Chap15-Part2

Chap15-Part2 -...

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Unformatted text preview: EXAM‐3:
April
15th
Friday
2011
(not
April
11th)
 Syllabus:
Chapters
15,
16
and
17
  
Exam
‐2
Grades
Online
  
KEY
will
be
posted
by
tonight
  
Exam‐1
Grades
curved

 1
 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 € 2
 •  No
maAer
the
starBng
composiBon
of
reactants
and
 products,
the
same
raBo
of
concentraBons
is
achieved
at
 equilibrium.
 •  For
a
general
reacBon
 
the
equilibrium
constant
expression
is
 
where
Kc
is
the
equilibrium
constant.
 3 Law
of
Mass
AcHon
 The
law
of
mass
acBon
is
universal,
applicable
under
any
circumstance.
However,
for
 reacBons
that
are
complete,
the
result
may
not
be
very
useful.
Here
is
the
mass
acBon
 law
by
using
a
general
chemical
reacBon
equaBon
in
which
reactants
A
and
B
react
to
 give
product
D
and
E.
 where 
 
a,
b,
d,
e
=
small
integers
 
 
 
[A],
[B],
[D],
[E]
=
equilibrium
concentraBons
 
 
 
 
in
units
of
M
 
 
Kc
=
“the
equilibrium
constant”
 (a)  The
relaBonship
between
the
equilibrium
concentraBons
and
the
equilibrium

 constant
depends
only
on
the
stoichiometry
of
the
reacBon
and
not
the
mechanism.
 (b)
The
equilibrium
constant
does
depend
on
the
temperature.
 4
 Law
of
Mass
AcHon
 Cato
Maximilian
Guldberg
(1836‐1902)
&
Peter
Waage
(1833‐1900)
 5
 N2O4(g)

↔
2
NO2(g)
 6
 Consider
the
reacBon
A
+
B
↔
C
+
D.

Assume
that
both
the

 forward
and
reverse
reacBons
are
elementary
steps
and
that
the

 value
of
the
equilibrium
constant,
Kc,

is
very
large.
 (a)
Which
species
predominate
at
equilibrium,
reactants
or
products?
 (b)
Which
reacBon
has
the
larger
rate
constant,
the
forward
 or
the
reverse?
 7
 Consider
the
reacBon
A
+
B
↔
C
+
D.

Assume
that
both
the

 forward
and
reverse
reacBons
are
elementary
steps
and
that
the

 value
of
the
equilibrium
constant,
Kc,

is
very
large.
 (a)
Which
species
predominate
at
equilibrium,
reactants
or
products?
 products:
 (b)
Which
reacBon
has
the
larger
rate
constant,
the
forward
 or
the
reverse?
 8
 Consider
the
reacBon
A
+
B
↔
C
+
D.

Assume
that
both
the

 forward
and
reverse
reacBons
are
elementary
steps
and
that
the

 value
of
the
equilibrium
constant,
Kc,

is
very
large.
 (a)
Which
species
predominate
at
equilibrium,
reactants
or
products?
 products:
 (b)
Which
reacBon
has
the
larger
rate
constant,
the
forward
 or
the
reverse?
 forward:
 9
 10
 Law
of
Mass
AcHon:

Gas
Phase
 where 
 
a,
b,
d,
e
=
small
integers
 
 
PA,
PB,
PC,
PE
=
equilibrium
parBal
pressures
in
units
of
atm
 
 
Kp
=
“the
equilibrium
constant”
 11
 RelaHonship
Between
Kp
and
Kc
 aA + bB ⇔ dD + eE d e PP K p = D a Eb PA PB PA = [ D]d [ E ]e & Kc = [ A]a [ B]b n A RT n = ( A ) RT = [ A]RT etc . V V ([ D]RT ) d ([ E ]RT ) e [ D]d [ E ]e ( RT ) d ( RT ) e ⇒ Kp = = a b ([ A]RT ) ([ B]RT ) [ A]a [ B]b ( RT ) a ( RT ) b ⇒ K p = K c ( RT ) d + e− a− b L − atm ( R = 0.08206 ) mol − K K p = K c ( RT ) Δn 12
 assume
T
=
500
K
 




**units**
 13
 The
diagram
shows
an
equilibrium

 mixture
in
soluBon
for
the
reacBon

 A
+
X
↔
AX.


 Is
Kc
greater
than
or
less
than
1?
 14
 The
diagram
shows
an
equilibrium

 mixture
in
soluBon
for
the
reacBon

 A
+
X
↔
AX.


 Is
Kc
greater
than
or
less
than
1?
 15
 Consider
the
reacBon
of
carbon
monoxide
 gas
with
chlorine
gas
at
100oC
to
form
 phosgene
gas:
 CO(g)
+
Cl2(g)
↔
COCl2(g)
 Because
the
numerator
is
much
larger
than
 the
denominator,
[COCl2]
>>
[CO][Cl2].
 If
K
>>
1 
“the
equilibrium
lies
to
the
right” 
products
predominate
 If
K
<<
1 
“the
equilibrium
lies
to
the
lej” 
reactants
predominate
 16
 (a)
Write
an
expression
for
Kc
for
the
following
reacBon:
 (b)
Does
the
following
reacBon
lie
to
the
right,
favoring
product
 formaBon,
or
to
the
lej,
favoring
reactant
formaBon?
 17
 (a)
Write
an
expression
for
Kc
for
the
following
reacBon:
 (b)
Does
the
following
reacBon
lie
to
the
right,
favoring
product
 formaBon,
or
to
the
lej,
favoring
reactant
formaBon?
 18
 (a)
Write
an
expression
for
Kc
for
the
following
reacBon:
 (b)
Does
the
following
reacBon
lie
to
the
right,
favoring
product
 formaBon,
or
to
the
lej,
favoring
reactant
formaBon?
 to
the
lej,
favoring
reactant
formaBon
 19
 (1)  The
equilibrium
constant
of
a
reacBon
in
the
reverse
direcBon

 is
the
inverse
of
the
equilibrium
constant
in
the
forward
direcBon.
 20
 (2)
The
equilibrium
constant
of
a
reacBon
that
has
been
mulBplied
 by
a
number
is
the
equilibrium
constant
raised
to
a
power
equal
 to
that
number.
 21
 (3)
The
equilibrium
constant
for
a
net
reacBon
made
up
of
two
or
 more
steps
is
the
product
of
the
equilibrium
constants
for
the
single
 steps.
 22
 Consider
the
equilibrium

 Calculate
the
equilibrium
constant
Kc
for
this
reacBon,
given
that
 23
 Consider
the
equilibrium

 Calculate
the
equilibrium
constant
Kc
for
this
reacBon,
given
that
 24
 Methanol
can
be
produced
by
the
following
reacBon:
 
CO(g)

+
2
H2(g)

↔

CH3OH(g)
 An
equilibrium
mixture
in
a
2.00‐L
container
is
found
to
contain
0.0406
mol
 CH3OH,
0.170
mol
CO,
and
0.302
mol
H2.
Calculate
Kc.
 25
 Methanol
can
be
produced
by
the
following
reacBon:
 
CO(g)

+
2
H2(g)

↔

CH3OH(g)
 An
equilibrium
mixture
in
a
2.00‐L
container
is
found
to
contain
0.0406
mol
 CH3OH,
0.170
mol
CO,
and
0.302
mol
H2.
Calculate
Kc.
 26
 Homogeneous
equilibria
involve
reactants
and
products
in
the
same
phase.
 Examples: 
N2O4(g)

↔
2
NO2(g)

 
 
CO(g)
+
Cl2(g)
↔
COCl2(g)

 
 
CO(g)

+
2
H2(g)

↔

CH3OH(g)
 Heterogeneous
equilibria
involve
at
least
one
reactant
or
product
in
a
different
phase.
 Examples: 
PbCl2(s)

↔

Pb2+(aq)

+

2
Cl‐(aq)
 
 
H2O(l)

+

CO32‐
(aq)

↔

OH‐(aq)

+

HCO3‐(aq)
 
 
CO2(g)

+

H2(g)

↔

CO(g)

+

H2O(l)
 
 
SnO2(s)

+

2
CO(g)

↔

Sn(s)

+
2
CO2(g)
 27
 ...
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This note was uploaded on 09/13/2011 for the course CHEM 102 taught by Professor Todd during the Spring '08 term at UNC.

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