States of Matter

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States of Matter
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Common States of Matter

• Gases
• What do you know about gases?
• Liquids
• What do you know about liquids?
• Solids
• What do you know about solids?
• States of matter phet

3
Kinetic Molecular Theory
The KMT relates the kinetic energy of molecules
to states of matter.
Intro to KMT
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The Nature of GasesKinetic 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 motion
• 3. Collisions are perfectly elastic
• 4. Do not attract or repel one another
• 5. Average Ek is proportional to absolute temp

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Movement of Gas Particles in a Container
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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

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Atmospheric Pressure
Atmospheric pressure is due to the force of
atmospheric gases colliding with objects and
weight of atmospheric gases.
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Barometer

• Measures atmospheric pressure
• Invented by Alejandro Torricelli
• Patm presses down on the surface, forces Hg up
  into the tube

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Units of Pressure

• Pascal (SI unit) Pa
• Millimeters of Hg mmHg
• Atmosphere atm
• Torr torr
• Conversion factors _at_ 25C Know these!
• 1 atm 760 mmHg 760 torr 101.3 kPa 14.7
  psi

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Converting Between Units of Pressure

• Convert a pressure of 385 mmHg to kilopascals
  (kPa)
• How would you do it?
• 51.3 kPa

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Kinetic Energy Temperature
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13.2 The Nature of Liquids

• Both liquids and gases are fluids, i.e. they can
  flow

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13.2 The Nature of Liquids

• Key difference from gases
• Molecules are close enough to have intermolecular
  forces of attraction
• This is why liquids have a definite volume
• But not close enough to fix them in place
• This is why molecules of liquids can move past
  one another (flow)
• Condensed matter
• Liquids and solids are known as condensed phases
  of matter

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Evaporation
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Evaporation

• Vaporization the conversion of a liquid to a
  gas or vapor
• Evaporation vaporization occurring at the
  surface of a liquid
• During evaporation, molecules of liquid with
  sufficient KE escape in to the vapor phase
• In 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
  condensation
• What would happen to the rate of evaporation when
  a liquid is heated? Why?

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Vapor Pressure
13.2

• Vapor pressure is a measure of the force exerted
  by a gas above a liquid.

States of matter phet
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Vapor Pressure

• In a closed container, as molecules escape into
  the vapor phase, pressure builds
• This is vapor pressure
• At a certain pressure, the rate of vaporization
  equals the rate of condensation
• This is an example of dynamic equilibrium
• Then vapor pressure is constant
• Vapor Pressure Simulation

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Vapor Pressure

• Depends upon the liquid
• Depends upon temperature

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Vapor Pressure

• Depends upon the liquid
• Depends upon temperature

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Boiling Point

• A 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.

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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?

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13.3 Solids

• Crystal Structure
• Simple cubic
• Body centered cubic
• Face centered cubic
• Allotropes
• Amorphous solids
• Glasses

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Some Types of Unit Cells
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Allotropes

• Allotropes are varying forms of an element
• Example oxygen (O2) and ozone (O3)
• Example allotropes of carbon

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Non-Crystalline Solids

• Amorphous solids lack an ordered internal
  structure.
• Examples rubber, plastic, asphalt, glass

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13.4 Changes of State

• Vaporization/Condensation
• Liquid ? Gas
• Evaporation
• Boiling
• Vapor vs. Gas
• Melting/Freezing
• Liquid ? Solid
• Solidification
• Sublimation/Deposition
• Solid ? Vapor
• I2 (s) ? I2 (g)

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Sublimation

• Solid ? Vapor
• Sublimation occurs in solids with vapor pressures
  that exceed atmospheric pressure at or near room
  temperature.
• Deposition
• Vapor ? Solid

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Phase Diagrams

• Show 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 point
• Critical point
• Note negative slope for solid-liquid
• Unique to water

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Phase Diagrams

• A 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