Electrochemistry  G = Electrical work w = n = w max # moles e - F =charge on 1 mol e -  = electrical potential - nF  w max =  H - T  S

Electrochemistry electrons ose lectrons xidation ain lectrons eduction reduction oxidation LEOLEO GERGER Ger

Electrochemistry silver Ag(s) aluminum Al(s) Ag(s)  Al(s)  these are reactions  G =  G o f = a) oxidation b) reduction Ag + (aq) Al 3+ (aq) 77 kJ mol kJ mol -1 Ag + (aq)+ e - ofof Al 3+ (aq) + 3e -

Ag(s)  Ag + (aq) + e - Al(s)  Al 3+ (aq) + 3e -  G o f = 77 kJ mol -1  G o f = -481 kJ mol -1 Al(s)  Al 3+ (aq) + 3e -  G o f = -481 kJ mol -1 Ag + (aq) + e -  Ag(s)  G o = -77 kJ mol -1 3( ) __________________ ________________ 3Ag +  G o = spontaneous + Al  3Ag +Al kJ/mol

1 molecule Al 3+ 3Ag + + Al  Al Ag 1M AgNO 3 1M Al(NO 3 ) 3 Ag Al Ag + + e -  AgAl  Al e - 3e -  a) oxidation b) reduction reduction K+K+ Cl - anodecathode 1 mol Al mol NO 3 -

1 molecule Al 3+ 1M AgNO 3 1M Al(NO 3 ) 3 Ag Al Ag + + e -  AgAl  Al e - 3e -  a) oxidation b) reduction reduction K+K+ Cl - anodecathode 1 mol Al mol NO 3 - Al(s)  Al 3+ (1 M)  Ag + (1 M)  Ag(s)

Reduction Potential Al (s)  Al 3+ (aq) (1M)  Ag + (aq) (1M)  Ag (s) 3Ag + + Al  3Ag + Al 3+  G o =  o =  G o = -712 kJ/mol w max = Al(s)  Al e - Ag + + e -  Ag standard reduction potential standard =1M, 1 atm reduction potential =tendency to gain e - w max -n F  o

half-reaction  o (V) F 2 is spontaneously Li is spontaneously  o = 0 Standard Hydrogen electrode spontaneous reduction spontaneous oxidation (SHE) F 2 + 2e -  2F Ag + + e -  Ag 0.80 Cu e -  Cu H + + 2e -  H Sn e -  Sn Li + + e -  Li Al e -  Al reduced oxidizedLi is a agentreducing a) oxidizing b) reducing F 2 is an agent

half-reaction  o (V) F 2 + 2e -  2F Ag + + e -  Ag0.80 Cu e -  Cu0.34 2H + + 2e -  H Sn e -  Sn Al e -  Al Li + + e -  Li Al half-cell and Ag half-cell reduction reaction: Ag + + e -  Ag oxidation reaction: Al  Al e  o (V) a) b) 3( )  o is intensive _____________ ____ 3Ag +  o cell = +Al  3Ag+Al V

 o cell  o cell =  o red -  o ox Ag + (aq) + e -  Ag(s) Al 3+ (aq) + 3e -  Al(s)  o = 0.80 V  o = V  o cell = (-1.66) = 2.46 V  o cell > 0  o cell < 0 voltaic or galvanic cell spontaneous electrolytic cell non-spontaneous

Electrochemical work 3Ag + + Al  3Ag + Al 3+  o cell = 2.46 V  G o = w max = - n = mol of e -  G o = = CV n F = faraday = 96,500 C / mol e - F  o = standard reduction potential V (J/C) oo -(3 mol e - )(96,500 C/mol e - ) (2.46V) = J= -712 kJ

Balancing redox reactions Cr 2 O 7 2- (aq) balance O balance H balance charge balance Cr Cr 2 O 7 2-  Cr 3+ 2 add H 2 O + H 2 O 7 add H + H add e - e  Cr 3+ (aq)

Cr 2 O H e -  2 Cr H 2 O oxidation or reduction oxidation state of Cr O = 2- Cr 2 O 7 2- Cr 3+ Cr has been Cr is an agent 6+3+ reduced oxidizing

Cr 2 O H e -  2 Cr H 2 O oxidation or reduction GER gain e - reduction need oxidation reaction 2H + (aq)  H 2 (g) balance charge with e - 2H + + 2e -  H 2 (g) another reduction reaction H 2 (g)  2H + (aq) + 2e - () 3