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 Latm/molK
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.