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1
Chapter 5: GASES
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Chapter 5: GASES
In this chapter we will:
Define units of pressure and volume Explore the properties of gases Relate how the pressure, volume,
and temperature of gases are related
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Characteristics of Gases
Uniformly fills any container. Are highly compressible Mixes completely with any other
gas Exert pressure on its
surroundings.
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Pressure
Pressure is the force acting on an
object per unit area: P = F/A
Gravity exerts a pressure on the earth’s
atmosphere
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Pressure
The pressure of a 1 m2 column of air on earth exerts a pressure of about 100 kPa
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Units of Pressure
SI units = Newton/meter2 = 1 Pascal (Pa)
101,325 Pa = 101.325 kPa =
1 atmosphere = 1 atm
1 atm = 760 mm Hg = 760 torr
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PressureAtmospheric Pressure and the Barometer
Atmospheric pressure is measured with a barometer.
Standard atmospheric pressure is the pressure required to support 760 mm of Hg in a column
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Units of Pressure
The manometer above is another tool used to measure pressure. How would you measure how much pressure is being exerted on the column of mercury?
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Gas Laws: Boyle’s Law
The volume of a fixed quantity of gas is inversely proportionalto its pressure
Pressure Volume = Constant (T = constant)
P1V1 = P2V2 (T = constant)
V 1/P (T = constant)
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Gas Laws: Boyle’s Law
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Gas Laws: Charles’s Law
The volume of a gas is directly proportional to temperature
V = constant • T (P = constant)V/T = constant
VT
VT
P1
1
2
2 ( constant)
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Gas Laws: Charles’s Law
The plot of V vs. T is a straight line. What does that tell us about the relationship between V and T?
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Gas Laws: Gay-Lussac’s Law Gay-Lussac’s Law
Gay-Lussac’s Law of Combining Volumes:Gay-Lussac’s Law of Combining Volumes:
at a given T and P the volume of gases which react are small whole number ratios.
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Gas Laws: Avogadro’s Law
For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas
V = constant • n
n = number of moles of gas
22.4 L of any gas at 0° C contains 6.02x1023 gas molecules
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The Meaning of Temperature
Temperature measures the average kinetic energy of atoms (higher T means greater motion.)
We use the Kelvin temperature scale as an index of the random motions of gas particles.
(KE)32avg RT
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Standard Temperature and Pressure
“STP” P = 1 atm T = 0C = 273 K The molar volume of an ideal gas is
22.42 liters at STP
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The Ideal Gas Law
An equation of state for a gas. “state” is the condition of the gas at a
given time.PV = nRT
R = Ideal Gas constant = 0.08206 L atm mol
P = pressure in atm
V = volume in liters
n = moles
T = temperature in Kelvins
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The Ideal Gas Law
Sample Exercise: A sample of H2 has a volume of 8.56 L at a temperature of 0° C and a pressure of 1.5 atm. Calculate the moles of H2 molecules present in this gas sample.
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The Ideal Gas Law
Sample Exercise 2: A sample of gas contains 0.35 mol of argon gas at a temperature of 13°C and a pressure of 568 torr is heated to 56°C and a pressure of 897 torr. Calculate the change in volume that occurs.