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States of Matter
Common States of MatterGases
What do you know about gases?Liquids
What do you know about liquids?Solids
What do you know about solids?States of matter phet
Kinetic Molecular TheoryThe KMT relates the kinetic energy of molecules to states of matter.
Intro to KMT
The Nature of Gases:Kinetic Molecular Theory (KMT)• Kinetic Energy: what is it?• Energy of a moving object: Ek = ½ mv2
• Assumptions of KMT as it applies to gases• Gas particles…1. Have insignificant volume, (≈ 0)
2. Are in constant, random motion3. Collisions are perfectly elastic4. Do not attract or repel one another5. Average Ek is proportional to absolute
temp
Movement of Gas Particles in a Container
Gas Pressure• Pressure = Force/Area:
• P = F/A• Gas pressure is the result of collision of gas
particles with an object. • Why is there no pressure in a vacuum?• It is the sum of the force of collisions per
unit area
Atmospheric PressureAtmospheric pressure is due to the force of atmospheric gases colliding with objects and weight of atmospheric gases.
BarometerMeasures
atmospheric pressure
Invented by Alejandro Torricelli
Patm presses down on the surface, forces Hg up into the tube
Units of PressurePascal (SI unit) PaMillimeters of Hg mmHgAtmosphere atmTorr torrConversion factors @ 25C: Know these!
1 atm = 760 mmHg = 760 torr = 101.3 kPa = 14.7 psi
Converting Between Units of PressureConvert a pressure of 385 mmHg to
kilopascals (kPa)How would you do it?51.3 kPa
Kinetic Energy & Temperature
13.2 The Nature of Liquids
Both liquids and gases are fluids, i.e. they can flow
13.2 The Nature of LiquidsKey difference from gases:Molecules are close enough to have
intermolecular forces of attractionThis is why liquids have a definite volumeBut not close enough to fix them in placeThis is why molecules of liquids can move
past one another (flow)Condensed matter:
Liquids and solids are known as condensed phases of matter
Evaporation
EvaporationVaporization: the conversion of a liquid to a gas or
vaporEvaporation: vaporization occurring at the surface
of a liquidDuring evaporation, molecules of liquid with sufficient
KE “escape” in to the vapor phaseIn a closed container, some molecules that escaped
re-enter into the liquid phase (condense)Eventually and equilibrium is reached where…The rate of evaporation equals the rate of
condensationWhat would happen to the rate of evaporation when a
liquid is heated? Why?
Vapor PressureVapor pressure is a measure of the force exerted by a gas above a liquid.
13.2
States of matter phet
Vapor PressureIn a closed container, as molecules escape
into the vapor phase, pressure buildsThis is vapor pressureAt a certain pressure, the rate of
vaporization equals the rate of condensationThis is an example of “dynamic equilibrium”
Then vapor pressure is constant
Vapor PressureDepends upon the liquidDepends upon temperature
Vapor PressureDepends upon the liquidDepends upon temperature
Boiling PointA liquid boils when the particles
thoughout the liquid have enough KE to vaporize
This occurs when the vapor pressure of the liquid equals the external pressure on the liquid (e.g. atmospheric pressure)
This means that a liquid can boil at different temperatures, depending on the external pressure.
Boiling Point & Normal Boiling Point Normal boiling
point is the boiling temperature when atmospheric pressure (Patm) = 1 atm
What is the normal BP for ethanol?
What is the BP for ethanol at Patm = 600 torr?
13.3 SolidsCrystal Structure
Simple cubicBody centered
cubicFace centered
cubicAllotropesAmorphous solidsGlasses
Some Types of Unit Cells
AllotropesAllotropes are varying forms of an elementExample: oxygen (O2) and ozone (O3)Example: allotropes of carbon
Non-Crystalline SolidsAmorphous solids lack an ordered internal
structure.Examples: rubber, plastic, asphalt, glass
13.4 Changes of StateVaporization/Condensation
Liquid ↔ GasEvaporationBoilingVapor vs. Gas
Melting/FreezingLiquid ↔ SolidSolidification
Sublimation/DepositionSolid ↔ Vapor I2 (s) → I2 (g)
SublimationSolid VaporSublimation occurs
in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.
Depositiono Vapor Solid
Phase DiagramsShow pressure &
temperature at which various states of matter exist for a given substance
Phase equilibrium exists along each line
Normal m.p./b.p.Triple pointCritical pointNote negative slope
for solid-liquidUnique to water
Phase DiagramsA phase diagram is a graph that
gives the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas (vapor).
Lines represent pressures and temperatures at which two phases are in equilibrium