Chapter 11.1: Galvanic Cells

• Electrochemistry: a study of the processes involved in converting chemical energy to electrical energy, vice versa Electric current: the flow of electrons in a circuitredox reactions involve the transfer of electrons from one reactant to another

• Galvanic cell/Voltaic cell: a device that converts chemical energy to electrical energy prevents reactants in redox reaction from coming into direct contact with one another External circuit: circuit outside the reaction vessel where electrons flow from one reactant to the other Known as the electric current Porous barrier/semi-permeable membrane: separates two half-cells Electrodes: conductors that carry electrons into and out of a cell electrolytes: substances that conduct electricity when dissolved in water Anode: electrode at which oxidation occursElectrons are released by oxidationCathode: electrode at which reduction occurs Electrons flow through external circuit from negative electrode to positive electrode External circuit conducts electrons from the anode to cathode of a galvanic cell Salt bridge: contains an electrolyte solution that does not interfere in the reactionPorous plug at the ends of the salt bridge: allows ion migration to maintain electrical neutrality In shorthand representation, anode is shown on left and cathode on the right vertical line ” | “ represents phase boundary between electrode and the solution of the half cell Double vertical lines “ || “ represent salt bridge/porous barrier Ex. Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s) Spectator ions omitted Inert electrodes: electrode made from a material that shows neither a reactant nor a product of the cell reaction Ex. a platinum electrode is chemically unchanged but included in shorthand representation

• Electric potential, E: the difference between potential energy at the anode and the potential energy at the cathode Measured in volt (V)Electric potential is more commonly known as cell voltage Another name for it is cell potential can be measured using an electrical device called a voltmeter.

• Dry Cell Battery:

  • Dry cell: galvanic cell with electrolytes contained in a paste thickened with starchModern contain electrolyte paste

  • Battery: a set of galvanic cells connected in series

  • The negative electrode of one cell is connected to the positive electrode of the next cell in the set

  • The voltage of a set of cells connected in series is the sum of the voltages of the individual cells

  • Primary battery: disposable batteries that run out of reactant

  • Secondary battery: a rechargeable battery

Chapter 11.2 Standard Cell Potentials

• Reduction potential: half-cell potential for a reduction half-reaction

• Standard reduction potentials are only used when ions and molecules are in their standard states (1 atm, 25 ̊C, aqueous, and ions at 1mol/L)

  • E ̊: standard reduction potentials at standard states

  • Method 1: E ̊ cell = E ̊ cathode − E ̊ anode

  • Standard cell potentials of all galvanic cells have positive values

  • Oxidation potential: half-cell potential for an oxidation half-reaction

  • Method 2: E ̊ cell = E ̊ reduction − E ̊ oxidation

  • Both methods 1 and 2 are equivalent in finding cell potential

Chapter 11.3 Electrolytic Cells

• Electrolytic cell: device that converts electrical energy to chemical energy. Lower potential energy to higher potential energy Uses the process of electrolysis: non-spontaneous and requires energy to occur. Requires electrodes, one electrolyte, external circuit (the main difference between galvanic cell)Some have a salt bridge / porous barrier External source of electricity forces electrons onto one electrode, causes electrode to become negative relative to another electrode Ex. positive ions move towards the negative electrode which gains electrons and are reduced Reduction occurs at the cathode, and oxidation occurs at the anode of an electrolytic cell (same as galvanic cell)

• All electrolytic cells have negative cell potentials

• Overvoltage: excess voltage required above the calculated value

  • Depend on the gases involved and on the materials in the electrodes

• Electroplating: process in which a metal is deposited, or plated, onto a cathode in an electrolytic cell

• Common secondary batteries found in car engines

  • The generator of the car recharges the battery

Chapter 11.4: Faraday’s Law

• Michael Faraday (1791-1867): connected concepts of stoichiometry and electrochemistry

• Electrical current: the flow of electrons through an external circuit

  • Measured in ampere (A)

• Quantity of electricity/electrical charge: product of the current flowing through circuit and time for which it flows

  • Measured in coulomb (C)

• Relationship between coulomb and ampere

  • charge (in coulombs) = current (in amperes) x time (in seconds)

    • one coulomb is the quantity of electricity that flows through a circuit in one second if the current is one ampere

• Need to know the electrical charge on a mole of electrons for stoichiometric calculations

  • Charge on one mole of electrons

    • Measured as one faraday (1 F)

• Faraday’s Law: states that the amount of a substance produced or consumed in an electrolysis reaction is directly proportional to the quantity of electricity that flows through the circuit

• Extraction: the process by which metals are obtained from an ore

  • Process of electrolytic cells

  • Refining: the process of purifying a material

Chapter 11.5: Issues Involving Electrochemistry

• Corrosion: spontaneous redox reaction of materials with substances in their environment

  • Oxygen is a common oxidizing agent

  • Some corrosion can be a hazard

    • Rust is hydrated iron (III) oxide

• Galvanizing: a process in which iron is covered with a protective layer of zinc

  • Zinc acts as a protective layer

• Sacrificial anode: easily destroyed layer that is meant to be corrosive to protect another metal from corroding

• Cathodic protection: another method of preventing rusting, a more reactive metal is attached to the iron object

  • Destroyed slowly by oxidation but replaced less than sacrificial anode

• Fuel cell: battery that produces electricity while reactants are supplied continuously from an external source

  • reactants continuously flow into the cell, a fuel cell is also known as a flow battery.

  • fuel supply in a fuel cell is unlimited

  • alkaline fuel cell: half-reactions do not include solid conductors of electrons, instead has two inert electrodes

  • Hydrogen fuel cell: more effective in converting 80% chemical energy to fuel energy; however hydrogen is not naturally found

• Chlor-alkali process: brine (NaCl) is electrolyzed in a cell

  • Used to destroy bacteria in water

  • Brine: saturated solution of sodium chloride