Regents Warm-Up

1
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.

2
Electrochemistry

• AIM What is a Voltaic Cell?
• Do Now
• In the rxn
• 2Mg O2? 2MgO
• What is oxidized what is reduced?

3
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 Cu2? Zn2 Cu0
• This is a spontaneous rxn
• What is oxidized what is reduced?
• There are 2 types of electrochemical cells

4
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

• Whats an everyday example of a voltaic cell?
• Batteries are voltaic cells

5
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

6
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

7
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

8
Voltaic Cell

• In a battery the anode is the negative terminal
• The cathode is the positive terminal
• Why does a battery die?

9
Voltaic cells

• After awhile the redox reaction come to
  equilibrium and the cell(battery) no longer
  operates

10
Voltaic Cells

• Cathode ?Reduction
• (both start w/consonants)
• Anode ? Oxidation
• (both start w/ vowels)

11
Voltaic Cells

• A voltaic cell spontaneously converts
• 1. electrical energy to chemical energy
• 2. electrical energy to nuclear energy
• 3. chemical energy to electrical energy
• 4. nuclear energy to electrical energy

• Which energy conversion occurs during the
  operation of a voltaic cell?
• 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.

12
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

13
Voltaic Cells

• Given the balanced equation representing the
  reaction occurring in a voltaic cellZn(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)