Download presentation

Presentation is loading. Please wait.

Published byLandon Applegarth Modified over 2 years ago

1
19.2 Galvanic Cells 19.3 Standard Reduction Potentials 19.4 Spontaneity of Redox Reactions 19.5 The Effect of Concentration on Emf 19.8 Electrolysis Chapter 19 Electrochemistry Semester 2/2013 Ref: http://www.mhhe.com/chemistry/chang

2
19.2 Galvanic Cells Spontaneous(natural) redox reaction anode oxidation cathode reduction

3
Cell = half-cell + half – cell OxidationReduction AnodeCathode In Galvanic cell … Zn (s) + Cu 2+ (aq) Cu (s) + Zn 2+ (aq) Zn is oxidized to Zn 2+ ion Zn electrode is Anode (Reducing Agent) Cu 2+ is reduced to Cu Cu electrode is Cathode (Oxidizing Agent)

4
Galvanic Cells The difference in electrical potential between the anode and cathode is called: cell voltage electromotive force (emf) cell potential Cell Diagram Cell Equation Zn (s) + Cu 2+ (aq) Cu (s) + Zn 2+ (aq) [Cu 2+ ] = 1 M & [Zn 2+ ] = 1 M Cell Notation Zn (s) | Zn 2+ (1 M) || Cu 2+ (1 M) | Cu (s) anodecathode

5
Standard Electrode Potentials Zn (s) | Zn 2+ (1 M) || H + (1 M) | H 2 (1 atm) | Pt (s) 2e - + 2H + (1 M) H 2 (1 atm) Zn (s) Zn 2+ (1 M) + 2e - Anode (oxidation): Cathode (reduction): Zn (s) + 2H + (1 M) Zn 2+ + H 2 (1 atm)

6
19.3 Standard Reduction Potentials Standard reduction potential (E 0 ) is the voltage associated with a reduction reaction at an electrode when all solutes are 1 M and all gases are at 1 atm. E 0 = 0 V Standard hydrogen electrode (SHE) 2e - + 2H + (1 M) H 2 (1 atm) Reduction Reaction

7
E 0 = 0.76 V cell Standard emf (E 0 ) cell 0.76 V = 0 - E Zn /Zn 0 2+ E Zn /Zn = -0.76 V 0 2+ Zn 2+ (1 M) + 2e - Zn E 0 = -0.76 V E 0 = E H /H - E Zn /Zn cell 00 + 2+ 2 Standard Electrode Potentials E 0 = E cathode - E anode cell 00 Zn (s) | Zn 2+ (1 M) || H + (1 M) | H 2 (1 atm) | Pt (s)

8
Standard Electrode Potentials Pt (s) | H 2 (1 atm) | H + (1 M) || Cu 2+ (1 M) | Cu (s) 2e - + Cu 2+ (1 M) Cu (s) H 2 (1 atm) 2H + (1 M) + 2e - Anode (oxidation): Cathode (reduction): H 2 (1 atm) + Cu 2+ (1 M) Cu (s) + 2H + (1 M) E 0 = E cathode - E anode cell 00 E 0 = 0.34 V cell E cell = E Cu /Cu – E H /H 2++ 2 000 0.34 = E Cu /Cu - 0 0 2+ E Cu /Cu = 0.34 V 2+ 0

9
Note: The more positive E 0 the greater the tendency for the substance to be reduced The half-cell reactions are reversible The sign of E 0 changes when the reaction is reversed Changing the stoichiometric coefficients of a half-cell reaction does not change the value of E 0

10
19.4 Spontaneity of Redox Reactions G = -nFE cell G 0 = -nFE cell 0 n = number of moles of electrons in reaction F = 96,500 J V mol = 96,500 C/mol G 0 = -RT ln K = -nFE cell 0 E cell 0 = RT nF ln K (8.314 J/K mol)(298 K) n (96,500 J/V mol) ln K = = 0.0257 V n ln K E cell 0 = 0.0592 V n log K E cell 0 E 0 cell > 0 spontaneous reaction

11
Spontaneity of Redox Reactions

12
19.5 The Effect of Concentration on Cell Emf G = G 0 + RT ln Q G = -nFE G 0 = -nFE 0 -nFE = -nFE 0 + RT ln Q E = E 0 - ln Q RT nF Nernst equation At 298 K ln = 2.303log - 0.0257 V n ln Q E 0 E = - 0.0592 V n log Q E 0 E =

13
19.8 Electrolysis is the process in which electrical energy is used to cause a non spontaneous chemical reaction to occur.

14
Electrolysis of Water 19.8

15
Electrolysis and Mass Changes Quantitative Aspects Case (i) Na + + 1eNa 1 mol. of electron produces 1 mol of Na Atom(22g) 1 F (96500 C) Case (ii) Mg 2+ + 2eMg 2 mol. of electron produces 1 mol of Mg Atom(24g) 2 F (2x 96500C) Case (iii) Al 3 + + 3eAl 3 mol. of electron produces 1 mol of Al Atom(26g) 3 F (3 x 96500 C)

16
charge ( C ) = current (A) x time (s) 1 mole of electron = 96500 coulomb 1 mol. of Na atom = 22 g 1 mol. of Mg atom = 24 g 1 mol. of Al atom = 26 g

Similar presentations

Presentation is loading. Please wait....

OK

Chapter 17 Electrochemistry

Chapter 17 Electrochemistry

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on coordinate geometry for class 9 download Ppt on pi in maths class Download ppt on verb in hindi Ppt on loan against property Ppt on integrated child development scheme Ppt on channels of distribution chart Ppt on project tiger free Ppt on business plan for new business Ppt on adobe photoshop tools Ppt on medieval history of india