Electrochemistry

1
Electrochemistry
2
Definitions

• Oxidation Loss of Electrons
• Reduction Gain of Electrons
• To help LEO (Loss of electrons Oxidation) the
  Lion says GER (Gain of electrons Reduction)
• Oxidation Numbers are numbers assigned to atoms
  that keep track of the charge. Can be negative,
  neutral, or positive.

3
Definitions

• Oxidizing Agent causes another atom to become
  oxidized.
• Reducing Agent causes another atom to become
  reduced.
• Redox reaction is a reaction where electron
  transfer are done.
• Half reaction method assist in balancing the
  redox reactions.

4
Definitions

• Anode the electrode at which oxidation occurs.
• Cathode the electrode at which reduction
  occurs.
• Voltaic Cells have a DG and are spontaneous
  favorable
• Electrolytic Cells have a DG and are not
  spontaneous unfavorable.

5
The Charge of Elements

• The charge of free elements are zero. Example
  N2, P4, S8
• The oxidation number of ions is equal to the
  charge of the ion.
• Charges of atoms can change thought a reaction.

6
Charges
1
0
                                 
                     
                     
 
 
 
                 
1 H
2 He
3
4
-3
-2
-1
2
5 B
6 C
7 N
8 O
9 F
10 Ne
3 Li
4 Be
15 P
16 S
17 Cl
18 Ar
14 Si
11 Na
12 Mg
13 Al
30 Zn
31 Ga
32 Ge
33 As
34 Se
29 Cu
35 Br
19 K
20 Ca
22 Ti
23 V
24 Cr
25 Mn
27 Co
36 Kr
28 Ni
21 Sc
26 Fe
46 Pd
51 Sb
37 Rb
38 Sr
39 Y
40 Zr
41 Nb
43 Tc
44 Ru
45 Rh
47 Ag
48 Cd
49 In
50 Sn
52 Te
53 I
54 Xe
42 Mo
55 Cs
56 Ba
57 La
72 Hf
73 Ta
74 W
75 Re
76 Os
77 Ir
78 Pt
79 Au
80 Hg
81 Tl
82 Pb
83 Bi
84 Po
85 At
86 Rn
87 Fr
88 Ra
89 Ac
104 Rf
105 Db
106 Sg
107 Bh
109 Mt
110 Ds
108 Hs
Shells (1, 2, 3, 4, 5, 6)
Orbital (2p)
7
Half-Reaction Method

• Redox Reaction
• 2I- ? I2 2(e) electrons
• The charge of 2I- -2. If you oxidize 2I- by 2
  electrons then you receive I2.

8
Redox Reaction

• MnO4- 8H ? Mn2 4H2O
• MnO4- - oxidation state for Mn 7
• Mn2 - oxidation state for Mn 2
• Difference between reactant and product is 5
  electron reduction (GER).

9
Voltaic Cells

• Think of voltaic cell as kids playing hot potato.
  The Zn metal wants to give up its electrons.
  Those two electrons travel through the wire to
  the Cu metal which converts the Cu2 into Cu
  metal and adds it to the Cu metal.

10
Voltaic Cells

• These reactions are favorable with a negative DG.
  When DG is negative then the reaction is
  favorable. When DG is positive then the reaction
  is unfavorable.

11
Voltaic Cells
Salt Bridge
The Salt bridge helps to balance the counter ions
of the solution.
12
Electrolytic Cells

• In Electrolytic cell which are similar to voltaic
  cells the DG is positive and the reactions are
  unfavorable so an energy source (battery) is
  added to start the process.

13
General Understanding

• G is the Gibbs free energy which during a
  reaction changes. This change is defined as DG.
  D means change. If the overall change is
  negative from product to reactants then the
  reactions wants to go. If the change is positive
  then the reaction is unfavorable. If you see an E
  in the equation this is related to DG by this
  equation.

DG -nFE