States of Matter

The Kinetic-Molecular Theory

Describes the behavior of gases in terms of particles in motion.

Gases are composed of small particles separated from one another by empty space. This spacing means no significant IMF exist among particles.

Gas particles are in constant, random motion.

Temperature is a measure of the average kinetic energy of particles in matter.

http://comp.uark.edu/~jgeabana/mol_dyn/KinThI.html

http://www.chm.davidson.edu/ChemistryApplets/KineticMolecularTheory/BasicConcepts.html

Particles collidewith one anotherand the sides of the container.Energy can betransferred uponcollision, but thenet result is energyis conserved =elastic collisions.

Properties of Gases

Low density:A great deal of space exists between gasparticles. Since density is a measure of

m/V, for a given mass of a gas, the density will be thousands of times lower than a comparable mass of a solid.

Compression and expansion:The large amount of space that existsbetween gas particles allows them tobe easily pushed into a smaller volume.

Diffusion and effusion:The random motion of gas particlescauses gases to mix until they are evenly distributed. This process iscalled diffusion and depends on the mass of the particles involved. The lighter the particle, the faster it moves.

Effusion is the escape of a gas through a tiny opening.

Experiments to measure the rates of effusion of different gases indicated an inverse relationship between the rate of effusion and the mass of the gas.

In other words, the lighter the gas, the faster the particles will move.

r1 = molar mass2

r2 molar mass1

Calculate the ratio of the effusion rates for nitrogen gas and neon.

Calculate the molar mass of butane. Butane’s rate of diffusion is 3.8 timesslower than that of helium.

Gas Pressure

Force per unit area.Gas particles exert pressure when they

collide with the sides of their container.Atmospheric pressure is the force exerted

by the particles surrounding the earth.Air pressure varies with your position on

earth. At the top of a mountain, the atmospheric pressure is less than that at sea level since the column of air pressing down on you is less.

Measuring Pressure

A barometer measures atmospheric pressure.The height of the mercury in the column is

generally 760 mm.The forces exerted on the column of mercury

are the force of gravity downward and the upward force due to the air.

A manometer is a device used to measure gas pressure in a closed container.

Units of Pressure

SI unit is the pascal (Pa).1 Pa = 1 N/m2

Common units of pressure are the psi (pounds per square inch) used to measure tire pressure and the atmosphere (atm)

1 atm = 760 mm Hg = 101.325 kPa

Perform the following conversions:

3.5 atm to mm Hg.

450 mm Hg to kPa.

99.5 kPa to atm.

Dalton’s Law of Partial Pressures

Examine the flask to the left.

What gas particles are present in the flask?

Dalton’s law states that the total pressure of the gas in the mixture is the sum of all the pressures.

Gases “collected over water”

The best application of Dalton’s law to labsituations is when a gas is collected by bubbling the gas into a bottle containing water.

The pressure inside the flask is the sum of thepressures of the collected gas and water vapor.

Pdry gas = Patm – Pwater vapor P of the water vapor is T dependent.

Forces of Attraction

The state of a substance depends on the forces of attraction within and between its particles.

Intramolecular attractive forces are the ionic, covalent or metallic bonds within the substance.

Intermolecular attractive forces exist between particles of the same or different substances.

London Dispersion Forces

Dispersion forces are weak forces caused by temporary shifts in the density of electrons surrounding the nucleus. The strength of dispersion forces is directly related to the number of electrons that a substance has.

Weakest of the three IMF and are significant primarily in large nonpolar molecules.

Dipole-Dipole Forces

Attractive forces between oppositely charged regions of polar molecules.

Stronger than dispersion forces but molecules must have comparable mass.

Hydrogen Bonding

Strongest of the 3 IMF

Occurs when hydrogen is bonded to a small, highly electronegative atom.

Exists when H is bonded to F, O or N.

The properties of water, a molecule essentialfor sustaining life are due to hydrogen bonding.

The low density of ice as compared to liquidwater, the existence of water as a liquid atroom temperature, the surface tension of water,and the high specific heat of water are allproperties directly related to hydrogen bonding.

http://www.harcourtschool.com/activity/states_of_matter

Liquids

KM theory appliesto liquids when IMFare considered.

Liquids assume theshape of their container and flow.

Properties of Liquids

Density and compression:Liquids are more dense than theirvapor. Higher density due to theIMF holding the particles together.

Liquids can be compressed slightlybut a great deal of pressure must beapplied.

FluidityGases and liquids are able to

flow.Liquids can diffuse through

eachother, but at a rate more slowly than gases.

ViscosityA measure of the resistance of a liquid to flow.

Surface TensionDefined as the energy required toincrease the surface area of a liquid by a given amount.

Capillary ActionAdhesive and cohesive forcesaccount for the behavior of liquids in small tubes calledcapillary tubes.

Forces of attractionbetween the waterand the glass are greater than the forces between water molecules, sothe water risesalong the glass.

Solids

Strong attractive forcesexist between solidparticles.More order exists insolids than liquids; as a result,

solidsdo not flow.

Properties of Solids

DensitySince particles are more

closely packed, the density of solids is greater than those of liquids.

CrystallinityParticles of a solid are

arranged in a particular way.

Types of Unit Cells

Simple Cubic

Body-centered Cubic

Face-centered Cubic

Types of Crystalline Solids

Molecular solids: held together by dispersion forces; fairly soft, low melting points.

Covalent Network solids: very hard solids with high melting points.

Ionic solids: positive and negative ions held together by electrostatic forces of attraction; hard, brittle, high melting points.

Types of Crystalline Solids

Metallic solids: held together by metallic bonds; electrons are free to move around nuclei; soft to very hard; low to very high melting point; excellent thermal and electrical conductors; malleable and ductile.

List the names for the following phase transitions:

solid liquid

liquid gas

solid gas

liquid solid

gas liquid

gas solid

Endothermic Phase Changes

Endothermic phase changes require the input of energy.

Melting: solid liquid.Vaporizing: liquid gas.Subliming: solid gas.

Melting point: temperature at which theforces holding the crystal together arebroken and it becomes a liquid.

Evaporation: vaporization occurring only at the surface of a liquid.

Vapor Pressure

Pressure exerted by a vapor over a liquid.

The temperature at which the vapor pressure of the liquid equals atmospheric pressure is called the boiling point.

Exothermic Phase Changes

Exothermic phase changes release energy.Condensation: gas liquid.Deposition: gas solid.Freezing: liquid solid.

http://jersey.uoregon.edu/vlab/Piston/index.html

http://www.chm.davidson.edu/ChemistryApplets/KineticMolecularTheory/PT.html