states of matter. the kinetic-molecular theory describes the behavior of gases in terms of particles...
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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.
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
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.
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 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.