Pressure partial pressure gas stoichiometry
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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

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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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