Lecture 33

Lecture 33 - 4/8/10 e.g. Find !Gf for I-(aq) given the...

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4/8/10 1 25 e.g. Find ! G f ° for I - (aq) given the following standard cell at 298 K: I 2 (s) + 2OH - (aq) + H 2 (g) ! 2 I - (aq) + 2 H 2 O (l) Anode : 2 H 2 O (l) + 2e - ! 2OH - (aq) + H 2 (g) cell = 0.535 V – (-0.828) V = +1.363 J/C ! G ° = -nFE ° = -(2 mol e-)(96485 C/mol e-)(1.363 J/C) ! G ° = - 263.0 kJ Cathode: I 2 (s) + 2e - (aq) ! 2 I - (aq) E° = 0.535 V E° = -0.828V 26 ! G o = n p ! G f o ( p ) " # n r ! G f o ( r ) " ! G o = 2mol "! G f °(I - )+2mol "! G f °(H 2 O(l)) # [2mol "! G f °(OH - ) + 1mol "! G f °(I 2 (s)) + 1mol "! G f °(H 2 )] ! G f °(I - ) = -51.6 kJ ! G f °(I - ) = {-263.0 # 2mol " (-237.1 kJ/mol) + [2mol " (-157.2 kJ/mol)+ 1mol " (0) + 1mol " (0)]}/2 5.5. Nernst Equation : Non-standard conditions Need to vary concentrations of species in the cell When conc. is not 1 M, change in reactant/product concentrations can change cell voltage from standard value. Recall:
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Lecture 33 - 4/8/10 e.g. Find !Gf for I-(aq) given the...

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