I. Kinetic Molecular Theory

KMT

I. Kinetic Molecular Theory

KMT

Assumptions of KMTAssumptions of KMT

•All matter is composed of tiny particles

•These particles are in constant, random motion.

•Some particles are moving fast, some are moving slowly.

•Temperature is a measure of the average Kinetic Energy and is proportional to the average speed of the molecules.

KMT ModelKMT Model

http://preparatorychemistry.com/Bishop_KMT_frames.htm

Click on the link above to see how particles of matter behave according to the KMT.

Liquids & SolidsLiquids & SolidsLiquids & SolidsLiquids & Solids

II. Intermolecular ForcesII. Intermolecular Forces

Definition of IMFDefinition of IMF

Attractive forces between molecules.

Much weaker than chemical bonds within molecules.

a.k.a. van der Waals forces

Types of IMFTypes of IMF

London Dispersion Forces

View animation online.

Types of IMFTypes of IMF

Dipole-Dipole Forces

+ -

View animation online.

Types of IMFTypes of IMF

Hydrogen Bonding

Types of IMFTypes of IMF

III. Physical PropertiesIII. Physical Properties

Liquids & SolidsLiquids & SolidsLiquids & SolidsLiquids & Solids

Liquids vs. SolidsLiquids vs. Solids

LIQUIDS

Stronger than in gases

Y

high

N

slower than in gases

SOLIDS

Very strong

N

high

N

extremely slow

IMF Strength

Fluid

Density

Compressible

Diffusion

Liquid PropertiesLiquid Properties

Surface Tension• attractive force between particles in a

liquid that minimizes surface area

Liquid PropertiesLiquid Properties

Capillary Action• attractive force between the surface of

a liquid and the surface of a solid

water mercury

Types of SolidsTypes of Solids

Crystalline - repeating geometric pattern• covalent network• metallic• ionic• covalent molecular

Amorphous - no geometric pattern

decreasingm.p.

Types of SolidsTypes of Solids

Ionic(NaCl)

Metallic

Types of SolidsTypes of Solids

CovalentMolecular

(H2O)

CovalentNetwork

(SiO2 - quartz)

Amorphous(SiO2 - glass)

Liquids & SolidsLiquids & SolidsLiquids & SolidsLiquids & Solids

IV. Changes of StateIV. Changes of State

Phase ChangesPhase Changes

Most substances can exist in 3 states:• Solid• Liquid • Gas

Depends on temperature and pressure

Phase ChangesPhase Changes

Phase ChangesPhase Changes

Each state is referred to as a “Phase”• Ice water is a heterogeneous

mixture of 2 phasesWhen energy is added or removed,

one phase can change into another

Phase Changes Requiring Energy

Phase Changes Requiring Energy

MeltingVaporizationSublimation

MeltingMelting

Amount of energy needed to melt a substance depends on forces keeping particles together.• Melting water requires a high amount of energy

because of hydrogen bonding• Adding energy allows molecules to move

faster, breaking the hydrogen bonds• Melting point - Temperature at which the

forces holding crystal lattice together are broken and substance becomes liquid

Which has a higher m.p.?• polar or nonpolar?• covalent or ionic?

Phase ChangesPhase Changes

Melting Point• equal to freezing point

polar

ionic

IMF m.p.

VaporizationVaporization

In liquid water, some particles will have more kinetic energy than others.• When the particles have enough energy to

overcome the forces of attraction they will escape the liquid as a gas.

• Vapor - A substance that is liquid at room temperature and becomes gas.

• Vaporization - the process of changing a liquid to a gas

VaporizationVaporization

Evaporation - Vaporization that occurs at the surface of a liquid, molecules at the surface gain enough energy to overcome IMF

• Evaporation is gradual• Even at cold temperatures, some molecules have

enough energy to break the attractions and become gas.

Evaporation is how your body cools itself• Water in sweat absorbs heat from your body• Water evaporates leaving less heat in your body and a

lower ‘average kinetic energy’ (lower temperature)

Phase ChangesPhase Changes

Vapor PressureVapor Pressure• pressure of vapor above

a liquid at equilibrium

IMF v.p.temp v.p.

• depends on temp & IMF

p.478

temp

v.p

.

Phase ChangesPhase Changes

Boiling Point

IMF b.p.Patm b.p.

• Temperature at which the vapor pressure of a liquid equals the external atmospheric pressure

• depends on Patm & IMF

• Normal B.P. - b.p. at 1 atm

SublimationSublimation

Sublimation - when a substance goes from solid directly to gas without becoming a liquid• Solid iodine• Frozen carbon dioxide (dry ice)• Moth balls (p-dichlorobenzene)• Solid air fresheners• Ice cubes left in a freezer for a long time

Phase Changes the Release Energy

Phase Changes the Release Energy

CondensationDepositionFreezing

CondensationCondensation

Condensation – process of changing from gas to liquid• When molecule s lose energy,• Velocity of the molecules is reduced• Intermolecular forces take over• Hydrogen bonds form, energy is released (heat

comes out)• There are different causes for condensation,

however, all involve loss of energy:• Contact with cold item

Phase ChangesPhase Changes

EquilibriumEquilibrium• trapped molecules reach a balance

between evaporation & condensation

DepositionDeposition

Deposition – changing from gas directly to solid

• Snowflakes

FreezingFreezing

Freezing – process of changing from liquid to solid• Remove energy from liquid• Molecules don’t move past each other any

longer• Molecules stay in fixed, set position• Become solid

Phase ChangesPhase Changes

Energy Required Energy Released

Solid LiquidMelting or fusion

Liquid Solidfreezing

Liquid GasVaporization, evaporation or boiling

Gas Liquidcondensation

Solid Gassublimation

Gas Solidsolidification

Phase DiagramsPhase Diagrams

Phase diagram shows phase of matter at different temperatures and pressures• Each substance is unique• X-axis usually temperature• Y-axis usually pressure• There is usually a “Triple Point” where all

three phases can coexist• “Critical Point” – temperature and pressure

above which substance cannot exist as liquid

Phase Diagram - WaterPhase Diagram - Water

Phase Diagram CO2Phase Diagram CO2

Heating CurvesHeating Curves

Kinetic Energy Changes – Heat Energy speeds up the molecules.

Potential Energy Changes – Heat energy separates the molecules from solid to liquid, liquid to gas.

Heating CurvesHeating Curves

Temperature Change• change in KE (molecular motion) • depends on heat capacity

Heat Capacity• energy required to raise the temp of 1

gram of a substance by 1°C

Phase ChangePhase Change

The energy involved in a phase change is calculated using:

Heat of Fusion (Hfus)

Heat of Vaporization (Hvap)

Heat of FusionHeat of Fusion

Heat of Fusion is the energy required to change 1 gram of a substance from the solid to the liquid state without changing its temperature.

Heat of Fusion is used for calculations involving the phase changes of solid liquid or liquid solid

Heat of VaporizationHeat of Vaporization

Heat of Vaporization (Hvap)

• energy required to boil 1 gram of a substance at its b.p.

EX: sweating, steam burns, the drinking bird