Gases. Particles in an ideal gas… have no volume. have elastic collisions. are in constant,...
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Transcript of Gases. Particles in an ideal gas… have no volume. have elastic collisions. are in constant,...
Gases
Physical Properties
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.
Kinetic Molecular Theory
Particles in a REAL gas…have their own volumeattract each other
Gas behavior is most ideal…at low pressuresat high temperaturesin nonpolar atoms/molecules
Real Gases
Gases expand to fill any container.random motion, no attraction
Gases are fluids (like liquids).no attraction
Gases have very low densities.no volume = lots of empty space
Characteristics of Gases
Gases can be compressed.no volume = lots of empty space
Gases undergo diffusion & effusion.random motion
Characteristics of Gases
Always use absolute temperature (Kelvin) when working with gases.
Temperature
ºF
ºC
K
-459 32 212
-273 0 100
0 273 373
32FC 95 K = ºC + 273
Pressure
area
forcepressure
Which shoes create the most pressure?
Barometermeasures atmospheric pressure
Pressure
Mercury Barometer
Aneroid Barometer
Manometermeasures contained gas pressure
Pressure
U-tube Manometer Bourdon-tube gauge
KEY UNITS AT SEA LEVEL
101.325 kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
Pressure
2m
NkPa
STP
Standard Temperature & Pressure
0°C 273 K
1 atm 101.325 kPa-OR-
STP
Boyle’s Law
In 1662, Robert Boyle discovered that the volume of a gas is inversely proportional to its pressure (at constant temperature).
P
V
Boyles Law
P1V1 = k
P1V1 = P2V2
P1V1 = k = P2V2
K is a constant and has units of L-atm
V
T
Charles’ Law
Charles discovered that the volume and absolute temperature (K) of a gas were related (at constant pressure).
Charles’ Law
V
T
The volume of gases extrapolates to zero at -273 oC or 0 K. When the gases exceed this point the volume calculation would suggest that the gases would have a negative volume.
Charles’ Law
V = bT
V1 T1
= b = V2 T2
V1 T1
V2 T2
=
Combined Gas LawPressure and Temperature are also proportional (at constant volume).By putting all relationships together, it forms the Combined Gas Law.
P1V1 T1
P2V2 T2
=
Avogadro’s LawIn 1811, Avogadro proposed that equal volumes of gases contain equal numbers of particles (at same T, P) It followed that the volume of a gas is proportional to the number of moles.
V1 n1
V2 n2
=
V = na
V1 n1
= a = V2 n2
Ideal gas Law
V = na
V = bT
PV = k Boyle’s law
Charles’s law
Avogrado’s law
At constant T and n
At constant P and n
At constant T and P
Can be combined to form:
PV = nRT
R = 0.08206 L-atm/K-mol
Dalton’s LawThe total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases.
Ptotal = P1 + P2 + ...When a H2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H2 and water vapor.