Electrochemistry (cont.) Chem 1220(Chemistry, Dr. Clark, General Chemistry)
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Chem 1220(Chemistry, Dr. Clark, General Chemistry)
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This 3 page Class Notes was uploaded by Phillip Fishbein on Friday April 15, 2016. The Class Notes belongs to Chem 1220(Chemistry, Dr. Clark, General Chemistry) at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by Dr. Clark in Winter 2016. Since its upload, it has received 8 views. For similar materials see General Chemistry in Chemistry at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months.
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Date Created: 04/15/16
Voltaic (Galvanic) Cells o Two nodes in solutions connected by wire/voltmeter Solutions contain ions of the respective nodes Solutions connected by “salt bridge” o Reduction occurs at the CATHODE Solution contains ion form of cathode Gains mass from solution o Oxidation occurs at the ANODE Solution contains ion form of anode Loses mass to solution o Electrons flow from anode through the wire to the cathode o Electric Potential Ecell E ocathodeEoanode Volts Get values from standard reduction table No flipping of sign or multiplying by coefficients Standard Reduction Potential is an intensive property o Cell Notation Anode | Anode solution ([M]) || Cathode solution ([M]) | Cathode o Salt Bridge Soluble salt in bridge between solutions Positive ion moves to cathode solution as reaction progresses Negative ion moves to anode solution as reaction progresses o Voltaic/Galvanic Cells, when connected, move electrons spontaneously o Standard Hydrogen Electrode Usually a reference electrode Test tube with H (g) at 1 atm and platinum wire 2 Can act as cathode or anode pH of solution changes as reaction progresses o Relating Standard Cell Potential, Standard Free Energy Change, and Equilibrium Constant o Positive E iodicates spontaneous process Negative E indicates nonspontaneous process V∗mole −¿ mole =96485 J ¿ o o ' C ∆ G =−nFE ;F=Farada y sconstant=96485 ¿ o ∆ G =−RT lnK (provided onexam) o RT E = nF lnK(not provided onexam) n in these equations is the # of electrons transferred in the balanced equation Derivation of last equation Substitute left side of equation 1 with right side of equation 2 o Solve for E o Non-Standard Conditions Nernst Equation E=E −o RT lnQ(providedonexam) nF Q changes as the cell operates E changes as the cell operates E = 0 at equilibrium o Q = K o Can be used to find equation 3 above Increasing concentration of the anode solution increases E Increasing concentration of the cathode solution decreases E Increasing mass of solid does not affect E o Cell Potential and Current Potential difference between anode and cathode called electromotive force (emf) Measured in Volts o Volts = Joules / Coulombs (J/C) Current is measured in amperes Amperes = Coulombs / second (C/s) Rate of electric flow Can run current through molten solutions of salts to isolate the elements Discovery of Alkali and Alkaline Earth Metals Electrolysis (Electrolytic Cell) Adding electrons to a solution Has negative cell potential o Work has to be applied to make the reaction occur o Voltage applied to cell must be greater than the magnitude of the cell potential for the reaction to occur Electroplating o Both electrodes in same solution connected to a battery o Used to plate cathode with anode o Forces electrons to leave anode and enter the cathode o Opposite logic as Galvanic Cell o Solution should match the anode o Cathode and Anode determined by how they are connected o Used to protect materials such as iron Zinc is easier to oxidize than iron, so covers iron with zinc to protect it from oxidizing Cover with silver to keep it from oxidizing Silver resists oxidation because it is more favorable to be in solid form