Pressure Partial Pressure Gas Stoichiometry Pressure = Force/Area Dalton’s Law of Partial...
Transcript of Pressure Partial Pressure Gas Stoichiometry Pressure = Force/Area Dalton’s Law of Partial...
PressurePartial Pressure
Gas StoichiometryPressure = Force/AreaDalton’s Law of Partial
PressuresAvogadro’s Law
What do we already know?
• 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
1.013 x 105 Pa
101.3kPa
760 mm Hg101.3kPa
1.013 x 105 Pa
760 torr
760 torr
1atm 1atm
1.013 x 105 Pa
101.3kPa
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 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• 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• “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?