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Gases Dr. Ron Rusay Summer 2004 © Copyright 2004 R.J. Rusay
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Gases
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Gases: Pressure, Mass, Volume, Temperature
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Pressure Pressure is equal to force/unit area
SI units = Newton/meter2 = 1 Pascal (Pa) 1 standard atmosphere = 101,325 Pa 1 standard atmosphere = 1 atm = 29.92 inches of Hg 34 feet of H2O
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Measuring Atmospheric Pressure Toricellian Barometer
1 standard atmosphere 1 atm = mm Hg 29.92 inches of Hg 34 feet of H2O
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Pressure & Volume Boyle’s Law*
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Changing Volume @ constant temperature P V P V ?
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Pressure & Volume Boyle’s Law*
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Boyle’s Law ** Pressure Volume = Constant (T = constant)
V 1/P (T = constant) (*Holds precisely only at very low pressures.)
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Changing Volume **
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Pressure vs. Volume
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Ideal Gases Real vs. “Ideal” Definition: A gas that strictly obeys Boyle’s Law is called an ideal gas.
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Temperature & Volume (@ constant pressure)
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Temperature & Volume 77 K = ? oC
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Temperature & Volume What happened in the balloon on a molecular level?
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Charles’s Law ** The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin. V = T (P = constant) = a proportionality constant
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Temperature and Volume (@ constant P)
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Pressure vs. Temperature (@ constant V)
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Pressure vs. Temperature (@ constant V)
“Gay Lussac’s Law”
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Vapor Pressure vs. Temperature solid liquid gas
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Pressure, Volume & Temperature
(PV&T)
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Molecular Motion / Theory
The Meaning of Temperature Temperature (Kelvin) is an index of the random motions of gas particles (higher T means greater motion.)
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Standard Temperature and Pressure
“STP” P = T =
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Avogadro’s Law For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures). V = n = proportionality constant V = volume of the gas n = number of moles of gas
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Volume vs. n (moles of a gas)
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Ideal Gas Law ** An equation of state for a gas.
“state” is the condition of the gas at a given time.
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Ideal Gas Law ** PV = nRT Holds closely at P < 1 atm
R = proportionality constant = L atm mol P = V = n = T = Holds closely at P < 1 atm
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Molar Volume at Standard Temperature and Pressure
“STP” P = 1 atmosphere T = C The molar volume of an ideal gas is _____ liters at STP
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Dalton’s Law of Partial Pressures **
For a mixture of gases in a container, (P constant V &T) PTotal = P1 + P2 + P
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