States of Matter and

Intermolecular ForcesChapter 11

11-1 States and State Changes

Solids• Particles have an orderly,

fixed arrangement• Fixed volumes and shapes

Liquids• Particles move easily

past one another (have more energy)• Fixed volume, no fixed

shape

Viscosity• Ability to Flow• Honey is very viscous

Surface Wetting

Adhesion

• Stick to something else

Cohesion

• Stick to each other

Capillary Action• The movement of

water up through a tube – because of adhesion and cohesion

Surface Tension• Cohesive forces• Causes liquids to minimize surface

area• That’s why water drops are round

Gas• Particles are

independent• Far apart• No fixed volume or

shape• Gases and liquids are

fluids

Changing State

• Freezing – liquid becomes a solid• Melting – solid becomes a liquid• Evaporation – liquid becomes gas• Condensation – gas becomes liquid• Sublimation – solid becomes gas• Deposition – gas becomes solid

Temperature, Energy, and State

Evaporation• High energy particles change to gas• Causes the substance to cool

Boiling Point

• The temperature at which bubbles of vapor rise to the surface• Also depends on atmospheric

pressure

Intermolecular Forces11-2

Attraction between Particles• Takes energy to separate particles (change state)• The stronger the force, the more energy it takes

• The boiling and melting point is a good measure of the strength of the force

• Strong force of attraction = high boiling point

Force of attraction in Ions• Higher force of attraction then between molecules• High melting points

• Smaller ions larger force (NaCl > KCl)• Larger charge larger force (CaF2 > NaCl)

Intermolecular Forces• The Force of Attraction between molecules

Types of Intermolecular Forces

• Dipole-Dipole Forces• Hydrogen Bonds• London Dispersion Forces• All are short range• Little effect on gases• Many gases have low

boiling point (that is why they are gases)

Polar Molecule

• A molecule that has an unequal distribution of charge• One end slightly positive, One end slightly negative• Caused by difference in electronegativity of the atoms

Dipole-Dipole Forces• Interaction between polar molecules• Positive end of one molecule attracts the negative end of another

Dipole-Dipole Forces and Boiling Point• The more polar the molecules, the stronger the force

between them, the higher the boiling point

Hydrogen Bonds• When a hydrogen atom of one molecule is attracted to an atom of a different

molecule• Water

Hydrogen Bonds• Can create a larger

difference in electronegativity• Also hydrogen is small

and has only 1 electron • Which increases the

bond strength• Which increases the

boiling point

Hydrogen Bonds and Water• Water has unique

properties, because of hydrogen bonds• Can form multiple

hydrogen bonds Strong intermolecular forces

Solid water is less dense than liquid water

• Ice Floats• Ponds freeze

from top down• Expanding ice

cracks rocks and concrete

London Dispersion Forces

• The force that hold non-polar molecules together• The weakest of the

intermolecular forces• Explains why some non-

polar molecules are not gases

London Dispersion Forces• Nonpolar molecules can become temporary dipoles (electrons move from side

to side)• Causes molecules to attract each other

London Dispersion Forces• Nearby molecules always attract• The more

electrons, the stronger the force

Energy of State Changes

11-3

Enthalpy• The total energy of a system

Entropy

• A measure of system’s disorder

Enthalpy of Fusion• The energy added during melting or removed during

freezing• AKA the heat of fusion

Entropy of Fusion• The increase of entropy when a solid melts

Enthalpy of Vaporization• The energy added during evaporation

Entropy of Vaporization• The increase of entropy when a liquid evaporates• Much larger than entropy of fusion

The molar enthalpy of fusion• The heat energy needed

to melt 1 mol of a substance

For water it is 6.01 kJ/mol

The molar enthalpy of vaporization

• The heat energy needed to evaporate 1 mol of a substance

For water it is 40.67 kJ/mol

Phase Equilibrium11-4

System• A set of components that are being studied

Phase• A region that has the same

composition and properties throughout

Lava lamp – Two phases of liquid- Different chemical compositions

Phase

• Water – Two phases, same chemical composition - Different States

Dynamic Equilibrium

• The net amount of substance in a given phase stays the same• Eg. The rate of evaporation

equals the rate of condensation

Which of these?

Vapor Pressure• The pressure exerted by a gas in equilibrium with a liquid

• Boiling point – The temp at which vapor pressure equals the external pressure

As temperature increases, vapor pressure increases

• Normal Boiling Point – when vapor pressure equals the atmospheric pressure

Phase Diagrams• A graph of the

relationship between the state of a substance and its temperature and pressure

Phase Diagrams

• 3 lines• Vapor pressure for

liquid-gas equilibrium A-B• Liquid-solid

equilibrium A-D• Solid gas equilibrium

A-C

Triple Point

• The temperature and pressure at which all three states are in equilibrium

Critical Point• The temperature and pressure at which the gas and liquid states become

identical

• Called a supercritical fluid

Supercritical Fluid