CONTENT OBJECTIVE
WHAT THE HECK DO I NEED TO BE ABLE TO DO?
I can make qualitative or quantitative
predictions about galvanic (voltaic) cells
based on half-cell reactions and potentials
and analyze these cells to identify
properties of the underlying redox
reactions.
Galvanic/Voltaic Cells
1. In Pre-AP Chemistry, we deal mostly
with reactions that are spontaneous—
meaning, they will happen on their own if
all the “ingredients” are present.
Electrochemistry
2. Galvanic cells use
thermodynamicallyfavored (spontaneous)
REDOX reactions to
produce electrical
energy via a flow of
electrons (also known
as Voltaic cells or
batteries).
a. In short: galvanic
(voltaic) cells produce
current!
Electrochemistry
Galvanic/Voltaic Cells
3. To use that current,
we need to separate
the place where
oxidation is occurring
from the place where
reduction is occurring.
Electrochemistry
Galvanic/Voltaic Cells
• QUICK REMINDERS*
1) Oxidation is LOSS of electrons
OIL (LEO)
Ex: Zn (s)  Zn2+ (aq) + 2e2) Reduction is GAIN of electrons
RIG (GER)
Ex: Cu2+ (aq) + 2e-  Cu(s)
Electrochemistry
Galvanic/Voltaic Cells
B. Parts of the Galvanic Cell
1. Electron flow: ALWAYS through the
wire from anode to cathode (alpha order)
Electrochemistry
Galvanic/Voltaic Cells
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
Electrochemistry
Galvanic/Voltaic Cells
B. Parts of the Galvanic Cell
Say you have 2 solutions and you’re
trying to make a galvanic cell:
Zinc sulfate = ZnSO4(aq)
Copper (III) sulfate Cu2(SO4)3
Ex: Zn (s)  Zn2+ (aq) + 2eEx: Cu2+ (aq) + 2e-  Cu(s)
Electrochemistry
Galvanic/Voltaic Cells
B. Parts of the Galvanic Cell
2. anode (–): the electrode where
oxidation occurs (may appear smaller over
time)
Oxidation: Zn (s)  Zn2+ (aq) + 2e-
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
Zinc anode
(electrode)
Zinc sulfate
solution (oxidation)
Electrochemistry
Galvanic/Voltaic Cells
B. Parts of the Galvanic Cell
3. cathode (+) : the electrode where
reduction occurs (may appear larger over
time)
Reduction: Cu2+ (aq) + 2e-  Cu(s)
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
Zinc anode
(electrode)
Zinc sulfate
solution (oxidation)
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
Zinc anode
(electrode)
Zinc sulfate
solution (oxidation)
Copper cathode
(electrode)
Copper sulfate
solution
(reduction)
Electrochemistry
Galvanic/Voltaic Cells
B. Parts of the Galvanic Cell
4. Salt bridge or (disk): bridge between
cells whose purpose is to provide ions to
balance the charge
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
Zinc anode
(electrode)
Zinc sulfate
solution (oxidation)
Copper cathode
(electrode)
Copper sulfate
solution
(reduction)
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
salt bridge
Zinc anode
(electrode)
Zinc sulfate
solution (oxidation)
Copper cathode
(electrode)
Copper sulfate
solution
(reduction)
Electrochemistry
Galvanic/Voltaic Cells
B. Parts of the Galvanic Cell
5. Voltmeter: measures the cell potential
(emf or E°) in volts
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
salt bridge
Zinc anode
(electrode)
Zinc sulfate
solution (oxidation)
Copper cathode
(electrode)
Copper sulfate
solution
(reduction)
Electrochemistry
Galvanic/Voltaic Cells
Electron (-) flow
voltmeter
salt bridge
Zinc anode
(electrode)
Zinc sulfate
solution (oxidation)
Copper cathode
(electrode)
Copper sulfate
solution
(reduction)
Electrochemistry
Voltaic Cells
A typical cell all labeled looks like this.
Electrochemistry
C. Terms to remember through shortcuts
• ca+hode: the cathode is + in
galvanic/voltaic cells, and so the anode is
negative (-)
Electrochemistry
C. Terms to remember through shortcuts
• AN OX: oxidation occurs at the anode
(may show mass decrease)
• RED CAT: reduction occurs at the
cathode (may show mass increase)
(Combine that with remembering
OIL RIG / LEO GER !)
Anode = oxidation; oxidation is loss
Reduction = cathode; reduction is gain
Electrochemistry
C. Terms to remember through shortcuts
• FAT CAT: electrons in a
voltaic/galvanic cell
ALWAYS flow
From the Anode To the
CAThode
And the cat gets fat!
(cathode gains mass over
time)
“ANODE”-rexic! (anode
loses mass over time)
Electrochemistry
D. Standard Reduction Potential for
a Galvanic/Voltaic Cell (E°)
° cell, the metal
1. In a galvanic (voltaic)
with the greater (more positive) reduction
potential will be reduced!
Electrochemistry
D. Standard Reduction Potential for
a Galvanic/Voltaic Cell (E°)
° come from a chart
2. Because the values
of standard reduction potentials, you
MUST REVERSE the sign of the E°of
the oxidized species before adding to
the E° of the reduced species.
Electrochemistry
D. Standard Reduction Potential for
a Galvanic/Voltaic Cell (E°)
3. How to calculate °
the cell potential of a
galvanic cell:
Eoox = - Eored and
Eocell = Eooxidation + Eoreduction
Electrochemistry
D. Standard Reduction Potential for
a Galvanic/Voltaic Cell (E°)
°oxidation-reduction
4. For a spontaneous
(voltaic/galvanic cell) to occur, the overall
cell potential must be positive.
Electrochemistry
• Example: Consider the half reactions
shown below and the standard electrode
reduction potentials that follow.
Cu2+(aq) + 2 e-  Cu(s)
Zn2+(aq) + 2 e-  Zn(s)
Eo = +0.34 V
Eo = -0.76 V
Electrochemistry
Cu2+(aq) + 2 e-  Cu(s)
Zn2+(aq) + 2 e-  Zn(s)
Eo = +0.34 V
Eo = -0.76 V
Which one has the GREATER (more positive)
reduction potential?
Cu2+ or
Zn2+
(If it has the GREATER reduction potential, Eo,
it has a greater desire for electrons and will be
reduced!!!!)
Electrochemistry
Cu2+(aq) + 2 e-  Cu(s)
Zn2+(aq) + 2 e-  Zn(s)
Eo = +0.34 V
Eo = -0.76 V
Which one has the GREATER (more positive)
reduction potential?
Cu2+ or
Zn2+
(If it has the GREATER reduction potential, Eo,
it has a greater desire for electrons and will be
reduced!!!!)
Electrochemistry
Keep the equation the same since it’s
being reduced:
Cu2+(aq) + 2 e-  Cu(s)
Therefore: Eored = +0.34 V
Electrochemistry
Zn2+(aq) + 2 e-  Zn(s)
Eo = -0.76 V
Zinc has the LOWER reduction potential (Eo),
so it will be oxidized. (Flip the sign of the Eo!)
Flip the equation since it is being oxidized:
Zn (s)  Zn2+(aq) + 2eTherefore: Eoox = - Eored
-(-0.76 V) = +0.76 V
Electrochemistry
Now calculate Eocell by plugging in the
numbers:
Eocell = Eoox + Eored
= 0.34 + 0.76
= +1.10 V
****Galvanic (Voltaic) cells
should ALWAYS have a positive
o
E cell value!!!!!!!!!!!!!****
Electrochemistry
Take your half reactions, balance, and find the
net ionic equation.
Half reactions:
Cu2+(aq) + 2 e-  Cu(s)
Zn (s)  Zn2+(aq) + 2eNet ionic equation:
Cu2+(aq) + Zn(s)  Zn2+(aq) + Cu(s)
Electrochemistry