Download Electrochemisty

Electrochemisty
Galvanic or Voltaic cells
o
Electrolytic cells
Spontaneous reaction E cell +
These terms may be used in a question
about galvanic/voltaic cells…
Ecell ; reduction potential; oxidizing agent;
reducing agent; reduction; oxidation; anode;
cathode; salt bridge; electron flow; voltage;
cell potential; electromotive force;
galvanic/voltaic; electrode; battery;
Non spontaneous reaction Eo cell These terms may be used in a question
about electrolytic cells…
current; amps; time; grams (mass);
plate/deposit; electroplating; identity of
metal; coulombs of charge
Key Formulas and Relationships
ANOx – oxidation at the anode
Key Formulas and Relationships
96,500 Coulombs = 1 mole of electrons
RedCat – reduction at the cathode
molar mass = 1 mol.
FATCAT – e- from the anode to the cathode
# electron in eqn = # moles
(use balanced overall equation for ratio)
Convert all amps to # coulombs = 1 sec
LEO goes GER lose e- oxidation gain ereduction
“the LARGEST reduction potential gets to
be reduced”
# Coulombs = It or I=q/t (formula
sheet)
where I is amps
Ecell = Eox + Ered from table
0.0592
E cell = E table log Q n=# of en
Key Concepts and Important Phrases
The purpose of the salt bridge is to “provide
ions to keep the solutions in the cells from
becoming charged”
Be able to explain whether Ecell goes up or
down when concentrations change. Justify
using the Nernst equation relating the sign
of logQ to the increase or decrease in Ecell
smaller
(logQ – fhappens when
[
larger
reactant] . [product]
Label the parts of a galvanic cell:
Anode; cathode; salt bridge; electron flow;
half reactions; overall reaction; direction of
ions from salt bridge
Will the electrode be gaining mass or losing
mass as that half reaction occurs? Look at
equation to detemine
Key Concepts and Important Phrases
To predict products in an aqueous solution:
Usually group IA or IIA metal will not be
reduced USE WATER
LAGER Eo RED is Reduced
No polyatomic ion will ever oxidize USE
WATER
KNOW THESE:
Red: 2H2O + 2e-  H2 + 2OHOx: 2H2O  O2 + 4H+ + 4e-
Inert Pt electrodes are used in reactions from
ion to ion (ie Fe3+  Fe2+) or gases
Connections to Other Chapters
Thermo: G = -nFE
Connections to Other Chapters
Stoichiometry through mole:mole ratio of
coefficients and/or molar masses
Assigning oxidation numbers and balancing
redox reactions
at equilibrium E = 0 and Q = K
0.0592
E0 
log K
n
Potential Pitfalls and Unit warnings
Watch signs on voltages --LARGEST
reduction potential is used as is and the
OTHER one is reversed and changed sign
When balancing overall reaction make sure
# of electrons is the same in both half
reactions.
Oxidizing agent is reduced (always a
reactant – use formula as written in
equation)
Reducing agent is oxidized Eo cell (always a
reactant – use formula as written in
equation)
Units on Eare volts J/coulomb
Potential Pitfalls and Unit warnings
Watch to make sure units cancel out in
your calculations. Be careful to label
moles as moles of e- or moles of A etc. to
avoid confusion.