Concerning equilibrium, free energy changes, Le Châtelier's principle

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CONCERNING EQUILIBRIUM, FREE ENERGY CHANGES, LE CHATELIER'S PRINCIPLE

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( AthemEd,

Submitted by: William H. Eberhardt, Georgia Institute of Technology, Atlanta Checked by: David B. Moss, Hiram College, Hiram, Ohio

PREPARATION

REMARKS

Obtain a 2-liter separatory funnel, 0 1 M CuSO., 0.2 M KI, CCL, NH, (cone).

The above observations may now be diacuased in terms of the reaction riff0 = -5.49 kcal (1) '/A C u + + 21- = CuI

DEMONSTRATION Consider the reaction between Cu++ and I-. In the funnel place 100 ml of 0.1 M CuS04 and 800 ml water, containing a drop of acid to prevent hydrolysis. Add freshly prepared 0.2 M KI until the solution turns yellowish green and becomes somewhat dirty. On adding approximately 400 ml of the 0.1 M CuSOi, the solution gets greener and dirtier. The addition of 100 ml of CC14with vigorous shaking causes the iodine to appear in the CCL layer. Further shaking causes the color of iodine to deepen.

+

+

(Note the standard free energies of formation below.) Discuss the shift in equilibrium due to added Cu++; also to the removal of Is by CC14. Now can one shift the equilibriun~back by removing Cu++? Add NHg (cone) to Cu++ in a separate flask. Observe. Finally, add NHa (cone) to the mixture in the funnel and shake. The iodine color leaves the CCL layer and the liquid above becomes clear deep blue in color and the dirt disappears. Cu++

+ 4NHi

= Cu(NHi),++

A G O = -29.9 kcal (2)

Standard free energies of formation:

Journal of Chemical Education June 1964

METALLIC REDUCTION OF AQUEOUS HYDROGEN CHLORIDE Submitted by: Noojin Walker, Jr., Pensacola Junior College, Penaacola, Florida Checked by: David B Moss, Hiram College, Hiram, Ohio

PREPARATION Obtain a medium size test tube (50 mi), 10 ml of 1.0 M HC1 (10 meq), phenolphthalein, a piece of calcium metal weighing about 0 3 g (15 meq)

DEMONSTRATION Pour the acid into the test tube and add two or three drops of indicator. Add the calcium and observe. There is a continual evolution of hydrogen, but midway in the reaction a precipitate begins to form and the solution turns pink.

REMARKS The mit a1 leaction is between the metal and the hydrogen ion, Ca+2H+ = Ca+++H, (Note Ea potentials below )

After d l the H' ion ha8 been reduced. the remainine metal

with other metals such as magnesium, manganese, and zinc

Standard oxidation-reduction potentials (volts) Ca = Ca++ 202 87 0 00 H, = 2H+ 2eHi 2OH- = 2H.O 2e- 0 83 Mg = ME++ 2e2 37 (similar t o Ca, hut requires 10

+

+ + +

+

Mn = Mu++ 2eZn = Zn++ 2e-

+

+

mini

1 18 (forms an insoluble oxide) 0 76 (does not react with water)