Ideal gas law, Charles' Law, Boyles' Law, Avogadro's Law, Dalton's law of partial pressures, the kinetic molecular theory of gases, gas diffusion and effusion

1. Gases
Jupiter 
Primarily made of
 airbag
hydrogen, a quarter of
A chemical reaction its mass is from Helium.
produces N2 gas to fill an
airbag, this happenes in
0.04 seconds, much faster
than the blink of an eye
(about 0.2 seconds)

2. Elemental Gases
Elements that exist as gases at 250C and 1 atmosphere
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3. Some Substances Found as Gases at 1 atm and 25oC
Elements Compounds
H2 (molecular hydrogen) HF (hydrogen fluoride)
N2 (molecular nitrogen) HCl (hydrogen chloride)
O2 (molecular oxygen) HBr (hydrogen bromide)
O3 (ozone) HI (hydrogen iodide)
F2 (molecular fluorine) CO (carbon monoxide)
Cl2 (molecular chlorine) CO2 (carbon dioxide)
He (helium) NH3 (ammonia)
Ne (neon) NO (nitric oxide)
Ar (argon) NO2 (nitrogen dioxide)
Kr (krypton) N2O (nitrous oxide)
Xe (xenon) SO2 (sulfur dioxide)
Rn (radon) H2S (hydrogen sulfide)
*The boiling point of HCN is 26oC, but it is HCN (hydrogen cyanide)* gas at
close enough to qualify as a
ordinary atmospheric conditions.
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4. Physical Characteristics of Gases
• Gases assume the volume and shape of
their containers.
• Gases are the most compressible state of
matter.
• Gases will mix evenly and
completely when confined to the
same container.
• Gases have much lower
densities than liquids and solids.
NO2 gas 
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5. Pressure
Force
Pressure = Area
(force = mass x acceleration)
Gravitational acceleration on Earth = 9.8 ms-2
What is 1 atmosphere? (atm)
Pascal (Pa) 1.01325 ×105
N/m2 1.01325 ×105
bar (bar) 1.01325
Torr (Torr) 760
mmHg 760
Pounds per
14.69595
square inch (psi) Barometer
Making a barometer:
http://www.youtube.com/watch?v=GgBE8_SyQCU
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6. 1 cm 1 cm
What is the mass
of a 1cm x 1cm air
column from sea
level to top of
atmosphere?
Cruising Jet
0.2 atm
(12 000m)
Everest (8840m) 0.33 atm
ANSWER = 1 kg
Sea level 1 atm
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7. The Gas Laws
• Relate the temperature, pressure and volume
of an ideal gas.
– Boyle’s law: pressure is inversely proportional to
volume at constant temperature
– Charles’ law: volume is directly proportional to
temperature at constant pressure
– Avogadro’s law: volume is directly proportional
to number of moles of gas present at constant
temperature and pressure
• These three laws are summarised in the ideal
gas equation: pV = nRT.
R = 0.082057 L • atm / (mol • K)
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8. Proportionality
• Proportionality: if two variables have a ratio that is
constant, they are said to be proportional.
• Put another way, one variable is a constant multiple
of the other.
• Direct Proportionality
– y = kx (where k is a non zero constant)
– eg, the circumference of a circle is proportional to its
diameter, constant is equal to π. (c = π d)
• Inverse Proportionality
– y = k x 1/x
– eg, the volume of gas is inversely proportional to the
pressure exerted, constant is equal to nRT. (PV = nRT)
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9. Apparatus for Studying the Relationship Between
Pressure and Volume of a Gas
a) Pressure b) Add more c) Add more
exerted on gas is mercury – an mercury again –
same as increase in another increase
atmospheric pressure in pressure
pressure exerted on exerted on gas.,
gas, volume volume
decreases decreases
As P (h) increases V decreases
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10. Boyle’s Law
P α 1/V Conditions:
P x V = constant Constant temperature
Constant amount of gas
P1 x V1 = P2 x V2
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11. Boyle’s Law
A sample of chlorine gas occupies a volume of 946 mL at a
pressure of 726 mmHg. What is the pressure of the gas (in
mmHg) if the volume is reduced at constant temperature to 154
mL?
P x V = constant
P1 x V1 = P2 x V2
P1 = 726 mmHg P2 = ?
V1 = 946 mL V2 = 154 mL
P1 x V1 726 mmHg x 946 mL
P2 = = = 4460 mmHg
V2 154 mL
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12. Gas expanding and contracting
As T increases V increases
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13. Charles’ Law
Variation of gas volume with temperature at constant pressure.
VαT
V = constant x T
V1/T1 = V2 /T2
Temperature
must be in Kelvin
T (K) = t (0C) +
273.15
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14. Charles’ Law
A sample of carbon monoxide gas occupies 3.20 L at 125 0C.
At what temperature will the gas occupy a volume of 1.54 L if
the pressure remains constant?
V1 /T1 = V2 /T2
V1 = 3.20 L V2 = 1.54 L
T1 = 398.15 K T2 = ?
T1 = 125 (0C) + 273.15 (K) = 398.15 K
V2 x T1 1.54 L x 398.15 K
T2 = = = 192 K
V1 3.20 L
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15. Avogadro’s Law
V α number of moles (n) Conditions:
V = constant x n Constant temperature
Constant pressure
V1 / n1 = V2 / n2
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16. Avogadro’s Law
Ammonia burns in oxygen to form nitric oxide (NO) and water
vapor. How many volumes of NO are obtained from one volume
of ammonia at the same temperature and pressure?
4NH3 + 5O2 4NO + 6H2O
1 mole NH3 1 mole NO
At constant T and P
1 volume NH3 1 volume NO
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17. Ideal Gas Equation
Boyle’s law: V α 1 (at constant n and T)
P
Charles’ law: V α T (at constant n and P)
Avogadro’s law: V α n (at constant P and T)
nT
Vα
P
nT nT
V = constant x =R R is the gas constant
P P
PV = nRT
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18. Gases at STP
• The conditions 0 °C and 1 atm are called
standard temperature and pressure (STP).
• Experiments show that at STP, 1 mole of an
ideal gas occupies 22.414 L.
PV = nRT
PV (1 atm)(22.414L)
R= =
nT (1 mol)(273.15 K)
R = 0.082057 L • atm / (mol • K)
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19. Ideal Gas Equation
What is the volume (in litres) occupied by 49.8 g of HCl
at STP?
PV = nRT T = 0 0C = 273.15 K
nRT
V= P = 1 atm
P
1 mol HCl
n = 49.8 g x = 1.37 mol
36.45 g HCl
L•atm
1.37 mol x 0.0821 mol•K
x 273.15 K
V=
1 atm
V = 30.6 L
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20. Dimensional Analysis
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21. Ideal Gas Equation
Argon is an inert gas used in lightbulbs to retard the vaporization
of the filament. A certain lightbulb containing argon at 1.20 atm
and 18 0C is heated to 85 0C at constant volume. What is the
final pressure of argon in the lightbulb (in atm)?
PV = nRT n, V and R are constant
nR
= P = constant P1 = 1.20 atm P2 = ?
V T
T1 = 291 K T2 = 358 K
P1 P2
=
T1 T2
T2
P2 = P1 x = 1.20 atm x 358 K = 1.48 atm
T1 291 K
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22. Density and Molar Mass calculations
Density (d) Calculations
m = PM m is the mass of the gas in g
d=
V RT M is the molar mass of the gas
Molar Mass (M ) of a Gaseous Substance
dRT
M= d is the density of the gas in g/L
P
Practice the derivations of these equations
from PV = nRT yourself!
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23. Density and Molar Mass calculations
A 2.10-L vessel contains 4.65 g of a gas at 1.00 atm
and 27.0 0C. What is the molar mass of the gas?
dRT m = 4.65 g = 2.21 g
M= d=
P V 2.10 L L
g L•atm
2.21 L x 0.0821 mol•K
x 300.15 K
M=
1 atm
M = 54.6 g/mol
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24. Gas Stoichiometry
What is the volume of CO2 produced at 37 0C and 1.00 atm
when 5.60 g of glucose are used up in the reaction:
C6H12O6 (s) + 6O2 (g) 6CO2 (g) + 6H2O (l)
g C6H12O6 mol C6H12O6 mol CO2 V CO2
5.60 g C6H12O6
= 0.031 mol C6H12O6 x 6 mol = 0.187 mol CO2
180 gmol -1
L•atm
0.187 mol x 0.0821 x 310.15 K
nRT mol•K
V= = = 4.76 L
P 1.00 atm
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25. Dalton’s Law of Partial Pressures
V and T
are
constant
P1 P2 Ptotal = P1 + P2
P1
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26. Dalton’s Law of Partial Pressures
• Daltons Law: the total pressure of a mixture
of gases or vapours is equal to the sum of the
partial pressures of its components.
• ie, the sum of the pressures that each
component would exert if it were present
alone and occupied the same volume as the
mixture of gases.
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27. Dalton’s Law of Partial Pressures
Consider a case in which two gases, A and B, are in a
container of volume V.
nART nA is the number of moles of A
PA =
V
nBRT nB is the number of moles of B
PB =
V
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28. Dalton’s Law of Partial Pressures
nA nB
PT = PA + PB XA = XB =
nA + nB nA + nB
number of moles of gas G
n
mole fraction (XG) = G
nT
TOTAL number of moles
of all gases in the vessel
PA = XA PT PB = XB PT PG = XG PT
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29. Dalton’s Law of Partial Pressures
A sample of natural gas contains 8.24 moles of CH4, 0.421
moles of C2H6, and 0.116 moles of C3H8. If the total pressure
of the gases is 1.37 atm, what is the partial pressure of
propane (C3H8)?
Pi = Xi PT PT = 1.37 atm
0.116
Xpropane = = 0.0132
8.24 + 0.421 + 0.116
Ppropane = 0.0132 x 1.37 atm = 0.0181 atm
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30. Kinetic Molecular Theory of Gases
• Kinetic Molecular Theory of Gases
explains what is happening to gases at the
molecular level.
• We know that gas will expand on heating
(Charles’ Law) but WHY?
• The physical properties of gases can be
explained in terms of the motion of individual
molecules. This molecular movement is a
form of energy.
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31. Kinetic Molecular Theory of Gases
1. A gas is composed of molecules that are separated from
each other by distances far greater than their own
dimensions. The molecules can be considered to be points;
that is, they possess mass but have negligible volume.
2. Gas molecules are in constant motion in random directions,
and they frequently collide with one another. Collisions
among molecules are perfectly elastic.
3. Gas molecules exert neither attractive nor repulsive forces
on one another.
4. The average kinetic energy of the molecules is proportional
to the temperature of the gas in kelvins. Any two gases at
the same temperature will have the same average kinetic
energy m = mass of molecule
KE = ½ mu2 u = molecule speed
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32. Kinetic Molecular Theory of Gases
• According to the kinetic molecular theory, gas
pressure is the result of collisions between
molecules and the walls of their container.
• The absolute temperature of a gas is a
measure of the average kinetic energy of the
molecules.
• The higher the temperature, the more
energetic the molecules.
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33. Kinetic theory of gases and …
• Compressibility of Gases
• Boyle’s Law
*number density =
P α collision rate with wall number of molecules per
unit volume
Collision rate α number density*
Number density α 1/V
P α 1/V
• Charles’ Law
P α collision rate with wall
Collision rate α average kinetic energy of gas molecules
Average kinetic energy α T
PαT
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34. Kinetic theory of gases and …
• Avogadro’s Law
P α collision rate with wall
Collision rate α number density
Number density α n
Pαn
• Dalton’s Law of Partial Pressures
Molecules do not attract or repel one another
P exerted by one type of molecule is unaffected by the
presence of another gas
Ptotal = ΣPG
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35. Distribution of Molecular Speed
The distribution of speeds for nitrogen gas molecules at
three different temperatures
The higher the
temperature of the
gas, the faster the
molecules of the
gas move.
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36. Distribution of Molecular Speed
The distribution of speeds of three different gases at
the same temperature
The heavier the
gas, the more
slowly its
molecules move.
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37. Root-Mean-Square Speed
• How fast does a molecule move, on average
at any temperature, T?
• The root-mean-square (rms) speed (urms) is
an average molecular speed
urms = √ 3RT
M M = molar mass
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38. Gas Diffusion
• Gas diffusion is the gradual mixing of molecules of
one gas with molecules of another by virtue of their
kinetic properties.
The path traveled
by a single gas
molecule. Each
change in direction
is a collision with
another molecule
• A lighter gas will diffuse through a certain space
more quickly than will a heavier gas
– (Since the rms of a light gas is greater than that of a
heavier gas)
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39. Gas Diffusion
√
r1 Graham’s Law of
= M2 diffusion
r2 M1 (r1 and r2 are the diffusion
rates of the gases)
NH4Cl
Since NH3 is lighter
than HCl, it diffuses
faster, so solid
NH4Cl first appears
nearer to the HCl
bottle on the right
NH3 HCl
17 g/mol 36 g/mol
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40. Gas Effusion
• Gas effusion is the process by which a gas under
pressure escapes from one compartment of a
container to another by passing through a small
opening.
• Effusion is different from diffusion in nature, but the
rate of effusion of a gas follows the same form as
Graham’s law of diffusion.
√
r1 t2 M2
= =
r2 t1 M1
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41. Gas Effusion
Nickel forms a gaseous compound of the formula Ni(CO)x
What is the value of x given that under the same conditions
methane (CH4) effuses 3.3 times faster than the compound?
r1 2
r1 = 3.3 x r2 M2 = (r )
2
x M1 = (3.3)2 x 16 = 174.2
M1 = 16 g/mol 58.7 + x • 28 = 174.2 x = 4.1 ~ 4
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42. Credits
• McGraw Hill Publishing
• Wikipedia Creative Commons Images
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