Gases
Nature of Gases
1 – gases have mass (low density)
2 – particles glide past one another (flow) - fluid
3 – easily compressed
4 – fill containers completely
5 – diffuse easily*
6 – gases exert pressure
7 – pressure depends on temperature
*diffusion – spontaneous mixing of the particles of
two substances
-movement of one substance through another
Kinetic Theory

1.
2.
3.
4.
5.
Explains properties of gases (ideal gas)
Gas particles are relatively far apart
Collisions are elastic
Gas particles are in constant, fast, random
motion (Brownian motion)
Gas particles do not stick, like billiard balls
Kinetic energy depends on temperature
Pressure
force per unit area
 pressure = force/area
 SI unit of force – newton (N)
 STP – standard temperature and pressure

◦ 1 atm and 0°C
Units of Pressure
Unit of Pressure
Standard
atmosphere
1 atm
millimeters of mercury
760 mm Hg
torr
760 torr
inches mercury
29.9 in
pounds per square inch
14.7 psi
bar
1 bar = 100 kPa
kilopascals
101.3 kPa
Conversions:
How many atmospheres are equal to 10 psi?
If a pressure is equal to 101.3 kPa, what is the pressure in mm Hg?
Types of Pressure

atmospheric pressure
◦ pressure exerted by the air pressing down on
earths surface
◦ measured by barometer and manometer

gas pressure
◦ gas particles colliding with the sides of the
container it is in
Barometer

an instrument that measures atmospheric
pressure
Manometer

an instrument that measures pressure of
a gas in a container vacuum
THE GAS LAWS
Avogadro’s Law

equal volumes of gases at the same
temperature and pressure have equal
numbers of particles

1 mole of any gas = 22.4 L
Dalton’s Law of Partial Pressure

the sum of the partial pressures of each
gas in a mixture equals the total pressure
of the mixture
 Pt
= P1 + P2 + P3 ….
Classwork/Homework

In your books (Modern Chemistry)
◦ pg 312
 Section Review 1-4
 pg 327 16-19
 Pg 329 39

Skim Chapter 10 Section 3 for tomorrow
Boyle’s Law
P1V1 = P2V2
temperature remains constant
 pressure and volume are inversely related

◦ P – pressure
◦ V – volume
◦ T - temperature
Practice Problems
At a constant temperature, the volume of
a gas is 30.2 L and the pressure is 356
torr. If the pressure has increased to 700.
torr, what is the new volume of the gas?
 At STP, carbon dioxide fills a 6.5 L
container. If the container is compressed
to a volume of 3.2 L, what pressure (in
kPa) will the gas exert?

Charles’ Law
V1
T1
= V2
T2
K-273 = C
pressure remains constant
 volume is directly related to temperature
 temperature must be in K

Practice Problems


A balloon filled with helium at STP has a
volume of 4.7 L. If pressure is held constant
and the temperature is raised 10 degrees
Celsius, what is the new volume of the
balloon?
A 500. mL container houses argon at 373 K.
If the container is compressed to a new
volume of 0.300 L, what will the
temperature of the gas be (assuming
pressure remains the same)
Gay-Lussac’s Law
P1
T1
= P2
T2
volume remains constant
 pressure is directly related to
temperature

Practice Problems


A container of gas with a temperature of
290 K has a pressure of 1.9 atm. This
container is pressurized so the new
temperature is 397 K. What is the new
pressure?
The volume of a fixed container is 4.03 L. It
is filled with neon gas at 46 degrees Celsius
and the gas exerts a pressure of 800 torr.
This container is heated to 84 degrees
celcius. What pressure does the gas exert?
Combined Gas Law
P1V1 = P2V2
T1
T2

No variable remains constant
Practice Problems
The volume of a gas at 30 degrees celcius is
8.54 L. The pressure is increased from 760
mm Hg to 943 mm Hg. If the temperature
increases 8 degrees celcius, what is the new
volume?
 A 2.7 L container filled with carbon
monoxide at 400 K has a pressure of 5.7
atm. If the container is compressed to a
volume of 1.0 L and a pressure of 6.0 atm,
how will the temperature change? What is
the new temperature?

Classwork/Homework

Please work in your books on the
practice sections of pg 315, 319, 320, 322

If you do not finish this in class, please
finish it for homework
Ideal Gas Law

PV = nRT
“piv nurt”
n - number of moles
 R - gas constant

◦ Values of R:
 0.0821
 62.4
 8.31
atm
mmHg
kPa
V in L
T in K
n in mol
Practice Problems
Exactly 1 mole of carbon dioxide is in a
4.0 L container at 283 K, what is the
pressure the gas exerts?
 2.4 moles of gas is exerting 760 torr on a
30.0 L container, what is the temperature
of the gas in Celsius?
 A gas is contained in 2.87 L container at
300 K. The pressure exerted is 220. kPa. If
the gas is CO2, what mass of the gas is in
the container?

Ideal Gas Law

Molar Mass
◦ MM = gRT/PV

Gas Density
◦ D= m/v
d = PMM/RT
◦ As temperature increases, volume increases
◦ As volume increases and mass remains the
same, density decreases
Practice Problems
6.00 g of He is contained in a box at STP,
what is the volume of the box?
 Calculate the density of a gas with a
molar mass of 132 g/mol at STP.
 Neon gas is contained in a 55 L container
at 297 K; if the neon exerts a pressure of
1000. torr, what is the mass of the gas?

HW

Pg 357
◦ 16-19 letter c only
◦ 20
◦ 21
Graham’s Law of Diffusion
v1 =
v2
d2
d1
v – rate of diffusion
d – density
m – molar mass
v1
v2
=
m2
m1
Practice Problems

Calculate the relative rates of diffusion of
O2 and H2
H subscript 1, O subscript 2

Answer: molecule 1 is 4 times molecule 2
◦ H2 is 4 times faster than O2/diffuses 4x faster
Practice Problems
If equal amounts of helium and argon are
placed in a porous container and allowed
to escape, which gas will escape faster and
how much faster?
 What is the molecular weight of a gas
which diffuses 1/50 as fast as hydrogen?
 How much faster does hydrogen escape
through a porous container than sulfur
dioxide?

Collecting a gas over water
 Patm
 PH20
= Pgas + PH 0
depends on temperature
2
Practice Problems
If we collected 310.0 mL of gas over water
at a pressure of 738 mmHg and a
temperature of 20.0°C, what is the partial
pressure in atm of H2(g) in the test tube?
 193 mL of O2 was collected over water on a
day when the atmospheric pressure was 762
mmHg. The temperature of the water was
23.0 o C. How many grams of oxygen were
collected?
