases, liquids can be - Like gases, liquids can be

compressed. But the change in volume for compressed. But the change in volume for liquids is much liquids is much smallersmaller because liquid particles because liquid particles are already are already tightly packedtightly packed together. together.

•Diffusion - A liquid diffuses (mix) more slowly than a gas at the same temperature, however, because intermolecular attractions interfere with the flow.

Properties of SolidsProperties of Solids•Exist in ordered patterns Most solids have a crystalline shape repeated over and over Exception: Glass (considered an amorphous solid, which means that the molecules are in stuck in random positions

•Diffusion - Cannot diffuse (cannot mix spontaneously with other solids)

•Molecular Motion - Particles are in fixed positions so they just vibrate in place.

More Solid PropertiesMore Solid Properties

Solids are usually the Solids are usually the most most dense of the dense of the three statesthree states Exception: Exception: WaterWater

•Cannot be compressed – therefore they have fixed volumes.

•Density - The particles in a solid are more closely packed than those in a liquid.

Changes In StateChanges In State

Solid

Liquid Gas

Freezing

Melting

SublimationDeposition

Vaporization

Condensation

Exothermic vs. EndothermicExothermic vs. Endothermic Exothermic ChangeExothermic Change – Heat Energy is – Heat Energy is releasedreleased to to

the surroundings.the surroundings. Molecules Molecules slowslow down, extra energy is down, extra energy is

transferred to surrounding.transferred to surrounding. CoolingCooling phase changes are exothermic phase changes are exothermic

•Endothermic Change – Heat energy is absorbed by the system

-Molecules move faster as they absorb energy

-Phase changes that require energy (or heat) are endothermic

Heating & Cooling CurveHeating & Cooling CurveFor a Pure SubstanceFor a Pure Substance

Energy Added

Tem

pera

ture

o C

Solid heating

Melting

Solid & Liquid

Liquid heats

Gas heats

Vaporization

Liquid and gas

Boiling/condensation Temperature

Melting/Freezing Temperature

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