I. Physical Properties of Gases
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Transcript I. Physical Properties of Gases
Gases
Gases
I. Physical
Properties
A. Characteristics of Gases
expand
to fill any container
fluids
(like liquids)
have
very low densities
A. Characteristics of Gases
can
be compressed
undergo
diffusion & effusion
B. Temperature
always
use KELVIN when working
with gases
ºF
-459
ºC
-273
K
0
C 59 F 32
32
212
0
100
273
373
K = ºC + 273
C. Pressure
force
pressure
area
Which shoes create the most pressure?
C. Pressure
barometer
• measures atmospheric pressure
Mercury Barometer
Aneroid Barometer
C. Pressure
manometer
• measures contained gas pressure
U-tube Manometer
Bourdon-tube gauge
C. Pressure
KEY
UNITS AT SEA LEVEL
101.325 kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
D. STP
STP
Standard Temperature & Pressure
0°C
273 K
-OR-
1 atm
101.325 kPa
Gases
II. The Gas
Laws
A. Boyle’s Law
P1V1 = P2V2
inverse relation!
example:
car engine cylinder
breathing
P
V
A. Boyle’s Law
B. Charles’ Law
V1 = V2
T1 T2
proportional
relation!
V
T
example:
hot air balloons
B. Charles’ Law
C. Gay-Lussac’s Law
P1 = P2
T1 T2
proportional
relation!
P
T
example:
autoclave
(sterlization)
D. Combined Gas Law
P 1V 1
T1
=
P 2V 2
T2
P 1V 1 T 2 = P 2V 2T 1
E. Gas Law Problem #1
A gas occupies 473 cm3 at 36°C.
Find its volume at 94°C.
E. Gas Law Problem #2
A gas occupies 100. mL at 150.
kPa. Find its volume at 200. kPa.
E. Gas Law Problem #3
A gas occupies 7.84 cm3 at 71.8 kPa &
25°C. Find its volume at STP.
E. Gas Law Problem #4
A gas’ pressure is 765 torr at 23°C.
At what temperature will the
pressure be 560. torr?
Gases
Ideal Gas Law
Avogadro’s Principle
CO2
Ne
Equal volumes of gases contain
equal numbers of moles
• at constant temp & pressure
• true for any gas
V
n
Ideal Gas Law
PV=nRT
UNIVERSAL GAS CONSTANT
R=0.0821 Latm/molK
Ideal Gas Law Problem #5
Calculate the pressure in atmospheres
of 0.412 mol of He at 16°C & occupying
3.25 L.
Ideal Gas Law Problem #6
Find the volume of 85 g of O2 at 25°C
and 104.5 kPa.
Gases
Gas Stoichiometry at
Non-STP Conditions
Gas Stoichiometry
STP: moles liters of a gas:
• use 22.4 L = 1 mol
How many moles are in a 4.5 L helium
balloon at STP?
at
Gas Stoichiometry
STP: moles liters of a gas:
• use 22.4 L = 1 mol
__H2 + __O2 __H2O
How many grams of water can be
formed if you start with 2.3 L of H2?
at
Gas Stoichiometry
at
non-STP
• given liters of gas?
start with ideal gas law
• looking for liters of gas?
start with stoichiometry conv.
Gas Stoichiometry Problem
What volume of CO2 forms from the
decomposition of 5.25 g of CaCO3 at 103
kPa & 25ºC?
CaCO3
CaO
+
CO2
Gas Stoichiometry Problem
What volume of CO2 forms from
5.25 g of CaCO3 at 103 kPa & 25ºC?
Gas Stoichiometry Problem
How many grams of Al2O3 are formed from
15.0 L of O2 at 97.3 kPa & 21°C?
4 Al
+
3 O2
2 Al2O3
Gas Stoichiometry Problem
How many grams of Al2O3 are formed
from 15.0 L of O2 at 97.3 kPa & 21°C?
4 Al
+
3 O2
2 Al2O3
Gases
Two More Laws
Dalton’s Law
The total pressure of a mixture
of gases equals the sum of the
partial pressures of the
individual gases.
Ptotal = P1 + P2 + ...
When H2 gas is collected
by water displacement,
the gas in the collection
bottle is actually a mixture
of H2 and water vapor.
Dalton’s Law
Hydrogen gas is collected over water at
22.5°C. Find the pressure of the dry gas
if the atmospheric pressure is 94.4 kPa.
Dalton’s Law
A gas is collected over water at a temp of 35.0°C
when the barometric pressure is 742.0 torr.
What is the partial pressure of the dry gas?
Graham’s Law
diffusion
• spreading of gas molecules
throughout a container until evenly
distributed
effusion
• passing of gas molecules through
a tiny opening in a container
Graham’s Law
speed
of diffusion/effusion
• KE is determined by temp of gas
• at same temp & KE, heavier
molecules move more slowly
Graham’s Law
Graham’s
Law
• rate of diffusion of a gas is inversely
related to square root of molar mass
vA
vB
mB
mA
Graham’s Law
Determine
the relative rate of diffusion
for krypton and bromine.
Graham’s Law
A molecule of oxygen gas has an average
speed of 12.3 m/s at a given temp and pressure.
What is the average speed of hydrogen
molecules at the same conditions?
Graham’s Law
An unknown gas diffuses 4.0 times faster than
O2. Find its molar mass.