CH 302 1st Edition Lecture 24Outline of Last Lecture I. ElectrochemistryII. Redox ReactionsIII. Redox NumbersIV. Balancing Redox ReactionsOutline of Current Lecture I. Oxidation and ReductionII. Electrochemical CellsIII. Electrochemical Cell PartsIV. Cell Short HandCurrent LectureOxidation and Reduction:- If something is oxidized then its oxidation number goes up. Oxidation is the loss of electrons.- If something is reduced then its oxidation number goes down. Reduction is the gain of electrons.- Here are two pictures and ways to help you remember this. Pick one and remember it forever.1. LEO says GER Lose Electrons Oxidation. Gain Electrons Reduction.2. OIL RIG Oxidation Is Loss. Reduction Is GainElectrochemical Cells- In an electrochemical cell, we physically separate the oxidation and reduction chemistry in different "compartments". - The electrons from the oxidation are then run through an external circuit before being used in the reduction reaction. - As this is moving negative charge from one location to another, we need to compensate for this by moving other charges to balance this displacement of charge. - This is accomplished by using a salt bridge that allows the migration of spectator ions to balance the flow of electrons.- Each half of the electrochemical cell has an electrode to which the wire for our external circuit is connected. - The chemistry takes place at the surface of this electrode. The electrode on the oxidation side is called the anode. - The electrode on the reduction side is called the cathode. As a short hand, we simply refer to the two sides of the cell as the anode side and the cathode side.Electrochemical Cell Parts- In an electrochemical cell, we are running a redox reaction, but we have physically separated the oxidation and reduction reactions into different locations. - These take place in different "halves" of the cell.- We then connect the two halves of the cell with an external wire to allow for electron flow from one side to the other. - We also connect the two halves with a "salt bridge" to allow spectator ions to flow to counter balance the electron flow.- The oxidation and reduction reactions are now in different locations. - To allow the electrons to flow from the oxidation reaction (that is producing electrons) to the reduction reaction (that is consuming the electrons), we need to connect the two reactions electrically. - This is accomplished by using metal electrodes. These electrodes serve a the place where the chemistry is taking place. - Sometimes they are part of the reaction. Sometimes they are simply used as a means to"deliver/collect" the electrons. - The electrode in the oxidation reaction is call the anode. The electrode for the reductionreaction is called the cathode. The electrons flow from the anode to the cathode.Cell Short Hand- It becomes very cumbersome to draw a picture of an electrochemical cell each time you would like to discuss one.- As such, we have developed a short hand notation for a cell.- Rather than having this picture of the cell, we have a shorthand that is the same moving from left to right in our diagram.- We start with the anode which we write to the right of a "" symbol. In total, this will look like< Ni | Ni2+ || H+ | H2 | Pt >This is the most generic of notations. To be more specific we might include the concentrations (or pressures) along with the
View Full Document
Unlocking...