Electrochemistry

TERMINOLOGY 
Electrode is an electrical conductor that uses to contact with nonmetal part in the circuit 
Electrolyte is a compound that conducts electricity in solution 
Salt Bridge is a tube that contains salt solution (Any kind of salt, KNO3 is common). It connects the Anode and Cathode 
Reduction is the process of GAINING electron(s). Reduced agent is the atom or ion that LOSE electron(s)
Oxidation is the process of LOSING electron(s). Oxidized agent is the ion that GAIN electron(s)

Cathode is an electrode, has a positive charge where Reduction occurs
Anode is an electrode, has a negative charge where Oxidation occurs

MNEMONIC DEVICE: 

 LEO: GER 

(Lion growls)

 (Losing Electron- Oxidation) : (Gaining Electron- Reduction)

CPR : ANO

(Cathode, Positive, Reduction) : (Anode, Negative, Oxidation)

STANDARD CELL NOTATION 

            

              Anode Electrode I Anode Electrolyte II Cathode Electrolyte I Cathode Electrode 

Example: 

Cu-Zn Galvanic Cell
Source: http://en.wikipedia.org/wiki/Galvanic_cell

The Redox Reaction for this Cell:

Zn_(s) + Cu²⁺ _(aq)à Zn²⁺ _(aq) +Cu _(s)

Half Life Reaction

                       Zn_(s)   à Zn²⁺ _(aq) + 2e        Oxidation (Anode)

            Cu²⁺ _(aq) + 2e à Cu _(s)                 Reduction (Cathode)

Standard Cell Notation

Zn_(s) I Zn²⁺ _(aq) II Cu²⁺ _(aq) I Cu _(s) 

REDUCTION POTENTIAL

E^o_CELL = E^o _REDUCTION – E^o _OXIDATION

To Calculate the E^o_CELL, we need to look up the Reduction Potential energy from the table 

Standard Reduction Potentials Table
Source: http://www.jesuitnola.org/upload/clark/refs/red_pot.htm

IMPORTANT: DO NOT flip the sign of E^o when calculating. Keep the same sign as given in the table. 
TRICK: The LARGER the E^o, the easier to become REDUCTION

ΔG^o AND  E^o_CELL 

To determine the reaction is spontaneous or not, we can use the following equation:

Equation  (1)

NOTE: the equation is using a new constant  F = 9.65x10⁴ (J/Vmol) or (Coulomb/mol)  and n IS NOT the mole of solutions but the NUMBER OF MOLES OF ELECTRONS TRANSFERRED in the reaction

From the formula we can conclude that:

 IF E^o_CELL is NEGATIVE, the reaction is NONSPONTANEOUS

 IF E^o_CELL is POSITVE, the reaction is SPONTANEOUS

CELL POTENTIAL AND CONCENTRATION 

When the concentration change, the cell will also be affected because of the K or Q constant of the reactions. 

The following equation will help us to calculate the new potential when the concentrations of solution are changed or find concentrations with given Cell potential

Use only when the reaction is at standard condition 

Use only when the reaction is not at standard condition 

Nernst Equation

Since R,T, and  F are constant, we can convert the ln to log and combine all the constant together to and a simple equation: 

Simplified Form

COULOMBS AND AMPERES IN CURRENT

C= A x t 

C: Coulomb

A: Ampere 

t: second 

Note 1C= 1As

Source: Lectured by Professor Eric Bullock