Gas Laws and Properties: Understanding the Behavior of Gases
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The sum of the individual gas pressures
equals the overall pressure of the mixture of
gases.
If a container has 166 torr H
2
, 109 torr CO
2
and 176 torr of O
2
, what is the total pressure
of the mixture?
166 torr + 109 torr + 176 torr = 451torr
Our atmosphere is made of 21% O
2
, 78% N
2
and 1% other gases. At sea level (standard
pressure), what is the partial pressure of
oxygen?
760 torr x 0.21 = 159 torr O
2
52.5 mL of gas is collected over water at 20
o
C
and 100.0 kPa. What is the pressure of the
dry gas?
100.0 kPa = P
gas
+ P
water
P
water
at 20
o
C = 2.3 kPa
100.0 kPa – 2.3 kPa = 97.7 kPa
@STP what would the volume of the gas be?
Which law would we have to use?
◦
Combined Law
P
1
= 97.7 kPa
V
1
= 52.5 mL
T
1
= 20
o
C + 273K = 293K
P
2
= 101.3 kPa
V
2
= ?
T
2
= 273 K
V
2
= 47.2 mL
The spontaneous spreading of particles
The rate of diffusion depends on the
velocities and masses of the molecules
Effusion
– the process by which a gas escapes
from a small hole in a container
Lighter gases
ALWAYS
diffuse/effuse
faster
than heavier molecules
The relative rates at which two gases, at the
same temperature and pressure, will diffuse,
vary inversely as the square root of the
molecular mass of the gases.
**Always
consider gas 1
the lighter gas
Compute the relative rates of diffusion of
helium and argon.
◦
go to the periodic table for molar mass of He and Ar
Mass He = 4 g/mol
Mass Ar = 40 g/mol
So, helium
diffuses 3x’s
faster than argon.
Compare the rates of diffusion of O
2
and N
2
.
Since the lighter gas always diffuses
faster, N
2
diffuses 1.07x’s faster than O
2
Compare the rates of diffusion of sulfur
trioxide and nitrogen monoxide.
NO diffuses 1.63x’sfaster than SO
3
Gas #1 weighs 42.0 g/mol and diffuses at a
rate of 5.65 m/s through an opening in a jar.
Gas #2 weighs 252.0 g/mol. At what rate
would it pass through the same opening?
v
2
= 2.31 m/s
Gas laws govern the behavior of gases and their properties in various conditions. From the total pressure of gas mixtures to calculating partial pressures, understanding the relationship between pressure, volume, temperature, and amount of gas is crucial. Effusion and diffusion play key roles in how gases spread. The relative rates of diffusion are inversely proportional to the square root of the molecular mass, with lighter gases diffusing faster.
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Presentation Transcript
The sum of the individual gas pressures equals the overall pressure of the mixture of gases. + + + = ....... P P P total P 1 2 3
If a container has 166 torr H2, 109 torr CO2 and 176 torr of O2, what is the total pressure of the mixture? 166 torr + 109 torr + 176 torr = 451torr
Our atmosphere is made of 21% O2, 78% N2 and 1% other gases. At sea level (standard pressure), what is the partial pressure of oxygen? 760 torr x 0.21 = 159 torr O2
Temperature 0oC 20oC 40oC 60oC 80oC 100oC Temperature Pressure 0.6 kPa 2.3 kPa 7.4 kPa 19.9 kPa 47.3 kPa 101.3 kPa Pressure
52.5 mL of gas is collected over water at 20oC and 100.0 kPa. What is the pressure of the dry gas?
100.0 kPa = Pgas + Pwater Pwater at 20oC = 2.3 kPa 100.0 kPa 2.3 kPa = 97.7 kPa
@STP what would the volume of the gas be? Which law would we have to use? Combined Law
P1 = 97.7 kPa V1 = 52.5 mL T1 = 20oC + 273K = 293K P2 = 101.3 kPa V2 = ? T2 = 273 K ( )( K 293 V2 = 47.2 mL ) ( ) 97 7 . 52 5 . 101 3 . kPa mL kPa V = 2 273 K
The spontaneous spreading of particles The rate of diffusion depends on the velocities and masses of the molecules Effusion from a small hole in a container Effusion the process by which a gas escapes Lighter gases ALWAYS than heavier molecules ALWAYS diffuse/effuse faster
The relative rates at which two gases, at the same temperature and pressure, will diffuse, vary inversely as the square root of the molecular mass of the gases. m v v **Always consider gas 1 the lighter gas = 1 2 m 2 1
Compute the relative rates of diffusion of helium and argon. go to the periodic table for molar mass of He and Ar
v m Mass He = 4 g/mol Mass Ar = 40 g/mol = 1 2 v m 2 1 40 v = = = 10 . 3 16 1 4 v 2 So, helium diffuses 3x s faster than argon. . 3 16 v = = . 3 16 1 1 v 2
Compare the rates of diffusion of O2 and N2. 32 v m = = = . 1 = . 1 14 07 1 2 28 v m 2 1 Since the lighter gas always diffuses faster, N2diffuses 1.07x s faster than O2
Compare the rates of diffusion of sulfur trioxide and nitrogen monoxide. 80 1 . v m = = = . 1 = . 2 67 63 1 2 30 v m 2 1 NO diffuses 1.63x sfaster than SO3
Gas #1 weighs 42.0 g/mol and diffuses at a rate of 5.65 m/s through an opening in a jar. Gas #2 weighs 252.0 g/mol. At what rate would it pass through the same opening? v m . 5 65 v 252 0 . = 1 2 = v m 42 0 . 2 1 2 . 5 65 v = v2 = 2.31 m/s . 2 45 2
