exp 3: le châtelier's principle
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Le Chatelier's PrincipleExperiment 3
Dacalanio, Teresa
Sison, Angel Abraham
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When a stress isbrought to bear on
a system at
equilibrium, the
system tends to
change so as torelieve the stress.
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The stress being described in the principle
refers to a change in the following thatREMOVES the system from EQUILIBRIUM:
CONCENTRATION
PRESSURE and VOLUME
TEMPERATURE
The DIRECTIONAL SHIFT of EQUILIBRIUMdepends on the ASSOCIATION OF THE
STRESS between Products or Reactants.
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Change in Concentration
Shift to the LEFT/REACTANTS?
If change in concentration favorsthe reactants.
Shift to the RIGHT/PRODUCTS?
If change in concentration favors
the products.
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Change in Pressure or Volume
DOES NOT AFFECT
SOLUTIONS IN CONDENSEDPHASES (like aqueous solutions)
since LIQUIDS and SOLIDS are
virtually INCOMPRESSIBLE.
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For GASES,
Concentrations are greatly affected by changes in
pressure.
Increased pressure (decreased volume) = REVERSE
rxn
Decreased pressure (increased volume) =
FORWARD rxn
Gas concentration may be altered without changing
the volume by adding an INERT GAS to the
equilibrium system.
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Change in Temperature
uili rium n tant K
Change in n entrati n, pre ure, r
lume e n t affe t the alue f K.
eat treate a CT T !
T IC T . I C
X T IC T . C
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Addition of Catalyst
No effect at all
Manifestation in the LOWERING ofEa of the reaction, permitting the
reaction to REACH EQUILIBRIUM
IN THE SOONEST TIME.
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Solution?
Combine the following in a small test tube:
1.0 mL 2.0M Cu(NO3)2
1.0 mL 2.0M NH4
OH5 mL H20
Chemical Reaction?
Cu2+(aq) + 4 NH3(aq) Cu(NH3)42+(aq)
DAR BLUE!
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Position S
CONTENT: H2O
SHIFT: n/a
OBSERVATION: Light Blue
Standard for comparison
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Position A
CONTENT: 0.1 M Cu(NO3)2
SHIFT: Forward
OBSERVATION: Darker than S
DISCUSSION:
Common ion: Cu2+
Increased moles of reactants, higher
concentration of products.
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Position B
CONTENT: 0.1 M NH4OH
SHIFT: Forward
OBSERVATION: Darker than S
DISCUSSION:
Common ion: NH3
Increased moles of reactants, higher
concentration of products.
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Position C
CONTENT: 0.1 M 4Fe(CN)6
SHIFT: BAC WARD
OBSERVATION: Formation of Brown precipitate
DISCUSSION:
Cu2+ reacted with Fe(CN6)4-, consuming Cu2+
Counteraction to reaction resulted to backwardshift
Cu2Fe(CN6) is responsible for color
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Position D
CONTENT: 0.1 M HCl
SHIFT: Backward
OBSERVATION: Lightest blue of all solutions
DISCUSSION:
HCl dissociated into H+ and Cl-
H+ reacted with NH3 and consuming NH3
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Position E
CONTENT: 0.1 M NaOH
SHIFT: Backward
OBSERVATION: Lighter than S
DISCUSSION:
Consumption of Cu2+
Dissociation of NaOH to Na+ and OH-
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Position FCONTENT: 0.1 M NaNO3
SHIFT: No shift
OBSERVATION: No shift
DISCUSSION:
Theoretically, the reagent added should not
react with the reactant. The reagent
dissociated into Na+ and NO3-, which do not
disturb the equilibrium of the system.
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Position G
CONTENT: 0.1 M Cu(NO3)2
SHIFT: Forward
OBSERVATION: Darker that S
DISCUSSION:
Reaction is exothermic
Decreasing temperature will cause
FORWARD SHIFT, hence the darker color.
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Part B, 2
Equation?
CrO42- + Pb2+ PbCrO4
Precipitate?
PbCrO4
Color of precipitate?
Yellow
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Conclusions andRecommendations
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Chem 18.1 is...
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