Electrochemistry: Basic Concepts
Sometimes, you must find a balanced reaction of
cells from only reduction half-reactions.
We will go through steps to follow and examples
Electrochemistry: Basic Concepts
Equations of Cells
• Standard Reduction Potentials: lists which
are more likely to reduce (take electrons)
reduced
Cu2+ + 2e- → Cu
Cu2+ | Cu
• When comparing standard reduction
potentials in a cell, the ½ reaction that is…
• more (+) is reduction
• more (-) is oxidation
Electrochemistry: Basic Concepts
Equations of Cells
• So… which is more likely to reduce?
1) Li+|Li or Be2+|Ba
2) Ga3+|Ga or Cr2+|Cr
3) Cr3+|Cr2+ or Cr2+|Cr
4) Cl2|2Cl- or Cu+|Cu
5) Ag+|Ag or Rb+|Rb
6) Mn2+|Mn or Au+|Au
To write equations of Cells
1) Identify which reaction is oxidation and which is
reduction, 2) write the balanced equation
Silver in a solution of Ag+ and Nickel in a solution of Ni2+
Ag+(aq) + e- → Ag(s) EºAg+|Ag = +0.800 V reduction
Ni2+ + 2e- → Ni(s)
EºNi2+|Ni = -0.257 V
Ni(s)
→ Ni2+ + 2e2 Ag+(aq) + 2 e- → 2 Ag(s)
Ni(s) + 2Ag+(aq) → Ni2+ + 2Ag(s)
oxidation
1) Identify which reaction is oxidation and which is
reduction, 2) write the balanced equation
Magnesium in a solution of Mg2+ and Lead in a solution of Pb2+
Mg2+(aq) + 2e- → Mg(s)
EºMg2+|Mg = -2.372 V
ox
Pb2+(aq) + 2e- → Pb(s)
EºPb2+|Pb = -0.126 V
red
Mg(s)
→ Mg2+(aq) + 2ePb2+(aq) + 2e- → Pb(s)
Mg(s) + Pb2+ → Mg2+(aq) + Pb(s)
1) Identify which reaction is oxidation and which is
reduction, 2) write the balanced equation
Beryllium in a Be2+ solution and Iridium in a Ir3+ solution
Be2+(aq) + 2e- → Be(s)
EºBe2+|Be = -1.847 V
ox
Ir3+(aq) + 3e- → Ir(s)
EºIr3+|Ir = +1.156 V
red
3 Be(s)
→ 3 Be2+(aq) + 2e
6e-2 Ir3+(aq) + 6e
3e-- → 2 Ir(s)
3Be(s) + 2Ir3+(aq) → 3Br2+(aq) + 2Ir(s)
Then, how
would you
find the cell
potential?
Eºcell = Eºred - Eºox
Reminders:
• Ch 21 Practice Problems
o You know how to do the entire worksheet
o SHOW ALL WORK! No work, no credit.
o The entire thing is due Monday at the
beginning of class
• WA ch 21: due Monday night
o Use my website and the book for hints
Fin jour 3
Table of Contents
Chapter 21: Electrochemistry
21.2 – Types of Batteries
21.3 – Electrolysis
In class we will cover only what you need
to know for the test. Please use your book
to answer questions for WebAssign.
Electrochemistry: Basic Concepts
21.2: Batteries
• Alessandro Volta:
• If one cell generates a current, several
cells should make a larger current
• He piled several cells together to make the
first battery
• Battery: one or more electrochemical cells in
a single package
21.3: Electrolysis
• Electrolysis: using electric energy to cause a
chemical reaction.
• Electrolytic cell: An electrochemical cell in
which electrolysis occurs.
• Electrolysis forces a current in the reverse
direction (a nonspontaneous reaction) by passing
an electric current through it (recharging)
Electrochemistry: Basic Concepts
Voltaic Cell
e-
e-
Electrolytic Cell
e-
Voltage
source
e-
An electrolytic cell is just the opposite of a voltaic cell
Electroplating
Reduction of silver ions onto cheaper metals forms
silverplate.