Solid, Liquid, Gas

(a) Particles in solid (b) Particles in liquid (c) Particles in gas

Solid

H2O(s) Ice

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

Ice

H2O(s) Ice

Photograph of ice model Photograph of snowflakes

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Liquid

H2O(l) Water

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

In a liquid• molecules are in constant motion

• there are appreciable intermolecular forces

• molecules are close together

• Liquids are almost incompressible

• Liquids do not fill the container

Gas

H2O(g) Steam

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

Liquids

The two key properties we need to describe areEVAPORATIONEVAPORATION and its opposite CONDENSATIONCONDENSATION

add energy and break intermolecular bonds

EVAPORATION

release energy and form intermolecular bonds

CONDENSATION

States of Matter

Gas, Liquid, and Solid

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 441

Gas Liquid Solid

States of Matter

Solid Liquid Gas

Holds Shape

Fixed Volume

Shape of Container

Free Surface

Fixed Volume

Shape of Container

Volume of Container

heat heat

Some Properties of Solids, Liquids, and Gases

Property Solid Liquid Gas

Shape Has definite shape Takes the shape of Takes the shape the container of its container

Volume Has a definite volume Has a definite volume Fills the volume of the container

Arrangement of Fixed, very close Random, close Random, far apartParticles

Interactions between Very strong Strong Essentially noneparticles

• To evaporate, molecules must have sufficient energy to break IM forces.

• Molecules at the surface break away and become gas.

• Only those with enough KE escape.• Breaking IM forces requires energy. The

process of evaporation is endothermicendothermic.• Evaporation is a cooling process.• It requires heat.

Evaporation

Change from gas to liquid

Achieves a dynamic equilibrium with vaporization in a closed system.

What is a closed system?

A closed system means matter can’t go in or out. (put a cork in it)

What the heck is a “dynamic equilibrium?”

Condensation

When first sealed, the molecules gradually escape the surface of the liquid.

As the molecules build up above the liquid - some condense back to a liquid.

The rate at which the molecules evaporate and condense are equal.

Dynamic Equilibrium

As time goes by the rate of vaporization remains constant but the rate of condensation increases because there are more molecules to condense.

Equilibrium is reached when:Rate of Vaporization = Rate of Condensation

Molecules are constantly changing phase “dynamic”

The total amount of liquid and vapor remains constant “equilibrium”

Dynamic Equilibrium

• Vaporization is an endothermic process - it requires heat.

• Energy is required to overcome intermolecular forces

• Responsible for cool earth• Why we sweat

Vaporization

Energy Changes Accompanying Phase Changes

Solid

Liquid

Gas

Melting Freezing

Deposition

CondensationVaporization

Sublimation

Ene

rgy

of s

yste

m

Brown, LeMay, Bursten, Chemistry 2000, page 405