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Pressure Partial Pressure Gas Stoichiometry

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PressurePartial PressureGas Stoichiometry

Pressure = Force/Area

Dalton’s Law of Partial Pressures

Avogadro’s Law

- Kinetic Molecular Theory
- 5 assumptions

- No definite shape, no definite volume
- Expansion, diffusion, compressibility

- 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?

- 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

- Boxes = length x width x height
- Cylinders = pi x diameter x height

- 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

- 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

- 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

- STP
- Comparing conditions at 1 atm and 0oC

- 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

- “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

- Pressuretotal = PressureA + PressureB

- 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

- 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

- “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

- “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

- 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?