Download - Kinetic Theory and Gases
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Kinetic Theory and Gases
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Objectives
• Use kinetic theory to understand the concepts of temperature and gas pressure.
• Be able to use and convert between the Celsius and Kelvin temperature scales.
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Kinetic Theory
kinetic theory: all matter is made of particles (atoms,ions, molecules) that are in constant, random motion
kinetic energy (or KE): theenergy of motion; depends on both the mass and speed of the moving particles
temperature (T): a measure of the average KE of allthe particles in a substanceNOT T-E-M-P !
average KE ~ temperature
num
ber o
f pa
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es
Kinetic Theory Applet
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Kelvin Scaleabsolute zero: the coldest possible temperature; there is no molecular motion (= -273oC or 0 Kelvin)
K = oC + 273 oC = K - 273
Kelvin temperature is directly proportional to the KE! 0 K = 0 KE 0 oC ≠ 0 KE600K is 2X more KE than 300K
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Objectives
• Understand the concept of atmospheric pressure.
• Be able to explain how a barometer works.• Be able to convert between pressure
measurements.
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Gases and Pressure
pressure: force applied over an area
PF
A metric pressure unit:
1 pascal (Pa) = 1 N/m2
barometer: instrument that measures atmospheric pressure
14.70 pounds of air push down oneach square inch of the earth’s surface (at sea level) spheres DEMO!
Gases exert pressure by collisions.
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Pressure Conversions
What is the current pressure in kPa and atm?
standard pressure (P)= 14.70 psi = 760.0 mm Hg = 29.92 in Hg = 101.3 kPa= 1.000 atm
standard temperature (T)= 0oC or 273 K
STP: standard T and P
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Objectives
• Be able to use the pressure equation to explain pressure, temperature, and volume changes in gases.
• Understand how to solve word problems using the “GUESS” method.
• Be able to use the various gas laws to solve problems.
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The Gas Laws
PF
A
V
Tk
V
T
V
T
1
1
2
2
Boyle’s Law(constant T)
• force (F) relates to temperature (T)• area (A) relates to volume (V)
P and V are inversely proportional
Charles’s Law(constant P)
P-T Law(constant V)
P V k
P V P V
1 1 2 2
V and T are directly proportional
P and T are directly proportional
P
Tk
P
T
P
T
1
1
2
2
temperature(in K scale)
volume
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Gas Law Problems Using GUESS Method
(1) At constant temperature, 7.5 L of air at 89.6 kPa is compressed to 2.8 L. What is the new pressure? What law was used?
(2) A 3.0 L balloon at 22oC is placed into a freezer at-15oC. What is the new volume if the pressure remainsthe same? What law was used? (3) A fixed volume of gas at STP is heated to 482oC.What is the pressure in kPa at this temperature? What Law was used?
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Objectives
• Understand how the various gas law equations are derived.
• Be able to use the ideal gas law, gas molar mass equation, and gas density equation to solve problems.
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More Gas Laws
P V
n TR
P V n R T
P V
Tk
P V
T
P V
T
1 1
1
2 2
2
Mm
n
nP V
R T
Mm
Mm R T
P V
PVRT
Combined Gas Law
Ideal Gas Law
R = 8.31 kPaL/molK
n = # moles
Gas Molar Mass
Gas Density
DP M
R T
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More Gas Law Problems1. What is the molar mass of a gas that has a mass
of 0.35 g and occupies 165mL at 95oC and 87.0 kPa?
2. How many moles of air are in a 3.2 L balloon under the current temperature and pressure conditions in this room?
3. What is the density of N2 gas at 95 kPa and 25oC?
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Objectives
• Understand Avogadro’s law by considering the ideal gas law.
• Be able to use the law of combining gas volumes to solve simple gas stoichiometry problems.
• Be able to use the ideal gas law to solve more complex gas stoichiometry problems.
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Avogadro’s Law
Avogadro’s Law: equal volumes of gases at the sameT and P contain equal numbers of molecules (n)
O2 He CO2
Why? Look at theIdeal Gas Law!P V n R T
nP V
R T
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Law of Combining Gas Volumes
N2(g) + 3H2(g) → 2NH3(g)
Coefficients can represent gas volumes if thereactants and products are at equal T and P.
1 vol. 3 vol. 2 vol. 1 L 3 L 2 L
How many liters of H2 are needed to completelyreact with 2.5 L N2? Assume same T and P.
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Gas Stoichiometry
g A → mol A → mol B → g B
g A → mol A → mol B → L B (use V = nRT/P)
(1) How many liters of CO2 at 23oC and 89.5 kPa areformed when a 468 g container of C3H8 is burned?(2) How many liters of H2 gas are formed when 0.25 gNa reacts with HCl at STP?