18.1 Galvanic Cells

• Galvanic (voltaic) cell: Device in which chemical energy is changed into electrical energy
• What does a Galvanic cell use?

  Spontaneous redox reactions to produce a current that can be used to do work.
• Where does Galvanic (voltaic) cell reaction occur?

  At the interface between the electrode and the solution where electron transfer is facilitated; makes batteries for many uses
• Electrolytic cell: Devise that uses an external source of electrical energy in a non-spontaneous redox reaction to produce a chemical change. EX: Process of electrolysis; metal plating and other uses
• What are the two compartments of a Galvanic cell?

  Anode (Oxidation); Cathode (reduction)
• A bridge between the compartments allowing a charge balance:

  1. Salt Bridge: contains a strong electrolyte in a U-tube that permits ions to flow without extensive mixing of solutions
  2. Porous disk: Contains tiny passages that allow a hindered flow of ions
• There is also an electrical wire connecting the two compartments completing the circuit [ in a Galvanic cell]
• Anode: electrode compartment where oxidation occurs
• Cathode: electrode compartment where reduction occurs
• Cell potential (Ecell): Pull of driving force on electrons; also known as the electromotive force - emf- of the cell
• Volt (V): a unit of electrical potential, often defined as J/C (potential energy/ Charge)
• Voltmeter: draws current through a known resistance
• Maximum cell potential can be ascertained by measuring it under zero current.
• Potentiometer: variable voltage device, which is powered by an external source, inserted in opposition to the cell potential
• Standard reduction potential (E⁰ ): Table of potentials written as a reduction half-reaction under standard conditions/
• The most positive E⁰ : the easiest to reduce (oxidizing agent)

  1. The strongest oxidizing agent will have the most positive E⁰
• The most negative E⁰ : the easiest to oxidize (reducing agent)

  1. The strongest reducing agent will have the most negative E⁰
• Electrons flow from the anode to the cathode
• In which direction will anions flow relative to the salt bridge?

  From the cathode compartment into the salt bridge
• Electrons on products (right side) its an oxidation reaction
• Electrons on reactants (left side) is reduction