EXAM 1 CHEM 202

Lecture : 1/9/24

* *
phases : solid : Liquid ,
gas entropy is referred to as positive or negative ,
not


*
intermolecular forces hold molecules together , & endothermic/exothermic .
*
entropy keeps molecules apart. enthalpy from solid >
-
liquid will be less than

is needed to transform
-entropy will favor
gas phase ,
therefore liquid a
gas because more energy

intermolecular forces a liquid to a gas than a solid to liquid .
will favor condensed phases

such as liquid a solid . *
Vaporization/Condensation
*
Molecules liquid have some freedom of motion
entropy- degree of randomness , degree of disorder in the


-options for energy; how much energy
is through movement a interactions they transfer

distributed in the system .
the energy.

it can
high enough overcome
-




for location ; where If the is
options energy
-


the molecule is

located ; larger volumes allow more options . Molecular forces ; the molecules closer to the surface

Orientation direction :
of the molecule . with the energy high enough can escape to the

motion how fast & What direction
:
the
gas phase .
*
avaporation vaporization from the surface.
:
molecules are moving
* In container , molecules can escape to the
High entropy
an
restrictions -
-

=
more options , less open

low : less options more restrictions. gas phase
until there is no liquid left.
entropy ,




rate of vaporizations rate of condensation
thermodynamic function = *
*
Entropy is a
represented

by the letter"S". -

in a closed container , at first rate of vaporization >




-solid :
entropy low ; liquid-moderate ; gas-high rate of condensation . At the point of balance (equilibrione
low entropy :
high intermolecular forces the rate of vaporization =
rate of condensation

*
SH =
enthalpy for :
the phase change involves
&
Equilibrium :
Kinetic definition -

the rates (speeds) of the

the
energy of making & breaking the intermolecular
opposing processes are
=



forces
enthalpy & entropy
.
-from thermodynamic definition :




-solid-liquid fusion (melting) :

AHersa of the System are in balance.


endothermic =
pos .

entropy.
*
Equilibrium Vapor Pressure (EVP)
of the gas at equilibrium with its liquid
liquid-solid freezing -pressure
-



AH
.
: :
freez
exothermic =

neg. entropy
-
p =
Y + RXT


as increases , GVP increases
entropy
-


as well
-




liquid-gas :
vaporization Alt vapa
:




endothermic =
pos entropy
.




-gas-liquid :
condensation : DH cond

exothermic
=
neg .

entropy

-solid ->
gas Sublimation
: :

AHsib
endothermic
=
pos entropy
.




- gas -
solid :
deposition Aldep :




exothermic =
neg. entropy

, lecture : 1/11/24
* DIAGRAM :
vaporization/condensation :




diethyl ether methanol water (H20)

(e)


De
IFS :
weakest moderate Strongest
>
- equilibrium 8

Al vap : lowest moderate highest

4VP :
highest moderate lowest

upp : lowest moderate highest

equilibrium temperature in 'C *
Boiling :




from the surface.
evaporation Vaporization
:
Relative Humidity
-



* :



boiling : EVP7 atmosphere pressure
PLA2O
RH-Actual
-
.




x10 %
-

no boiling :
EvPs atmosphere pressure .




* *
How saturated with moisture can air be? When tempreature increases , GVP increases .




not

unsaturated Tequilibrium boiling .
-



RH 100 %; actual PLEVP eventually GVP
: -
=
atmosphere pressure -
saturated : RH *
Boiling point (bp) temprature when EVP
-



EvP
:
100 %; actual p -
equilibrium
=
= =
external
not at
supersaturated : RH >100 %; EvP +equilibrium pressure.
->
boiling point (nbp)
-


actual p > normal =
1 atm .


* * In
saturated raining an
open container >
- Molecules can escape to the gas
*
supersaturated : before rain .

phase until there is no solids left.

*
Consequences of Relative Humidity in closed container- > At first sublimation
-

:
,




-drying occurs faster at RH. deposition , until equilibrium then sublimation =




-general well being
-
Need As because humidity deposition. * sublimation

-in winter the air indoors is "drier" than a
Sublimation v .
deposition. point the point
:
in


outdoors . which solids under




Sup
dewpoint logarthmic go sublimationat
-




>
-
&
EvP-actual p equilibrium
the temperature which given
-
in .


pressure
* similar to bp .
When RH =
100% % condensation begins.
*
when avp =
actual p :
that temp: the tempreature .




dewpoint and condensation will begin .
&
Fusion/Freezing :
solids liquids . gas phase not


* What EvP has to do with intermolecular forces :
involved so :

normal more typical less typical
-weak intermolecular forces for
less
energy needed
:




I I
P




M
Molecules to escape to the -
more P (s) (e) p
gas phase
AHap
=

Molecules can escape to gas phase
- lower

EVP .
more molecules in gas phase higher
=




intermolecular forces Temp Temp Temp
-higher
:
needed
more
energy
for to escape to
-




molecules most substances Water Hzo .
gas phase
less
-




DH
Vap temp4n ↑
-

as temp
Molecules can escape to
gas phase higher as .
.


less Molecules in gas phase = lower avp . P increases ↑ decreases.