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GEN CHEM 2
Phase Changes
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Cards (9)
Phase changes
Solid-liquid, liquid-vapor, and solid-vapor
Liquid-vapor equilibrium
1. Overcome intermolecular forces by adding
energy
enough to
vaporize
the
liquid
(
molar
heat
of
vaporization
)
2. At equilibrium, the
rate
of
evaporation
is
equal
to the
rate
of
condensation
Molar
heat
of
vaporization
Energy
required
to
vaporize
1
mole
of a
liquid
Intermolecular forces vary from one substance to another, so the
molar
heat
of
vaporization
is
not
the
same
for
all
substances
Liquids with
strong
intermolecular
forces
have
high
molar
heats
of
vaporization
Condensation
Reverse process of vaporization, requires heat to be released, has a heat change (∆Hcond) with negative sign
The values of
∆Hcond
have the same
numeric
value
of ∆Hvap
Liquid-solid equilibrium
1.
Molar
heat
of
fusion
(∆Hfus) is the
amount
of
energy
required to
melt
1
mole
of a
solid
2.
Molar
heat
of
freezing
(∆Hfreeze) is the
amount
of
heat
released
to
freeze
a
liquid
,
equal
in
magnitude
but
opposite
in
sign
to ∆Hfus
Solid-vapor equilibrium
1.
Sublimation
is the process of
converting
solid
to
gas
,
deposition
is the
reverse
process
2.
Molar
heat
of
sublimation
(∆Hsub) is the
energy
required to
sublime
1
mole
of
a
solid
, it is the
sum
of the
molar
heats
of
vaporization
and
fusion
