Pressure Partial Pressure Gas Stoichiometry

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Pressure Partial Pressure Gas Stoichiometry - PowerPoint PPT Presentation

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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PressurePartial PressureGas Stoichiometry

Pressure = Force/Area

Dalton’s Law of Partial Pressures

• Kinetic Molecular Theory
• 5 assumptions
• No definite shape, no definite volume
• Expansion, diffusion, compressibility
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
• 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
• Boxes = length x width x height
• Cylinders = pi x diameter x height
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
• 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
• 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
• STP
• Comparing conditions at 1 atm and 0oC
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
• “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 Pressures
• Pressuretotal = PressureA + PressureB
Finding Partial Pressures
• PressureA = Pressuretotal - PressureB
• 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
• 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
• “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
• “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
• 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?