States of Matter

1
States of Matter
2
A Gas

• Uniformly fills any container.
• Mixes completely with any other gas
• Exerts pressure on its surroundings.

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Kinetic Molecular Theory

• 1. Volume of individual particles is ? zero.
• 2. Collisions of particles with container walls
  cause pressure exerted by gas.
• 3. Particles exert no forces on each other.
• 4. Average kinetic energy ? Kelvin temperature of
  a gas.

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Gases

• Particles free of intermolecular forces, flying
  about rapidly in random fashionPhysical
  properties explained by the Kinetic Molecular
  Theory which explains as if the gas were
  ideal a. Gases made of very small particles,
  volume negligible
• compared to volume of the gas b. Particles
  travel at high speeds in straight lines until
  they hit the
• container or another particle c.
  Collisions are completely elastic-no energy
  loss d. No attraction or repulsion between gas
  particles e. Kinetic energy depends on
  temperature, slower and slower as
• temperature drops until at 0 K no
  motion happens
• Real gases only behave like this at high
  temperature and low pressure. Points a, c, and d
  above are not completely obeyed by real gases.

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Grahams Law of Effusion

• Thomas Graham found that gases pass at different
  rates through a small opening into a vacuum. He
  found that the density of the gas determined the
  rate and that in comparing two gases, the square
  root of the ratio of their densities was
  inversely proportional to the ratio of their
  rates. Higher density gases move more slowly.
  This property is important in helping to
  determine the identity of a newly formed gaseous
  compound.

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Diffusion Rates
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Effusion
Diffusion
8
Find the ratio of the effusion rates of UF6
versus H2. Rate H2 MMUF6 352
13.2 Rate UF6 MMH2 2
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Diffusion in the Body

• From high pressure to low pressure areas. Gases
  pass into and out of blood due to differences in
  partial pressure. Oxygen at high pressure goes
  into the blood, carbon dioxide at lower pressure
  in air goes out of the blood. The opposite
  happens at tissues, where oxygen is at lower
  pressure and carbon dioxide is at higher
  pressure. These differences cause the gases to
  travel in the proper directions in the
  appropriate places.

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Pressure

• Pressure is the force of the gas particle
  collision on the walls of their container.
• Pressure units
• mm Hgmillimeters of mercury, which can be held
  up by the pressure of a gas. Atmospheric pressure
  holds up around 760 mm Hg in a barometer.
• Atmospherenormal pressure of earths atmosphere
  1 atm760 mm Hg.
• PSIpound per square inch- English measure used
  in inflation of air filled items. 14.7 psi atm
• Torrnew name for mm Hg in honor of Torricelli,
  inventor of the barometer
• Pascalvery small unit101.3 kPa atm. This unit
  is not used very commonly

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Effect of Atmospheric Pressure
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Standard Pressure Units

• 1 atmosphere
• 760 mm Hg 760 torr
• 1.013 x 105 Pa 101.3 kPa
• 14.7 psi (pounds per square inch)

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Pressure Conversions
The pressure of a gas is measured as 49 torr.
Represent this as atmospheres and as Pascals. 49
torr 1 atm 6.4 x 10-2 atm 760
torr 49 torr 1.013 x 105 Pa 6.5 x 103 Pa
760 torr
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Daltons Law

• John Dalton found that in a mixture of gases,
  each one provides part of the total pressure.
  Ptotal P1 P2 P3 P4 Application of
  this property is in lab collection of gases where
  collecting the gas over water causes some water
  vapor to be included. In this casePtotal Pdry
  gas Pwater The water vapor has to be dealt
  with in order to properly calculate gas density
  to help identify new gases in research.

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Homework-13a

• p. 388 1, 2, 3
• p. 392 4, 5, 6, 9
• p. 415ff 62, 64, 65, 66, 68, 70

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Intermolecular Forces

• Hydrogen bondingH connected to N, O, F is
  partially positive. Attract s to O, N, F on
  another moleculecauses higher melting or boiling
  points than expected in a moleculewater,
  ammonia, proteinsexamples

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London Dispersion Forces

• relatively weak forces that exist among noble gas
  atoms and nonpolar molecules. (Ar, C8H18)
• caused by instantaneous dipole, in which electron
  distribution becomes asymmetrical.
• the ease with which electron cloud of an atom
  can be distorted is called polarizability.

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Intramolecular Forces

• Ionic bondingsalts are made of positive and
  negative particles which hold strongly
  togethersalt, baking soda
• Metallic bondingmetals are thought to be a
  network of metal atoms surrounded by free
  electrons. The degree of attraction between these
  determines melting and boiling points
• Covalent bondsvery strong, forms networks of
  atoms having high melting/boiling pointsdiamond,
  quartz, graphite

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Liquids

• Particles free to move, but still in close
  contact without rigid forces. Attractive forces
  cause several properties1. Viscosityresistance
  to flowing-honey, molasses have high viscosity,
  gasoline has low viscosity. Viscosity is
  inversely proportional to temperature.
• 2. Surface tensionresistance of surface
  particles to expansion of the liquidwater has
  high tension, gasoline very low3.
  Volatilitytendency to evaporate-low forces cause
  liquid particles to escape easily from the
  surface. Evaporation takes heat- which is why
  alcohol feels cold on your skin, taking heat away
  from you. The opposite change is condensation,
  which releases energy as liquid is reformed.4.
  Boiling PointAs temperature increases in a
  liquid , its particles gain energy enough to
  begin breaking past the surface and overcome
  atmospheric pressure. This is the normal boiling
  point.

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Solids

• Molecular attractions strongparticles not free
  to movevibrate in place so that solid has
  definite shape and volume

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Types of Solids

• Amorphousarrangement of particles is not
  regularglass, plastic disorderly
• Crystallinearrangement of particles is regular,
  orderlyquartz, diamond, snowflakes. Caused by
  intermolecular forces

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Types of Crystalline Solids

• Ionic Solid contains ions at the points of the
  lattice that describe the structure of the solid
  (NaCl).
• Molecular Solid discrete covalently bonded
  molecules at each of its lattice points (sucrose,
  ice).
• Atomic Solid individual atoms at the points of
  the lattice (diamond, graphite, network solids)
• Metallic metal atoms at the lattice points,
  attraction due to surrounding free electrons

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Changes in State

• Caused by increase or decrease in kinetic energy
  of particles. When change occurs, it depends on
  the intermolecular forces and the pressure.

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Physical Changes

• Addition of energy causes more vibration, finally
  causing breaking of intermolecular forces and
  bringing it to the melting point. At this melting
  temperature, more energy is added to cause
  complete melting without a gain in temperature.
  This added heat is called heat of fusion.
• Additional energy added raises the temperature of
  the liquid. When it reaches its boiling point,
  the liquid begins to change to gas. As heat is
  added, liquid vaporizes without temperature
  change. This is the heat of vaporization. This
  same energy is released upon condensation.

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Heat of Vaporization
Heat of Fusion
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State Changes

• 1. Condensation/Evaporation LiquidGas
  change2. Melting/Freezing LiquidSolid
  change3. Sublimation Direct GasSolid
  change Sublimation occurs in a freezer when ice
  disappears, when snow disappears without melting
  in the mountains, and dry ice.4. Energy changes
  when states change Exothermicprocess gives up
  energy (condensation, freezing) Endothermicproce
  ss requires energy (melting, evaporation)

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Phase Diagram

• Represents phases as a function of temperature
  and pressure.
• critical temperature temperature above which
  the vapor can not be liquefied.
• critical pressure pressure required to liquefy
  AT the critical temperature.
• critical point critical temperature and
  pressure (for water, Tc 374C and 218 atm).

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Homework-13b

• p. 395 13, 14, 16
• p. 403 17, 21, 22
• p. 409 25, 26
• p.414ff 38, 41, 45, 48, 50, 58, 59

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Laws of Gases Behavior

• Studies of gases led to laws unlike those in
  liquids or solids, gas particles are
  independent and thus have special
  behaviors.

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Boyles LawRelation of Volume and Pressure

• Robert Boyle found that increasing pressure
  causes decrease in volume and vice-versa that is
  that pressure is inversely proportional to
  volume. Lungs demonstrate this diaphragm cause
  pressure differences low pressure causes inhale,
  high pressure cause exhale.Mathematical relation
  PVk In conditions of changing P and V, it can
  be written P1V1 P2V2

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1.53 L of sulfur dioxide gas at 5600 Pa is
changed to 15000 Pa at constant temperature.
What is its new volume? P1V1 P2V2 5600 x
1.53 15000 x V2 V2 0.57 L 1.0 L of
hydrogen gas at 345 torr is connected to an empty
2.5 L flask and allowed to combine. What is its
new pressure? 345 x 1.0 P2 x 3.5 P2
98.6 torr
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Charles LawRelation of Volume to Temperature

• Jacques Charles found that volume varies directly
  with Kelvin temperature so that VkT higher
  temperature causes higher volume. Under changing
  conditions of T and V, equation is V1
  V2 T1 T2

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Balloon with Liquid N2
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Always Change to KELVIN!
K C 273
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A sample of gas at 15o C and 1 atm has a volume
of 2.58 L. What is its new volume at 38o C and 1
atm pressure? Pressure remains constant at 1
atm T1 15 273 288 K T2 38 273 311
K V1 V2 or V1T2 V2T1 T1 T2
2.58 x 311 V2 x 288 V2 2.79 L
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Gay-Lussacs Law

• Pressure is directly proportional to the Kelvin
  Temperature
• P k T
• or P1 P2
• T1 T2

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Homework 14a

• p. 422 1-5
• p. 425 6-8
• p. 427 9-13, 16

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Combined Gas Law

• Both of these can be combined to represent
  changes in all three at once P1V1 P2V2
• T1 T2
• or can be written more easily
• P1V1T2 P2V2T1

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Standard Temperature and Pressure

• STP
• P 1 atmosphere
• T ??C
• The molar volume of an ideal gas is 22.42 liters
  at STP

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A cylinder contains 255 mL of CO2 at 27o C and
812 torr. What volume would this occupy at
STP? P1 812 torr T1 27o C 273 300 K V1
255 mL P2 1 atm 760 torr T2 0o C 273
K P1V1T2P2V2T1 (812)(255)(273)V2(760)(300)
V2 247.9 mL
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Avogadros Law

• For a gas at constant temperature and pressure,
  the volume is directly proportional to the number
  of moles of gas (at low pressures).
• V an
• a proportionality constant
• V volume of the gas
• n number of moles of gas

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Homework 14b

• p. 430 19-23
• p. 432 24-28
• p. 433 29-33

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Ideal Gas Law

• PV nRT
• R proportionality constant
• 0.08206 L atm ??? mol??
• P pressure in atm
• V volume in liters
• n moles
• T temperature in Kelvins
• Holds closely at P lt 1 atm

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Real Gases

• Must correct ideal gas behavior when at high
  pressure (smaller volume) and low temperature
  (attractive forces become important).

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Ideal Gas Laws

• Can be used to calculate molar masses by gas
  density
• density mass molar mass
• volume molar volume
• At STP, molar volume is 22.4 L

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Suppose you have a sample of ammonia gas with a
volume of 856 mL at a pressure of 932 torr and
28o C. What is the mass of the ammonia present?
P 932 torr / 760 torr 1.23 atm V 0.856 L
T 28 273 301 K n PV (1.23)(.856)
0.0426 moles RT (.0821)(301) mass
moles x MM 0.0426 x 17 0.724g
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Ideal Law Rearrangements

• The ideal gas law can be rearranged to find
  density or molar mass of an unknown gas
• d m/V and nm/MM so
• PVnRT becomes n PV/RT
• m/MM PV/RT mPV(MM) /RT
• m/V P(MM)/RT d
• mPV(MM)/RT mRT/PV MM

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Homework 14c

• p. 437 41-45
• p. 438 46-50

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Gas Stoichiometry

• Gases are special in stoichiometry since moles
  are directly proportional to volume. This means
  if a reaction involves relationships between any
  two gases, their mole ratio is the same as their
  volume ratio

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Example 14.9
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Stoichiometry and Gases
When gases and solid are involved, use PVnRT for
moles A sample of solid potassium chlorate
decomposes by the equation 2 KClO3 (s) -----gt
2 KCl (s) 3 O2 (g) If 650 mL of oxygen at 22oC
and 754 torr is collected over water, how much
KClO3 decomposed? PH2O 21 torr (from table of
vapor pressure) Must Subtract Water!!! PO2
754 - 21 733 torr / 760 0.964 atm nO2 PV
/RT (.964)(.650) / (.0821)(295) 0.0259 0.0259
mol O2 2 mol KClO3 122.6 g KClO3 2.11 g
3 mol O2 1 mol KClO3 KClO3
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Homework 14d

• p. 443 60-64
• p448ff 88, 94, 96, 99, 101, 103