Chap15_Part1

Chap15_Part1 - Chemistry 102: General Descriptive Chemistry...

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Unformatted text preview: Chemistry 102: General Descriptive Chemistry II Brown, LeMay & Bursten Chemistry: The Central Science, 11th Edition Chapter 15: Chemical Equilibrium 1 Chapter 15 Homework Red concepts: 15.1, 15.4, 15.7 Red exercises: 15.9, 15.13, 15.15, 15.17, 15.19, 15.21, 15.23, 15.27, 15.29, 15.31, 15.33, 15.35, 15.37, 15.39, 15.41, 15.43, 15.49, 15.51, 15.53, 15.62, 15.68, 15.80, 15.83 2 1.
Will
the
reac-on
occur?
THERMODYNAMICS
 2.
How
fast
will
the
reac-on
occur?
CHEMCIAL
KINETICS
 3.
How
far
will
the
reac-on
proceed?
CHEMCIAL
EQUILIBRIUM
 3 Chemical Equilibrium Chemical
equilibrium
is
achieved
when:
 •  The
rates
of
the
forward
and
reverse
reac-ons
are
equal
and

 •  The
concentra-ons
of
the
reactants
and
products
remain
constant
 • 



At
equilibrium
there
is
no
net
change
in
the
concentra-ons
of
 




reactants
and
products.
 • 



Nonetheless,
individual
molecules
are
constantly
undergoing
changes.
 • 



Equilibrium
is
always
eventually
reached
in
a
closed
system.
 +
 →
 ←
 Equilibrium
looks
at
the
extent
of
a
chemical
reacDon.
 4 Chemical Equilibrium Physical
equilibrium
 (dynamical
Equilibrium)

 H2O
(l)
 H2O
(g)
 Chemical
equilibrium

 N2O4
(g)
 2NO2
(g)
 A
Tug‐of
war
game
between
2
equal
forces:
StaDc
Equilibrium
 Chemical
Equilibrium
occurs
when
opposing
reac-ons
proceeding
 with
equal
rates
 5 •  Consider
colorless
frozen
N2O4.

At
room
temperature,
it
 decomposes
to
brown
NO2:
 N2O4(g)
→
2NO2(g).
 •  At
some
-me,
the
color
stops
changing
and
we
have
a
mixture
of
 N2O4
and
NO2.
 •  Chemical
equilibrium
is
the
point
at
which
the
rate
of
the
forward
 reac-on
is
equal
to
the
rate
of
the
reverse
reac-on.

 At
that
point,
the
concentra-ons
of
all
species
are
constant.
 •  Using
the
collision
model:

 –  as
the
amount
of
NO2
builds
up,
there
is
a
chance
that
two
NO2
 molecules
will
collide
to
form
N2O4.


 –  At
the
beginning
of
the
reac-on,
there
is
no
NO2
so
the
reverse
 reac-on
(2NO2(g)
→
N2O4(g))
does
not
occur.
 6 7 Chemical Equilibrium: Example N 2O4 ( g) ⇔ 2 NO2 ( g) N 2O4 → 2 NO2 Rate = k f [ N 2O4 ] 2 NO2 → N 2O4 Rate = k r [ NO2 ]2 [ NO2 ]2 k f ⇒ = = equilibrium cons tan t [ N 2O4 ] kr € (1)
At
long
-mes,
the
macroscopic
concentra-ons
 do
not
change.


 (2)
For
equilibrium
to
occur,
the
system
must
 be
closed.
 (3)
At
equilibrium,
the
ra-o
of
concentra-ons

 equals
a
constant.
 8 constant 9 •  No
maSer
the
star-ng
composi-on
of
reactants
and
 products,
the
same
ra-o
of
concentra-ons
is
achieved
at
 equilibrium.
 •  For
a
general
reac-on
 
the
equilibrium
constant
expression
is
 
where
Kc
is
the
equilibrium
constant.
 10 The following diagrams represent a hypothetical reaction A ↔ B, with A and B represented as red and blue spheres, respectively. The sequence from left to right shows the system as time passes. Do the diagrams indicate that equilibrium has been reached? 11 The following diagrams represent a hypothetical reaction A ↔ B, with A and B represented as red and blue spheres, respectively. The sequence from left to right shows the system as time passes. Do the diagrams indicate that equilibrium has been reached? Yes. The last two panels have the same number of A and B molecules. 12 Example: The Haber Process N2(g) + 3 H2(g) ↔ 2 NH3(g) Nitrogen and hydrogen form ammonia at high pressures and temperatures. But the ammonia also dissociates back into nitrogen and hydrogen. At equilibrium, all three species are present. The equilibrium condition is reached independent of the starting conditions. 13 Fritz Haber (1868-1934) Karl Bosch (1874-1940) The ammonia is used as plant fertilizer. Haber developed the chemistry and Bosch the industrial manufacturing. 14 EXAM ON FRIDAY, 4th MARCH 2011 Understand the basic concepts Read the Question Work on Concepts as fast as you can Work on Problems next DO NOT SPEND MORE THAN 5 Min FOR ANY PROBLEM Make sure to go through the entire exam booklet 15 ...
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