Gases

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					Gases
Kinetic Molecular Theory
 Particles   of matter are in constant motion
 Thestate of a substance at room
 temperature depends on the strength of
 the intermolecular forces between the
 particles.
5 assumptions of Kinetic Theory
 1. gases are tiny particles
 2. particles have elastic collisions with
  each other
 3. particles in constant motion
 4.no forces between particles
 5. speed of particles determined by
  temperature
Bonding (Intramolecular)
ionic bond- transfer of electrons
            between cation (+) and anion(-
  )
Subtract electronegativities to predict bond
  type
 Covalent   bond- sharing of electrons
    Nonpolar- equal sharing of electrons
    Polar –unequal sharing of electrons
 Polarmolecule has a slightly + and – side
 due to the difference in
 electronegativities of the elements
 involved.
Intermolecular forces
 Occur between 2 molecules (polar
  covalent)
 3 major types: 1.dispersion
    2. dipole to dipole   3. hydrogen bond
 Dispersion   force- temporary and weak
    strong polar molecule causes a nonpolar
   molecule to become slightly polar
 Dipole   to Dipole
   slightly + end of one molecule is
  attracted to the slightly – end of another
  molecule
 Shape can cancel out polarity
 Hydrogen    bond- attraction between
 molecules
    Uses H,F, O, N. (generally the strongest
     attraction)
          expansion, diffusion occur due to
 Fluidity,
  the weak or none attraction between
  molecules
 Which states of matter have these
  properties?
 Which   diffuses faster?
    High molar mass or low molar mass?
    Polar or nonpolar molecules?
    High IMF or low IMF?
 Idealgases have NO attraction between
  molecules
 Real gases have some attraction
  between molecules
A  change of state occurs when IMF are
  formed or broken
 Increase in heat?
 Decrease in heat?
 Changing    gases into liquids
    Increase pressure
    Decrease temperature
    This causes increase in IMF
 IdealGases are gases that follow the
 Kinetic Molecular theory
     Gases (all gases) deviate from the
 Real
 KMtheory
 Gasesbehave more ideally when?
   what pressure?
   what temperature?
3   categories of gases
      Noble  gases
      Nonpolar gases
      Polar gases
Noble Gases
 Have   an octet
    How  many valence electrons?
    Attract electrons?  Why?
Nonpolar gases
 nonpolar   bonding– equal sharing of
  electrons
 Example– diatomics
    List these?
    Do these gases form IMF with other
     molecules?
    Why?
Polar Gases
 Polar bonding- unequal sharing of
  electrons
 Form IMF with other molecules
 Examples- ammonia (NH3)     Water vapor
 Pressure-  force/area
     units of pressure- these are equivalent
 1 atmosphere (atm)
 760 torr
 760 mmHg
 101.3 kpascal
Convert 2.25 atm=_______ mmHg

895 mmHg = ______ atm

850 mmHg = _____ torr
Temperature
 Temperature    must use the kelvin scale
 Kelvin scale is based on absolute zero
     Particles are motionless
 Measure    in celsius and convert to kelvin
   C + 273 = kelvin
   Kelvin – 273 = celsius
STP
 Standard   temperature 273 kelvin or 0 c
 Standard Pressure= 1 atm
 STP is used to compare gases and results
Boyles Gas Law
 Pressurevaries inversely with volume
 Pressure increases volume _______
 Volume increases  pressure ______
 Formula      P1V1 = P2V2
    Charles Gas Lawtemperature
       is directly related to
 Volume
  volume increases temperature _____
 Temperature increases  volume ________
 Formula :
Gay Lussac Gas Law
 Pressure is directly related to temperature
 Increase in temperature  ____ pressure
 Increase in pressure  _______
  temperature
 Formula:
Combined Gas Law
      into consideration all 3 variables
 Takes
 (Page 375 in your book)
    Formula:
Problem
 What is the new volume at STP if the gas
 that was originally collected at a pressure
 of 795 mmHg and a temperature of 30 C
 has a volume of 355 mL?
problem
A gas was collected at 1.65 atm with a
 volume of 65.0 ml, what is the new
 volume if the pressure is changed to 2.00
 atm? The temperature remains constant.
Dalton’s Law of partial
pressures
 Total pressure of the gas is equal to the
  sum of all of the pressures.
 PT= P1 + P2 + P3
Collected over Water
 PT= Pgas + Pwater
 Pgas = Ptotal - Pwater


 Water table of the back of Periodic Table
 Page 859
      volumes of gases at the same temperature
 Equal
    Avogadro’s Law
 and pressure contain equal numbers of molecules
 Standard    Molar Volume of a gas at STP is
    22.4 liter/mole   regardless of the gas
All collected at STP
 2.67   moles of an unknown gas = ______
  liters
 3.56 liters of gas = __________ moles
Molar mass          g/mole
A  gas has a mass of .953 grams with a
 volume of 333 mL. What is the molar mass
 of this gas at STP? (remember must use
 liters)
     grams of an unknown gas has a
 .334
 volume of 250 mL when collected at STP.
 What is the molar mass of this gas?

				
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