Experiment 3Abis, Ralph John Baylon, Basil

When a stress is brought to bear on a system at equilibrium, the system tends to change so as to relieve the stress.

The stress being described in the principle refers to a change in the following that REMOVES the system from EQUILIBRIUM:CONCENTRATION PRESSURE and VOLUME TEMPERATURE

The DIRECTIONAL SHIFT of EQUILIBRIUM depends on the ASSOCIATION OF THE STRESS between Products or Reactants.

Shift to the LEFT/REACTANTS? If change in concentration favors the reactants. Shift to the RIGHT/PRODUCTS? If change in concentration favors the products.

DOES NOT AFFECT SOLUTIONS IN CONDENSED PHASES (like aqueous solutions) since LIQUIDS and SOLIDS are virtually INCOMPRESSIBLE.

For GASES,Concentrations are greatly affected by changes in pressure. Increased pressure (decreased volume) = REVERSE reaction Decreased pressure (increased volume) = FORWARD reaction Gas concentration may be altered without changing the volume by adding an INERT GAS to the equilibrium system.

Equilibrium constant K Changes in concentration, pressure, or volume does not affect the value of K. ENDOTHERMIC = INCREASE IN TEMP EXOTHERMIC = DECREASE IN TEMP

No effect at all Manifestation in the LOWERING of Ea of the reaction, permitting the reaction to REACH EQUILIBRIUM IN THE SHORTEST TIME POSSIBLE.

Combine the following in a small test tube: 1.0 mL 2.0M Cu(NO3)2 1.0 mL 2.0M NH4OH 5 mL H20 Chemical Reaction? Cu2+(aq) + 4 NH3(aq) Cu(NH3)42+(aq)

SKY BLUE!

SYSTEM S A B C D E F G H I

Reagent Light blue 0.1 M Cu(NO3)2 0,1 M NH4OH 0.1 M K4Fe(CN)6 0.1 M HCl 0.1 M NaOH 0.1 M NaNO3 Cold temperature 6.0 M HCl, 3.0 M NaOH 0.1 M Pb(NO3)2 and 6.0 M HCl

SYSTEM S A B C D E F G H I

OBSERVATIONS Light blue Darker than S Darker than S Brown precipitate Lighter than S Lighter than S Light blue Darker than S Yellow to orange to yellow Yellow to precipitate , back to yellow solution

CONTENT: H2O SHIFT: n/a OBSERVATION: Light Blue Standard for comparison Cu(NH3)42+

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.

CONTENT: 0.1 M NH4OH SHIFT: Forward OBSERVATION: Darker than S DISCUSSION: Common ion: NH3 Increased moles of reactants, higher concentration of products.

CONTENT: 0.1 M K4Fe(CN)6 SHIFT: BACKWARD OBSERVATION: Formation of Brown precipitate DISCUSSION: Cu2+ reacted with Fe(CN6)4-, consuming Cu2+ Counteraction to reaction resulted to backward shift Cu2Fe(CN6) is responsible for color

CONTENT: 0.1 M HCl SHIFT: Backward OBSERVATION: Lightest blue of all solutions DISCUSSION: HCl dissociated into H+ and ClH+ reacted with NH3 and consuming NH3

CONTENT: 0.1 M NaOH SHIFT: Backward OBSERVATION: Lighter than S DISCUSSION: Consumption of Cu2+ Dissociation of NaOH to Na+ and OHCu2+ + OH- Cu(OH)2

CONTENT: 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.

CONTENT: 0.1 M Cu(NO3)2 SHIFT: Forward OBSERVATION: Darker than S DISCUSSION: Reaction is exothermic Decreasing temperature will cause FORWARD SHIFT, hence the darker color.

Cu2+ + 4NH3 [Cu(NH3)4]2+ + heat

CHANGE IN COLOR? Yellow to Orange INDICATE CHANGE IN COLOR. Orange to Yellow EQUATION FOR EQUILIBRIUM? 2 CrO42- + 2 H+ Cr2O72- + H2O

SPECIES PREDOMINATING IN ACID SOLUTION? Cr2O72SPECIES PREDOMINATING IN BASIC SOLUTION? CrO42-

EQUATION? CrO42- + Pb2+ PRECIPITATE? PbCrO4

PbCrO4

COLOR OF PRECIPITATE? Yellow

The position of an equilibrium shifts in the direction where the stress applied to the system will be relieved. The change in enthalpy determines how temperature change affects the equilibrium.

Use of an indicator which shows a change in color, not just in intensity to demonstrate Le Chateliers principle. For effect of change in temperature, use CO(H2O)62+ and CoCl42-.pink when cooled -> more CO(H2O)62+ blue when heated-> more CoCl42-