Exp 3: Le Châtelier's Principle

8/7/2019 Exp 3: Le Chtelier'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...

Exp 3: Le Châtelier's Principle

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