gases. kinetic molecular theory particles in an ideal gas… –have no volume. –have elastic...
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Kinetic Molecular Theory
• Particles in an ideal gas…– have no volume.– have elastic collisions. – are in constant, random, straight-line
motion.– don’t attract or repel each other.– have an avg. KE directly related to Kelvin
temperature.
C. Johannesson
Temperature= how fast the molecules are moving
ºF
ºC
K
-459 32 212
-273 0 100
0 273 373
32FC 95 K = ºC + 273
• Always use absolute temperature (Kelvin) when working with gases.
STP
Standard Temperature & PressureStandard Temperature & Pressure
0°C 273 K
1 atm 101.3 kPa-OR-
STP
V = volume = how much space a gas occupies
Units– L, mL, cm3
– 1000 mL = 1 L, 1 mL = 1 cm3
n = moles = how much gas there is
R = ideal gas constant • = 0.0821 (L*atm) (mol*K) • = 8.31 (L*kPa) (mol*K)
Charles’ Law
• T V (temperature is directly proportional to volume)• T ↑ V↑ & T↓ V↓
• V1 = V2
T1 T2 T is always in K– P and n = constant
• Ex) A 25 L balloon is released into the air on a warm afternoon (42º C). The next morning the balloon is recovered on the ground. It is a very cold morning and the balloon has shrunk to 22 L. What is the temperature?
V
T
CharlesLaw.exe
240 K, 33 °C
Boyle’s Law• P↓ V ↑ & P↑ V ↓• P 1/V (pressure is inversely proportional to volume)
• P1V1 = P2V2– T and n = constant
Ex: Pressure: 0.98 atm 0.92 atmVolume: ? mL 8.0 L
P
V
Boyle'sLaw.exe
7.5 L
AVOGADRO’S LAW• Vn Vn • V n (direct)
• V1 = V2
n1 n2
– T & P Constant
EX: A 3 liter sample of gas contains 3 moles. How much gas will there be, in order for the sample to be 2.3 liters? P & T do not change
Avogadro'sLaw.exe
2.3moles
Gay-Lussac’s Law
• P1 = P2
T1 T2
– V & n constant
• Direct relationship
• PT PT
P
T
Gay-Lussac'sLaw.exe
Example: A can of Dust Off is sitting next to my computer at 25°C and 3.5 atm. I flip the can over and spray some air out. The room has a pressure of 1.0 atm. What is the temperature of the air as it escapes the container?
http://www.youtube.com/watch?v=4qe1Ueifekg2.06 min
85 K, - 188 °C
COMBINED IDEAL GAS LAW
• P1V1 = P2V2
n1T1 n2T2
• If P, V, n, or T are constant then they cancel out of the equation.
• n usually constant (unless you add or remove gas), so
• P1V1 = P2V2
T1 T2
Ideal Gas Law (“Pivnert”)• PV = nRT
• R = ideal gas constant • = 0.0821 (L*atm)
(mol*K)
• = 8.31 (L*kPa)
(mol*K)
Ideal Gas Law (“Pivnert”)
PV=nRT R = The Ideal Gas Constant (memorize)R = 0.0821 (L*atm) (mol*K) R = 8.31 (L*kPa) (mol*K)* Choose which R to used based on the units of your pressure. If you have mmHg change it to atm.* V has to be in Liters, n in Moles, T in Kelvin, P can be in atm or kPa
P V = n R T (atm) (L) = (moles) (L*atm/mol*K) (K)(kPa) (L) = (moles) (L*kPa/mol*K) (K)
Dalton’s Law of Partial Pressure• The total pressure of a mixture of gases is
equal to the sum of the partial pressures of the component gases.
• Ptotal = Pgas 1 + Pgas 2 + P gas 3 + …
• Example: Find the total pressure for a mixture that contains three gases. The partial pressure of nitrogen is 15.75 kPa, helium is 47.25 KPa, and oxygen is 18.43 kPa.
81.43 kPa