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Lecture 18.2b- Le Chatelier's Principle
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Lecture 18.2b- Le Chatelier's Principle

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Section 18.2 Lecture (part B) for Honors & Prep Chemistry

Section 18.2 Lecture (part B) for Honors & Prep Chemistry

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Transcript

  • 1. Bellwork‐
Equilibrium The
system
described
by
the
equa8on H2O(l)

H2O(g)






ΔH=
40.7
kJ is
at
equilibrium. a)How
does
the
concentra8on
of
H2O
gas change? b)Does
condensa8on
occur? c)
Does
vaporiza8on
occur? d)What
condi8ons
must
be
met
for
equilibrium to
occur?
  • 2. Bellwork The
system
described
by
the
equa8on H2O(l)

H2O(g)






ΔH=
40.7
kJ is
at
equilibrium. a)How
does
the
concentra8on
of
H2O
gas
change? it
doesn’t,
at
equilibrium
concentra8ons
are
constant b)Does
condensa8on
occur? YES c)
Does
vaporiza8on
occur? 




YES,
at
the
same
rate
that
condensa8on
occurs d)What
condi8ons
must
be
met
for
equilibrium
to occur?Closed
container,
stable
temperature,
low
Ea
  • 3. A
system
is
at
equilibrium
due
to
a balancing
of
many
factors. Changing
the
condi8ons
of
a
system
at equilibrium
will
“shiT”
the
equilibrium. A
“shiT”
is
when
EITHER more
products
are
formed
 (forward
reac8on
speeds
up) OR more
reactants
are
formed
 (reverse
reac8on
speeds
up)
  • 4. Le
Chatelier’s
Principle When
an
equilibrium
system
is disturbed
the
equilibrium
will
shiT
to undo
the
disturbance.
  • 5. Changing
concentra8ons 


H2(g)
+
Cl2(g)
↔
2HCl(g) Increasing
H2
or
Cl2
concentra8on
will
shiT the
equilibrium
to
the
right
(more products)
because
this
counteracts
the addi8on
of
reactant. EXAMPLE‐
Increasing
[HCl]
will
shiT
the equilibrium
to
the
leT
(towards
reactants). GETS
RID
OF
extra
HCl! What
about
decreasing
concentra8ons?
  • 6. Le
Chatelier’s
Principle Whatever
is
done
to
an
equilibrium system
will
be
partly
undone.
  • 7. Changing
pressure 



N2O4(g)
↔
2NO2
(g) 1
mole
of
gas
↔
2
moles
of
gas Increase
pressure
–
shiTs
leT (less
moles
of
gas
will
decrease
pressure) Decrease
pressure
–
shiTs
right (more
moles
of
gas
will
increase
pressure) UNDER
PRESSURE‐
SHIFT
TO
LESS
MOLES Of
gas!
  • 8. Changing
pressure
only
affects equilibrium
if
products
have
a different
number
of
gas
moles
than reactants. H2O(l)  H2O(g) 0 gas moles 1 gas mole
  • 9. Changing
temperature Write
equa8on
with
energy
as
a
product
or reactant. Endothermic Energy
+
A
+
B
↔
C
+
D Increase
temp
–
favors
forward
(shiT
to
the right)
because
that
uses
up
the
added energy Decrease
Temp?
  • 10. Changing
temperature Exothermic A
+
B
↔
C
+
D
+
Energy Increase
temp
–
favors
reverse
reac8on and
a
shiT
to
the
leT
because
that
uses up
the
added
energy Decrease
temp?
The
system
will
do
what it
can
to
get
more
energy.
  • 11. A catalyst will not affect the equilibrium position (a.k.a. shift the equilibrium). A catalyst will increase the reverse reaction rate as much as it increases the forward reaction rate. The system will reach equilibrium faster, but the final concentrations of reactants and products are not changed by the addition of a catalyst.
  • 12. Changing
concentra8on
does
not affect
pure
liquids
or
solids. Changing
pressure
only
affects gases.
  • 13. 18. 2The
equilibrium
constant
(Keq)
is
a
ra8o of
product
concentra8ons
to
reactant concentra8ons
at
equilibrium. For aA + bB  cC + dD Keq = [C]c[D]d [A]a [B]b

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