Unit 10: Electrochemistry Content Outline: Voltaic Cells (10.2)

I. Voltaic Cells (Batteries) A. These batteries use a spontaneous redox reaction to convert chemical energy into electrical energy (flowing electrons). B. The electrons are released, by a metal (Oxidation) at the Anode of the battery. Think about the periodic table and metal properties for families. 1. The electrons then travel through a “circular” path (circuit), where work is performed by a device, before returning to the battery. 2. The electrons flow through wires that are connecting the device with the battery. C. The electrons are received by the battery at the Cathode. Think receiving the “electric cat”. 1. The electrons are then combined with a metal (reduction). Remember, if a word ends in “tion” it is a process. Cathode and Anode are not processes but places on a battery. You must play close attention to wording when talking about batteries and electron flow. D. Three major types of Voltaic batteries exist: 1. Dry Cell a. This is a battery like you can buy in Wal-mart or a grocery store. b. It uses two dry metals separated by a membrane inside the battery. c. An electrochemical concentration gradient exists between the two metals, think diffusion as the electrons flow through the wire and device back to the battery. For example: Duracell or Energizer 2. Wet Cell a. This is a battery like found in cars and trucks. b. The metals are submerged in liquids to help circulate electrons. c. These tend to be very heavy, as most contain the metal lead. 3. Fuel Cell 4. This battery has reactants being pumped in and products pumped out continuously. a. Like a solar panel as water pumped in and water. b. The reactants, usually Hydrogen for powering motors, are constantly pumped into the reaction chamber. c. Oxygen is also pumped into the reaction chamber. d. The two ignite, producing energy, and create water vapor (product), which is released to the environment. e. This battery can theoretically operate forever, if reactants are provided and product is removed.

II. Electrical Potential A. This term refers to the “pull” on electrons as they move through the circuit. 1. The oxidizing agent (metal) at the cathode “pulls” the electrons. Think COP. 2. The reducing agent (metal) “pushes” at the anode. Think RAP. 3. RAP COP…as they must always go together (law of Conservation of Matter). 4. Electric Potential is expressed in Volts (V). a. The potential energy per unit charge. 5. Current a. Expressed in Amperes (A) OR AMPs. b. Used to describe the ease of movement for electrons through the circuit. c. The electrons flow from high electrical Potential to low electrical potential, just like diffusion.

III. Standard Electrode Potential (EO) A. This term helps to define how electrons move through a circuit and also relates the capacity of different metals to either donate or accept electrons. B. Reduction Potential (Reduction = gain) 1. This half reaction is shown as: metal ion + electrons  metal. For example: Zn2+ + 2e-  Zn C. Oxidation Potential (Oxidation = loss) 1. This half reaction is shown as Metal  metal ion + electron For example: Au  Au3+ + 3e- D. Solving Electrode Potential Problems: 1. Step 1: You need an Electrode Potential Table for finding E0 values. 2. Step 2: Mathematically expressed as: O O O O E CELL = E CATH – E ANAD OR E Cell = COP – RAP. 3. Step 3: Identify the two metals half reactions in your battery. 4. Step 4: Determine which is Cathode and which is anode.  Lowest value is the anode; higher is the cathode. Cat wins always.  You might have to reverse a reaction from your table. 5. Step 5: Combine into one equation. 6. Step 6: Balance electrons. 7. Step 7: Calculate using the above formula  The act of balancing the number of electrons DOES NOT affect the EO value.  Voltaic Batteries have positive Eo values. The highest value the better the battery.