CHEMICAL EQUILIBRIUM: occurs in a reversible reaction, when the FORWARD reaction rate equals the REVERSE reaction rate.

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CHEMICAL EQUILIBRIUM 3/12/07

• CHEMICAL EQUILIBRIUM occurs in a reversible
  reaction, when the FORWARD reaction rate equals
  the REVERSE reaction rate.
• When equilibrium is established, the amounts of
  reactants and products present are termed the
  equilibrium concentrations.
• There will be un-reacted reactants at
  equilibrium.
• Many reactions produce little product before
  equilibrium is reached.
• The equilibrium constant ( K ) indicates the
  extent to which the reaction produces product. K
  values greater than 1 favor high product
  equilibrium concentrations. K values less than
  one indicate the reactants are favors to be the
  predominant species at equilibrium.
• Equilibrium reactions will have a double arrow ?
  ?. NOTE equilibrium is a reversible chemical
  change in a chemical reaction.

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• Equilibrium also occurs in physical changes such
  as phase changes. This is called phase
  equilibrium, the equilibrium of twp phases at the
  same time at the same temperature.
• Le Chateliers Principle
• States that a system (reaction) at equilibrium
  will resist any external change (stress) that is
  applied. Stresses include any change in
  Temperature, Pressure or changing the
  concentrations of any species in the reaction.
• Le Chateliers Algorithms
• If you add to one side of the arrow, the
  equilibrium shifts (runs) to the opposite side of
  the arrow.
• If you remove something on one side of the arrow,
  the equilibrium will run to the same side.

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• EXAMPLES THE EFFECT OF TEMPERATURE ON
  EQUILIBRIUM REACTIONS.
• What happens if you increase the temperature
  of the following EXOTHERMIC (Q- ) reaction?
• A 2B ? ? C D

RULE Heating an exothermic reaction drives it in
reverse, cooling it drives it in forward.
Write heat on the PRODUCT side of an exothermic
reaction, apply the algorithm as if heat were a
chemical species.
Heat is on the RIGHT of the reaction, you added
to the RIGHT, therefore the reaction shifts LEFT,
runs in reverse. The heat is consumed. What you
add, the reaction tries to get rid of .
HEAT
X 2X -X -X
REACTION RUNS IN REVERSE, CONSUMES ADDED HEAT,
shift away form an addition
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RULE cooling an endothermic reaction drives it
in reverse, warming it drives it forward.
What happens if you increase the temperature of
the following ENDOTHERMIC (Q ) reaction?
A 2B ? ? C D
Heat is on the LEFT of the reaction, you added to
the LEFT, therefore the reaction shifts RIGHT,
runs in forward direction. The heat is consumed.
What you add, the reaction tries to get rid of .
For endothermic reactions write heat on the
REACTANT side of the reaction, apply the
algorithm as if it were a chemical species.
HEAT
-X -2X X X
THIS REACTION RUNS FORWARD. Shift away from an
addition.
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RULE cooling an endothermic reaction drives it
in reverse, warming it drives it forward.
What happens if you DECREASE the temperature of
the following ENDOTHERMIC (Q ) reaction?
A 2B ? ? C D
Heat is on the LEFT of the reaction, you REMOVED
from the LEFT, therefore the reaction shifts
LEFT, runs in reverse direction. The heat is
consumed. What you remove, the reaction tries to
replace.
For endothermic reactions write heat on the
REACTANT side of the reaction, apply the
algorithm as if it were a chemical species.
HEAT
X 2X -X -X
REACTION SHIFS LEFT, TO A REMOVAL (SUBTRACTION).
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RULE cooling an Exothermic reaction drives it in
FORWARD, warming it drives it in REVERSE.
What happens if you DECREASE the temperature of
the following EXOTHERMIC (Q - )
reaction? H2O(l) ? ? H2O(s)
Heat is on the right of the reaction, you REMOVED
from the RIGHT, therefore the reaction shifts
LEFT, runs in forward direction. The heat is
consumed. What you remove, the reaction tries to
replace.
For Exothermic reactions write heat on the
PRODUCT side of the reaction, apply the algorithm
as if it were a chemical species.
HEAT
-X X
THIS REACTION RUNS IN FORWARD. SHIFT TO A REMOVAL
(COOLING REMOVES HEAT).
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RULE IF A SPECIES IS REMOVED ONE SIDE OF THE
REACTION, THE EQUILIBRIUM, WILL RUN TO THE SAME
SIDE OF THE ARROW, THE SYSTEM WILL REPLACE WHAT
WAS REMOVED.
Example, for the reaction below, what will happen
if the molarity of A is REDUCED? A 3B ? ? 2C
D -X
3X -2X -X
A IS REMOVED FROM THE LEFT, THERFORE THE REACTION
SHIFTS TO THE LEFT
THE CHANGES THAT OCCUR AFTER THE A IS DECREASED
THE EQUILIBRIUM CONCENTRATION AFTER A NEW
EQUILIBRIUM IS ESTABLISHED
X 3X -2X -X
REACTION RUNS IN REVERSE, REPLACES SOME OF
REMOVED A. SHIFTS TO A REMOVAL (DECREASED
CONCENTRATION)
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RULE IF A SPECIES IS ADDED TO ONE SIDE OF THE
REACTION, THE EQUILIBRIUM, WILL RUN TO THE
OPPOSITE SIDE OF THE ARROW, THE SYSTEM WILL
CONSUME WHAT WAS ADDED.
Example, for the reaction below, what will happen
if the molarity of A is increased? A 3B ? ?
2C D X
-3X 2X X
A IS ADDED TO THE LEFT, THERFORE THE REACTION
SHIFTS TO THE RIGHT
THE CHANGES THAT OCCUR AFTER THE A IS INCREASED
THE EQUILIBRIUM CONCENTRATION AFTER A NEW
EQUILIBRIUM IS ESTABLISHED
-X -3X 2X X
THIS REACTION RUNS IN FORWARD. SHIF AWAY FROM AN
ADDITION (INCREASED CONCENTRATION