8. gases

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Review

Table A: STP
1 atm = 101.3 kPa = 760.0 mm Hg
Vapor
= gas that is usually a liquid
Vapor Pressure: when a gas exerts pressure on
its surroundings.
SLG (endothermic)
 SL melting
LG boiling, evaporation
 GLS (exothermic)
GL condensation
LG freezing

SG sublimation
GS deposition
 Temp = average kinetic energy
TABLE H:
Boiling Point: vapor pressure = atm. pressure
Boyle’s Law

At constant temperature, volume and
pressure are inversely proportional.
P1V1 = P2V2
Charles’ Law

At constant pressure, volume and temperature
are directly related (temp. must be in kelvin)
V1 = V2
T1 = T2
Combined Gas Law
Used to solve for either pressure, volume, or
temperature when no variable is constant.
 Pressure = atm, kPa,
 Volume = ml, L, cm3
 Temperature = Kelvin
 Remember that STP = numerical values!!!!
P1V1 = P2V2
T1
T2

Avogadro’s Law: Equal volumes of different
gases at the same temperature and pressure
contain an equal number of molecules.

6.02x1023 molecules = 22.4 L
Graham’s Law: Relates the rate of diffusion of
gases to their molar masses; the greater the
mass, the slower it diffuses, the smaller the
mass, the faster it diffuses.
Kinetic Molecular Theory: used to describe the
behavior of an “ideal gas”.
1.
A gas is composed of particles that are in continuous
random motion.
2.
When gas molecules collide with each other or with
the walls of the container, there is a transfer of
energy between colliding particles; the total energy
remains constant.
3.
The volume of gas particles is negligible in
comparison with the volume of space they are in.
There is a lot of space between the particles.
4.
Gas particles are considered as having no force of
attraction for each other.
“Real gases” deviate from the “ideal gas laws”
 There are deviations from the four key points made in
the KMT.
 Point 3 Deviation: The volume of gas particles is
significant. Gas particles do have some volume.
 Point 4 Deviation: Gas particles do have a force of
attraction.

IDEAL GASES:
Exist under conditions of low pressure & high temperature.
REAL GASES:
Exist under conditions of high pressure & low temperature.

HYDROGEN and HELIUM are two “real gases” that behave the
most like IDEAL gases.
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