Electrochemistry
By: Juan Mazzini and Liza
Cohen
Basic Info.
Formulas
• E = E◦
- (RT/ nF) ln(Q)
• ∆G = ∆G◦ + RT ln(Q)
• ∆G◦ = -nFE◦
Constants
• F= 96500 C/Mole e- (C= coulombs)
• R= 8.314 J*mol-1*K-1
Ideas for Red-Ox
reactions
• OXIDATION  Loss of Electrons
• REDUCTION  Gain of
Electrons
• ** Reducing Agent = Substance
being oxidized
• ** Oxidizing Agent = Substance
being reduced
Procedures for
balancing RXN
• **Remember (charges)  F= -1,
O= -2, H= 1+ (except when
hydride), pure elements = 0.
• -Write properly balanced half
reactions and get e- to cancel out.
•
- in acidic solution, add H+ and
H2O
•
- in basic solution, do likewise.
However, after balanced, add OH’s
to form H2O’s.
Sample Problems
What is the oxidation state of
each atom?
• H2O
• AsO4• Cr2O72-
Sample Problem
CH4 + O2  CO2 + H2O (unbalanced)
• a. Determine which atom is oxidized
and which is reduced.
• b. Given that the cell reaction takes
place in acidic solution,
•
i. write the two balanced half
reactions that occur as the cell
operates
•
ii. combine the two half reactions
into an overall balanced reaction
Electricity
• -Reaction with greater potential is reduced.
• -Reaction with smaller potential is flipped
around (potential changes sign).
•
**Do not multiply by moles Voltage is
independent of moles.
• - E◦cell= E◦ox + E◦red
• -Anode- substance being oxidized. Cathodesubstance being reduced. (vowels with
vowels)
• -e- flow from anode to cathode
• -ions flow from cathode to anode
• -oxidized: mass decreases
• -reduced: mass increases
From: www.sparknotes.com
Sample Questions
•
•
•
•
Mass increase/decrease?
Direction of e-/ion flow?
Location of anode/cathode?
Determining the voltage
Current
• I = charge/ time = q/t
• E= joules/ coulomb = J/C
WHIN? (What Help is Needed)
© Mr. John Charles Bruss