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Pressure Partial Pressure Gas Stoichiometry. Pressure = Force/Area Dalton’s Law of Partial Pressures Avogadro’s Law. What do we already know?. Kinetic Molecular Theory 5 assumptions No definite shape, no definite volume Expansion, diffusion, compressibility. Question.

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pressure partial pressure gas stoichiometry

PressurePartial PressureGas Stoichiometry

Pressure = Force/Area

Dalton’s Law of Partial Pressures

Avogadro’s Law

what do we already know
What do we already know?
  • Kinetic Molecular Theory
    • 5 assumptions
  • No definite shape, no definite volume
  • Expansion, diffusion, compressibility
question
Question
  • By the end of the lecture try to answer the question:
  • At the same temperature and volume, why do larger gas molecules exert more pressure on their container?
volume
VOlume
  • Gas particles will take on the volume of the container they are in
  • To measure the volume of the gas, measure the volume of the container it is in
volume measurements
Volume MEasurements
  • Boxes = length x width x height
  • Cylinders = pi x diameter x height
pressure
Pressure
  • Pressure is the force exerted over an area
  • Force is measured in Newtons (N)
  • The Force of gas particles is created by the moving gas particles hitting the sides of their container
measuring pressure
Measuring Pressure
  • Pressure is measured with a barometer
  • The first barometer measured pressure by measuring how high a gas could raise a column of mercury, thus the units of pressure were:
    • mm of Hg
units of pressure
Units of Pressure
  • Like there are different ways to measure weight or length, there are different ways to measure pressure
  • Torr is equal to 1 mm of Hg
  • The SI unit for pressure is Pascal (Pa)
    • 1 pascal = 1 N/m2
    • The kilopascal (kPa) is also used
  • The most widely used unit is the atmosphere (atm)
      • it is the average atmospheric pressure at sea level and 0oC
standard temperature and pressure
Standard Temperature and Pressure
  • STP
  • Comparing conditions at 1 atm and 0oC
unit conversions
Unit conversions
  • 1 atm =
    • 760 mm Hg =
    • 760 torr =
    • 1.013 x 105 Pa =
    • 101.3kPa

1atm

760 mm Hg

760 torr

101.3kPa

101.3kPa

101.3kPa

760 mm Hg

1.013 x 105 Pa

760 torr

1.013 x 105 Pa

1.013 x 105 Pa

1atm

1atm

760 torr

dalton s law of partial pressures
Dalton’s Law of Partial Pressures
  • “The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases”
  • What does this mean?
  • Remember that we assume that gas molecules are not affected by each other
  • Therefore, each type of molecule will act independently of any other type
  • To find the total pressure, we just add the pressures of the individual types of molecules together
dalton s law of partial pressures1
Dalton’s Law of Partial Pressures
  • Pressuretotal = PressureA + PressureB
finding partial pressures
Finding Partial Pressures
  • PressureA = Pressuretotal - PressureB
partial pressures last comments
Partial Pressures Last Comments
  • Partial pressures must be in the same units to be compared
  • The number of pressures in a mixture does not affect the Dalton’s law of partial pressures equation
stoichiometry of gases
Stoichiometry of Gases
  • What do we already know about stoichiometry?
  • Using chemical equations to know the ratios between different compounds
  • N2H4 + 2H2O2 -> N2 + 4H2O
  • 1 mol N2H4 for 2 mol H2O2
  • 1 mol N2H4 for 1 mol N2
  • 1 mol N2H4 for 4 mol H2O
  • 2 mol H2O2 for 1 mol N2
  • 2 mol H2O2 for 4 mol H2O
  • 1 mol N2 for 4 mol H2O
avogadro s law
Avogadro’s Law
  • “equal volumes of gases at the same temperature and pressure contain equal numbers of molecules”\
  • What does this mean?
  • H2(g) + Cl2(g) -> 2HCl(g)
    • 1 mol H2 = 1 mol Cl2 = 2 mol HCl
    • 1 molecule H2 = 1 molecule Cl2 = 2 molecules HCl
    • 1 Volume H2 = 1 volume Cl2 = 1 volumeHCl
standard molar volume
Standard Molar Volume
  • “the volume occupied by 1 mol of a gas at STP”
  • What does this mean?
    • At standard temperature and pressure (STP) 1 mol of gas will always occupy the same volume
  • 22.4 L / 1 mol at STP
  • This is a conversion factor you have seen before
review
Review
  • Pressure is Force over area
  • The partial pressures of a mixture of gases are added together to form the total pressure of the mixture
  • Avogadro’s law compares mols, volumes, and molecules of gases in a balanced chemical equation
  • At STP, 1 mol of gas occupies 22.4 L
  • At the same temperature and volume, why do larger gas molecules exert more pressure on their container?
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