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Unit 5: Gases. Physical Properties. Standards. 4a. Students know the random motion of molecules and their collisions with a surface create the observable pressure on the surface 4b. Students know the random motion of molecules explains the diffusion of gases. - PowerPoint PPT Presentation
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Physical Properties
Unit 5: Gases
Standards4a. Students know the random
motion of molecules and their collisions with a surface create the observable pressure on the surface
4b. Students know the random motion of molecules explains the diffusion of gases
A. Kinetic Molecular TheoryUsed to predict and explain the
behavior of a theoretical gas or ‘ideal gas’
Particles in an ideal gas…• have no volume or elastic
collisions• in constant, rapid, random,
straight-line motion• don’t attract or repel each other
‘Ideal gases’- are elastic (do not lose energy upon collision)
Cannot be compressed given a change in temperature
Can be measured using the eq. KE= 1/2mv2
B. Real GasesParticles in a REAL gas…
• have their own volume• attract each other
Gas behavior is most ideal…• at low pressures• at high temperatures• in nonpolar atoms/molecules
C. Characteristics of GasesGases expand to fill any
container• Random constant motion, no
attractionvery low densities
C. Characteristics of Gasescan be compressed given a change
in Temp/Pressure
State Changes
DiffusionThe movement of one material
through another.The rate depends on the mass of
the particlesLighter = rapid diffusion
EffusionWhen a gas escapes through a tiny
openingRate of effusion can be calculated
according to Graham’s law of effusion:
Rate of effusion = 1/SQRT MM
EffusionUsing Graham’s Law, you can also
set up a proportion to compare the diffusion rates for two gases
** see eq on board.
Ammonia has a molar mass of 17.0 g/mol; hydrogen chloride has a molar mass of 36.5 g/mol. What is the ratio of their diffusion?
D. Describing GasesGases can be described by their:
• Temperature• Pressure• Volume• Number of molecules/moles
• K• atm• L• #
E. Temperature
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!
F. Pressure
areaforcepressure
Which shoes create the most pressure?
F. PressureBarometer
• measures atmospheric pressure
exact height of the Hg depends on atmospheric pressure
usually measured in mm Hg
F. PressureManometer
• measures contained gas pressure Difference in
height in two arms of U-tube is measure of pressure of gas sample
measured in various different units
F. Pressure
2mNPa
KEY EQUIVALENT UNITS 101.325 kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
G. STP
Standard Temperature & Pressure
0°C 273 K
1 atm 101.325 kPa-OR-
STP
H. Pressure Problem 1The average pressure in Denver,
Colorado, is 0.830 atm. Express this in (a) mm Hg and (b) kPa.
(a) 0.830 atm1 atm
760 mm Hg = 631 mm Hg
(b) 0.830 atm1 atm
101.325 kPa= 84.1 kPa
H. Pressure Problem 2Convert a pressure of 1.75 atm to
kPa and mm Hg.
(a) 1.75 atm1 atm
101.325 kPa= 177 kPa
(b) 1.75 atm1 atm
760 mm Hg = 1330 mm Hg
H. Pressure Problem 3Convert a pressure of 570. torr to
atmospheres and kPa.
(a) 570 torr760 torr
1 atm = .750 atm
(b) 570 torr760 torr
101.325 kPa= 76.0 kPa