I Chapter 20 Electrochemistry Electrochemistry the study of the relationship between electricity and chemical reactions A 20 1 Oxidation States and Oxidation Reduction Reactions Oxidation states oxidation numbers Oxidizing agent or oxidant the substance that makes it possible for another substance to be oxidized itself becomes reduced Reducing agent or reductant a substance that gives up electrons becomes oxidized thereby causing another substance to become reduced gains electrons B 20 2 Balancing Redox Equations Half reactions breaking the full reaction into the oxidation part and the reduction part Balancing equations by the Method of Half Reactions o 1 Divide reaction into half reactions o 2 Balance the half reactions First by balancing the elements that are not H or O Second balance Os by adding H20 as needed Third balance the H atoms by adding H as needed Fourth balance the overall charge by adding electrons as needed o 3 Multiply half reaction by integers as need to make the number of electrons lost and electrons gain equal for both half reactions o 4 Add half reactions together and simplify if possible o DOUBLE CHECK ALL THAT SHIT Cuz you can easily mess up with all those steps o Also if you are doing this in a basic solution you need to add OH in to neutralize H Then make sure to form H20 if you can don t leave the components separate 20 3 Voltaic Cells C Voltaic or galvanic cells a device in which the transfer of electrons takes place through an external pathway rather than direction between reactants present in the same reaction vessel Voltaic cells are spontaneous Anode the electrode at which oxidation occurs Cathode the electrode at which reduction occurs Anions always migrate toward the anode and cations toward the cathode Electrons flow from anode through an external circuit to cathode 20 4 Cell Potentials under Standard Conditions D Cell potential the difference between the two electrodes of a voltaic cell Electromotive force driving force that pushes electrons through the external circuit Standard conditions 25 degrees C I molar at 1atm Standard cell potential cell potential at standard conditions Standard reduction potentials the standard reduction potential of the cathode minus the standard reduction potential of the anode Also equal to standard cell potential Whenever we assign an electrical potential to a half reaction we write the reaction as a reduction Changing the stoichiometric coefficient in a half reaction does not affect the value of the standard reduction potential This really just means this is an intensive property The more positive the standard reduction potential is the greater the tendency for reduction under standard conditions This really just means the substance is better oxidizing agent The half reaction with the most negative reduction potential is the one most easily reversed and run as an oxidation E 20 5 Free Energy and Redox Reactions A positive value of E indicates a spontaneous process a negative value of E indicated a non spontaneous one Faraday s constant F 96485C mol F 20 6 Cell Potentials under Nonstandard Conditions Use equations given G G RTlnQ E E 0592 n logQ When n is electrons received on the right side of the equation 20 9 Electrolysis G Electrolytic reactions are non spontaneous Electrolytic cell basically everything is the same except the charges at the anodes are switched o So anode would have a positive charge cathode would have negative charge