1. Electrochemistry
Chapter 17

2. Electrochemistry and Redox
Oxidation-reduction: “Redox”
Electrochemistry:
study of the interchange between chemical change and electrical work
Electrochemical cells:
systems utilizing a redox reaction to produce or use electrical energy

3. Redox Review Redox reactions: electron transfer processes
Oxidation: loss of 1 or more e-
Reduction: gain of 1 or more e-
Oxidation numbers: imaginary charges
(Balancing redox reactions)

4. Oxidation Numbers (O.N.)
1. Pure element O.N. is zero
2. Monatomic ion O.N. is charge
3. Neutral compound: sum of O.N. is zero
Polyatomic ion: sum of O.N. is ion’s charge
*Negative O.N. generally assigned to more electronegative element

5. Oxidation Numbers (O.N.)
4. Hydrogen
assigned +1
(metal hydrides, -1)
5. Oxygen
assigned -2
(peroxides, -1; OF2, +2)
6. Fluorine
always -1

6. Oxidation-reduction Oxidation is loss of e-
O.N. increases (more positive)
Reduction is gain of e-
O.N. decreases (more negative)
Oxidation involves loss OIL
Reduction involves gain RIG

7. Redox Oxidation is loss of e- causes reduction “reducing agent”
Reduction is gain of e-
causes oxidation
“oxidizing agent”

9. Examples
Acidic conditions:
Basic conditions:

10. Types of cells Voltaic (galvanic) cells:
a spontaneous reaction generates electrical energy
Electrolytic cells:
absorb free energy from an electrical source to drive a nonspontaneous reaction

11. Common Components Electrodes:
conduct electricity between cell and surroundings
Electrolyte:
mixture of ions involved in reaction or carrying charge

12. Electrodes
Anode:
Oxidation occurs at the anode
Cathode:
Reduction occurs at the cathode
Active electrodes: participate in redox
Inactive: sites of ox. and red.

13. Voltaic (Galvanic) Cells
A device in which chemical energy is changed to electrical energy.
Uses a spontaneous reaction.

14. Oxidation
Reduction

17. Zn2+(aq) + Cu(s)  Cu2+(aq) + Zn(s)
Zn gives up electrons to Cu
“pushes harder” on e-
greater potential energy
greater “electrical potential”
Spontaneous reaction due to
relative difference in metals’ abilities to give e-
ability of e- to flow

18. Ecell = V

20. Batteries
A battery is a galvanic cell or, more commonly, a group of galvanic cells connected in series.