8.5-10.1 exam/final Flashcards
gas diffursion
high to low concentration
mean free path
avg. distance travled by a molecule between collisions
Mean free path at sea lvl
60 nm
mean free path at 100 km altitude
10 cm
mean free path increase with
decreasing pressure
gas effusion
transfer of gaseous atoms or molecule from a container to a vaccum through very small openings
At a given temperature, lighter particles travel
faster then heavier particles
Kinetic Molecular Theory: Postulates
1-Gas molecules are in
continuous motion, travelling in straight lines
and changing direction only when they collide with other molecules
or with the walls of the container
Kinetic Molecular Theory: Postulates
2-Volume occupied by gas particles is
SMALL compared to the volume
of the container itself. The molecules composing the gas are
negligibly small compared to the distances between them.
Kinetic Molecular Theory: Postulates
3-The pressure exerted by a gas in a container results from
collisions
between the gas molecules and the container walls
Kinetic Molecular Theory: Postulates
4:Gas molecules exert
no attractive or repulsive forces on each other or
the container walls; therefore, their collisions are elastic (do not
involve a loss of energy).
Kinetic Molecular Theory: Postulates
5:The average kinetic energy of the gas molecules is
proportional to the
temperature (in Kelvin).
AMONTONS LAW
temp increased volume constand
Gases behave ideally when: The volume of gas particles is
small compared to
the space between them.
Gases behave ideally when:The intermolecular forces between
gas particles
are not significant.
ideal behavior occurs: At High
pressure
Actual Volume of gas atoms
greater than predicted
Non-ideal behavior occurs: at low
temps
actual pressure is less than predicted
intermolecualr
Attractive forces that exist
between all molecules and
atoms
Strength of the forces
determines the state of matter
Intermolecular forces are strong
enough to control physical
properties such as boiling and
melting points, vapor pressures,
and viscosities
intramolecular
within’
intramolecualr foreces keep a molecule intact
The STRONGEST intermolecular force, however,
is still weaker than
bonding forces!
Dispersion Forces
London dispersion forces, or
dispersion forces, are attractions
between an instantaneous dipole
and an induced dipole.
These forces are present in all molecules, whether they are polar
or nonpolar.
polarizability
polarizability
The tendency of an electron cloud to distort in this way is called
polarizability.
Factors Affecting
Dispersion Forces
The strength of
dispersion forces tends
to increase with
increased molecular
weight.
* Larger atoms have larger
electron clouds that are
easier to polarize
-Therefore the greater
strength of dispersion
forces results in
increased boiling
points.
* The shape of the molecule
also affects the strength of
dispersion forces: long,
skinny molecules (like n-
pentane) tend to have
stronger dispersion forces
than short, compact ones (like
neopentane).
* This is due to the increased
surface area.
Dipole-dipole Forces
- Molecules that have permanent dipoles are attracted to each other.
- The positive end of one is attracted to the negative end of the other, and vice
versa. - These forces are only important when the molecules are close to each other.
The more polar the molecule, the
higher its boiling point!
This is due to the increased strength of the dipole-dipole forces
