BEHAVIOR OF GASES
diffusion –


effusion When comparing 2 gases we use Graham’s Law of Effusion and the equation below:
Rate
Graham’s Law of Effusion -
A
=
Rate
B
PRESSURE
partial pressure –
Dalton’s Law of Partial Pressures Ptotal =
for air:
Pair =
PRESSURE vs MOLES (n)
1 mol
(1 L)
2 mol
(1 L)
If
of a gas (in 1 L vol.) exerts
of a gas (in 1 L vol.) exerts
2x as many particles 
More moles (particles) of gas 
pressure,
pressure.
PRESSURE vs VOLUME
(at constant temperature)
P (atm)
Start with
vol.
1 L at 1 atm
pressure
V= 1L
P = 1 atm
V=
P=
as volume
pressure
V (L)
vol.
pressure
V=
P=
as volume
pressure
As volume decreases
BOYLE’S LAW –
VOLUME vs TEMPERATURE (at constant pressure)
heat
Start with
1 L at 100 K
temp.
vol.
T = 100 K
V = 1L
T=
V=
as temp.
volume
CHARLES’ LAW –
cold
temp.
vol.
T=
V=
as temp.
volume
As temp. increases
PRESSURE vs TEMPERATURE (at constant volume)
As temperature rises
Start with
heat
100 K and 1 atm
cold
T
T
P
T = 100 K
P = 1 atm
P
T=
P=
T=
P=
as temp.
pressure
as temp.
pressure
GAY-LUSAAC’S LAW –
COMBINED GAS LAW
When using the combined gas law
IDEAL
and temperatures must be in
vs
REAL GASES
Real gases do not behave as ideal gases at
because
therefore
(Gas Law equations
)
MOLES MEET GAS LAWS
pressure of a gas is proportional to
~
volume of a gas is proportional to
~
pressure of a gas is proportional to
~
volume of a gas is proportional to its
~
Now we solve
using the values for
Substituting into the equation we get:
of a gas at
(
(
)(
)(
~
.
) =
)
IDEAL GAS LAW
When using the Ideal Gas Law
P must be in
V must be in
n must be in
T must be in
1. 0.05 moles of a gas at a temp. of 20oC is contained in a 150 ml vessel. What is the pressure?
P=
V=
n=
R=
T=
2. How many grams of bromine gas at –10oC and 1277 mm Hg would be in 3000 ml vessel?
P=
V=
n=
R=
T=
3. 110 g of carbon monoxide at a pressure of 35.4 in. Hg and a volume of 782 ml would be at
what temperature in Celsius?
P=
V=
n=
R=
T=
DENSITY & MOLECULAR WEIGHT
(D & MW)
Density =
(D)
Molecular Weight =
(MW)
For gases:
(at STP =
1. What is the density of a gas with a mass of 28 g and a volume of 31 L? What is its MW?
2. Calculate the molecular weight of a gas with a mass of 4.50 g and a volume of 6800 ml.
3. What is the density of oxygen gas at STP?
4. Calculate the density of sulfur trioxide gas at STP.
Replacing volume with density in the Combined Gas Law we get:
5. What is the density of oxygen gas at – 20oC and 1.2 atm of pressure?
STP:
D1 =
D2 =
D1 at STP =
P1 =
P2 =
T1 =
T2 =
6. What is the density of a gas at STP if its density is 2.54 g/L at 10oC and 16 psi?
STP:
D1 =
D2 =
P1 =
P2 =
T1 =
T2 =
)
EUDIOMETER PROBLEMS
eudiometer –
-
When a gas is collected over water
gas collected
-
The amount of water vapor
(see table)
water
The eudiometer reading is therefore
When performing eudiometer problems we must adjust for:
1.
To convert
(
2.
To correct
Ex: A eudiometer tube contains 38.4 ml of hydrogen gas, collected by water displacement at 20 oC.
The water level inside the tube is 140 mm higher than that outside. The barometer reading is
749 mm. Calculate the volume of dry hydrogen gas at STP.
a. correction for water / mercury difference:
b. correction for difference in levels:
c.
correction for water vapor: (use table)
d. solve the equation for volume at STP :
V1 =
V2 =
P1 =
P2 =
T1 =
T2 =
)
DENSITY & MOLECULAR WEIGHT
Density = mass = m = g
(D)
volume
V
L
(cont’d)
Ideal Gas Law:
PV= nRT
R = .0821 L atm/mol K
We can also use the Ideal Gas Law to solve for density at conditions other than standard
by substituting m/D for volume in PV= nRT this equation becomes:
1. Use the Ideal Gas Law to find the density of diphosphorous pentoxide at
127oC and 768 mm Hg.
P=
m=
GFM =
n=
T=
D=
2. Use the Ideal Gas Law to find the density of carbon monoxide at 60oC and 730 mm Hg.
3. Use the Ideal Gas Law to find the density of uranium hexafluoride at 220oC and 45 psi.