Regents Warm-Up
Given the balanced equation representing a
reaction:
Cl2(g) Cl(g) + Cl(g)
What occurs during this change?
(1) Energy is absorbed and a bond is broken.
(2) Energy is absorbed and a bond is formed.
(3) Energy is released and a bond is broken.
(4) Energy is released and a bond is formed.
Electrochemistry
AIM: What is a Voltaic
Cell?
Do Now:
In the rxn:
2Mg + O2 2MgO
What is oxidized & what
is reduced?
Electrochemistry
• Electrochemistry: is
the study of the
relationship between
electrical energy and
chemical reactions
• In redox reactions
electrons are
transferred between 2
atoms
Example
Zn0 + Cu+2 Zn+2 + Cu0
• This is a spontaneous
rxn
• What is oxidized &
what is reduced?
• There are 2 types of
electrochemical cells
Voltaic Cell
• Voltaic Cell: uses a
spontaneous redox
reaction to provide a
source of electricity
• Oxidation-Reduction half
reactions take place in
different containers called
half cells
• Half-cells are connected
by what is called a salt
bridge
• What’s an everyday
example of a voltaic
cell?
• Batteries are voltaic
cells
Voltaic Cell
• Oxidation occurs in the
left half-cell
• This is where electrons are
lost
• They travel through the
connected electrodes into
the reduction half cell
• This flow of electrons is
electricity
Voltaic Cell
• The solid metal strips are
called electrodes
• The electrode where
OXIDATION takes place is
the ANODE
• The electrode where
REDUCTION takes place is
the CATHODE
• Electrons ALWAYS flow from
the anode to the cathode
Voltaic Cell
• There will be a
connection between the 2
half-cells where ions can
flow to balance the flow
of electrons
• If the wire connecting the
electrodes is connected to
an external circuit, the
cell is a source of
electrical energy
Voltaic Cell
• In a battery the anode is
the negative terminal
• The cathode is the
positive terminal
Why does a battery “die”?
Voltaic cells
• After awhile the redox
reaction come to
equilibrium and the
cell(battery) no longer
operates
Voltaic Cells
• Cathode Reduction
(both start w/consonants)
• Anode  Oxidation
(both start w/ vowels)
Voltaic Cells
A voltaic cell spontaneously
converts
Which energy conversion occurs during
the operation of a voltaic cell?
1. electrical energy to
chemical energy
2. electrical energy to nuclear
energy
3. chemical energy to
electrical energy
4. nuclear energy to electrical
energy
1. Chemical energy is spontaneously
converted to electrical energy.
2. Electrical energy is spontaneously
converted to chemical energy.
3. Chemical energy is converted to
electrical energy only when an
external power source is provided.
4. Electrical energy is converted to
chemical energy only when an
external power source is provided.
Voltaic Cells
What is the purpose of the
salt bridge in a voltaic
cell?
1. It blocks the flow of
electrons.
2. It is a path for the flow of
electrons.
3. It blocks the flow of
positive and negative ions.
4. It is a path for the flow of
positive and negative ions.
In a voltaic cell, chemical
energy is converted to
1. electrical energy,
spontaneously
2. nuclear energy,
spontaneously
3. electrical energy,
nonspontaneously
4. nuclear energy,
nonspontaneously
Voltaic Cells
Given the balanced equation representing the reaction
occurring in a voltaic cell:
Zn(s) + Pb2+(aq) → Zn2+(aq) + Pb(s)
In the completed external circuit, the electrons flow from
1. Pb(s) to Zn(s)
2. Zn(s) to Pb(s)
3. Pb2+(aq) to Zn2+(aq)
4. Zn2+(aq) to Pb2+(aq)