Gibb's free energy

1
Chapter 16, so beautiful and its mine 1st Law
of Thermodynamics the energy in the universe is
_________ (it cannot be created nor destroyed,
but can be converted from one form to
another). Sec16.1 Spontaneous Processes and
Entropy 1. A reaction which can occur with no
outside intervention is ______________. (this
says nothing of the rate of the reaction-a
diamond will spontaneously change to graphite
but does so very slowly) see examples on pg.
785 2. The spontaneity of a reaction deals with
______ (enthalpy) and ______ (entropy). Entropy
is the measure of randomness or disorder. The
temperature of the system also plays a role. 3.
Exothermic systems (?H ___) tend to proceed
spontaneously as well as systems tend
toward greater disorder (?S ___) . Note it is
not required that ?H be and ?S be for a
system to proceed spontaneously. An example
Ice melting above 0oC is an endothermic process
(?H ) but a liquid is much more random than a
solid (?S ). However, it will freeze below 00
C. Sgas gtgtSliquidgtSsolid Entropy is a
thermodynamic function that describes the numbers
of positions available to a system in a given
state. See Table 16.1 pg. 787
constant
spontaneous
?H
?S
-

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Sample Exercise 16.1-2 pg. 789-790 Sec 16.2
Entropy and the 2nd Law of Thermodynamics For
any spontaneous process there is an _____________
in the entropy of the universe. (so we see that
entropy of the universe is not conserved) 1. The
entropy of the universe can be broken into 2
parts a. the entropy of the system b. the
entropy of the surroundings ?Suniv ?Ssys
?Ssurr 2. If ?Suniv is ____, then the process
will proceed in the direction written. (if
then it will proceed in the opposite direction as
written) (if 0 then it has no tendency to proceed
in either direction) Sample Exercise 16.3 pg.
790 Sec 16.3 The Effect of Temperature on
Spontaneity Consider H2O (l) ? H2O (g) (H2O is
our system and everything else is the
surroundings) What happens to the entropy of
water in this process? Consider that 1 mol of
water occupies a volume of ____ ml at 100oC while
steam occupies a volume of ____ L at 100oC.
Since there are many more positions available
for each steam molecule the system is proceeding
towards more randomness (?Ssys )

increase

18
31

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What about the entropy of the surroundings? Here,
heat is taken in from the surroundings by the
system. This decrease in temperature experienced
by the surroundings will ___________ the motion
of the surrounding particles thereby making
?Ssurr 1. The sign of ?Ssurr depends upon the
direction of the _________ flow. 2. The
magnitude of ?Ssurr depends upon the
_______________. ?Ssurr - ?H / T See table
16.3 pg. 794 As T decreases, ?Ssurr gets more
(so ?Suniv gets more negative) The system will
have less chance of proceeding (?Suniv must be
positive and is equal to ?Ssurr ?Ssys) Sample
Exercise 16.4 ?Ssurr - ?H / T ?Ssurr - ?H
/ T ?Ssurr -(-125 kJ / 298 K) ?Ssurr -(778
kJ / 298K) ?Ssurr 419 kJ /K ?Ssurr
-2.61.103 kJ/K Next time we will examine free
energy ?G ?H - T?Ssys (for a spontaneous
process to occur, ?G must be negative) See table
16.4 pg. 796
decrease
-
heat
temperature
Homework pg. 818 -819 s 7-9 15-17 19 (the
greater the volume, the greater the positional
entropy) 20 21
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(No Transcript)
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• Gibbs Free Energy
• (be sure to give quality responses on you
  homework especially letters B and G no Jive
  Talkin)
• Sec 16.4 Free Energy
• Last lesson we utilized ?Suniv to determine
  reaction spontaneity
• (?Suniv has to be ___ for a process to be
  spontaneous).
• 2. This lesson will explore spontaneity
  through the use of Gibbs free energy.
• (?G has to be ___ for a process to be
  spontaneous). See table 16.5 pg. 797
• ?G ?H - T?S ?Suniv - ?G / T
• 3. At an equilibrium condition ?Suniv and ?G
  ____
• (note normal melting and boiling are equilbrium
  conditions)
• Sample 16.5 pg. 797
• To be at equilibrium ?Go 0
• ?Go ?Ho - T?So
• 0 ?Ho - T?So
• T ?Ho / ?So
• T (3.10.104 J / mol) / (93.0 J /Kmol)
• T 333 K at equilibrium
• Since ?So is , the -T ?So is -. Therefore any
  T greater than 333 K will yield a - ?Go.
• So the system is spontaneous at T gt 333K

The energy available for work from a process

-
0
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• Sec 16.5 Entropy Changes in Chemical Reactions
• As discussed earlier, the entropy change of the
  surroundings is determined by the
• direction the _______ flow
• 2. The system entropy merely depends upon
  the positional entropy or the _________ of
  arrangements or positions available. For a given
  system
• Haber Process N2 (g) 3 H2 (g) ? 2 NH3 (g)
• if there are greater numbers of gaseous reactant
  molecules
• than product molecule ?Ssys will be ___
• (?Ssys is ___ if there are more gaseous product
  molecules than reactant molecules).
• Sample Exercise 16.6 pg. 799
• The 3rd Law of Thermodynamics (the entropy of a
  perfect crystal at __ K is 0).
• If the temperature of the crystal increases at
  all, there will be vibrations within the molecule
  giving it some randomness. Fig. 16.5 pg. 799
• 3. The greater the complexity of a molecule
  (more atoms means more complexity), the
  ___________ the entropy of the molecule.
• 4. Entropy is a state function (independent of
  ________________) and may be calculated as
  follows
• ?So SnSo products SnSo reactants use table
  in back of book for So values

heat
numbers
-

0
greater
pathway
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Sample Exercises 16.7 ?So
SnSoproducts SnSoreactants 16.8 ?So
SnSoproducts SnSoreactants Sec 16.6 Free
Energy and Chemical Reactions ?Go measures
whether a system will proceed spontaneously or
not but says nothing of the _____ of the
reaction. ?Go may be calculated as follows ?Go
Sn?Goproducts Sn?Goreactants ?Go ?Ho -
T?So ?Ho Sn?Hoproducts Sn?Horeactants ?So
SnSoproducts SnSoreactants Sample Exercises
16.9 ?Ho Sn?Hoproducts Sn?Horeactants ?So
SnSoproducts SnSoreactants ?Go ?Ho -
T?So 16.10

rate
16.11 ?Go Sn?Goproducts
Sn?Goreactants 16.12 ?Go
Sn?Goproducts Sn?Goreactants
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Homework Day 1 pg. 818-820 s 10 23a,b
24a 25 27 29 31 32 33 35 39 Day 2 pg.
818-820 s 11 23c,d 24b,c 26 28 30 34b
36 40 41a,b Answers to 16.1-16.3 7, 9,
11,15,17,21 (see back of book) 8a. an increase in
volume will increase the positional entropy b.
The entropy of position doesnt change because
the volume is constant, there are still the same
numbers of positions available to each particle
despite its speed. c. an increase in pressure
will decrease the volume and thus decrease the
positional entropy. 16. c and d are spontaneous
(especially if its my kitchen) 20. a,b,d,f show
an increase in entropy
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Sixteen Candles (or at the very least Chapters
that have blown out after today - 1) Sec 16.7 The
Dependence of Free Energy on Pressure 1. As a
spontaneous reaction proceeds, the free energy of
the system changes (the free energy approaches __
until a state of equilibrium is reached). 2.
Recall in the previous chapters an analysis of
which direction a process would proceed was
determined by an analysis of ___. So free energy
(?G) at conditions other than standard
conditions, depends upon Q. (for gases, Q depends
upon the __________ of the gases). ?G ?Go RT
ln Q Sample Exercise 16.13 pg. 808

0
Q
pressure
?G ?Go RT ln Q ?G -2.9.104 J /mol rx
(8.3145 J /molK)(298 K) ln (0.02222) ?G
-29.103 J /mol rx 9.432 .103 J /mol rx ?G
-38 .103 J /mol or 3.8.104 J/mol or -38
kJ/mol
Q 1 / ((5.0 atm)(3.0 atm)2) Q 0.02222

?Go (1mol(-166 kJ/mol))
(1 mol (-137 kJ/mol)) ?Go -29
kJ or -2.9.104 J (forming 1 mol of product)
?Go -2.9.104 J /mol rxn

• The meaning of ?G for a Chemical Reaction
• Any process has a tendency to reach its
  _____________ energy state. When ?G
• is __, the system will proceed spontaneously.
  Spontaneously does not mean that the
• reaction will go to completion.
• At completion Q would be __ (for one of the
  reactants would be 0) and so ?G would
• be positive. A condition exists before the
  system goes to completion for a spontaneous
• process that is referred to as ___________________
  . See fig. 16.7-16.8 pg. 809-810

lowest
-
8
equilibrium
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Sec 16.8 Free Energy and Equilibrium See fig.
16.9 pg. 810 to observe the location for an
equilibrium condition. At equilibrium ?G ___ ,
so ?Go -RT ln K. See table 16.6 pg. 812 Sample
Exercises 16.14 pg. 812-813. Sample Exercise
16.15 pg. 813-4
0
?G ?Go RT ln Q a. ?G 0 so no
tendency either direction b. ?G -33.3
kJ/mol So a tendency to the right
?Go -RTlnK K e (?Go / RT) K e -
(-1,490,000 J / 8.3145 J/molK(298K) K
e601 (a very large K)
The Temperature Dependence of K So far we have
seen that ?Go ?Ho -T?So and ?Go -RT ln
K ?Ho -T?So -RT ln K Rearranged this turns into
the following ln K -(?Ho/R)(1/T) ?So/R
y
m x b A plot of ln K
vs 1/T will yield a straight line of slope
________ and y-intercept ________. Sec 16.9 Free
Energy and Work 1. Chemical processes can do
_______ if they proceed spontaneously to any
appreciable extent. 2. The maximum amount of
work that can be obtained is equal to ___ for a
process at constant T and P (however there are
always losses in energy so this maximum amount
won't be obtained). wmax ?G If ?G is __ then
work can be obtained by the process with no input
of energy, (if __ then work must be input to have
the process proceed spontaneously). Read pg.
814-15.

-?Ho/R
?So/R
work
?G
-