Ch 20 Calculating Cell Voltage V5

Added: 2026-05-16

[00:00:00]Oh today's lesson we're going to go over how to calculate cell potential under standard collisions so the previous lecture we even over a galvanic cell which is an apparatus that [Music] makes use of a spontaneous redox reaction to generate electricity to move electrons around and so we need to know what is the voltage for that just like when you buy a battery galvanic cell is basically a battery tells you the voltage which is the electrical potential difference between the anode and the cathode and we'll go over that in a few minutes as well so to calculate the cell potential under standard conditions which we call a standard cell and standard condition means you have both reactants and products present if there are solids they are pure if they're liquids are pure if there are gases there are partial pressure is one atmosphere if there are aqueous their concentrations are more but they both are present and temperatures 25 degree Celsius so that also cool means that they're States so to calculate e cell under standard States we take the potential for the reduction half-reaction which is what happens at the Kappa plus the potential for the oxidation half-reaction which is what happens at the anode I like this formula better but some books I think including your book uses this form love it says ear induction cathode - II reduction and so it uses your doctrine potential proposal but I think if you use this one it makes more sense and you'll see a few minutes for guys so in order to get those values while we go to the reduction potential table remember when we went over oxidation this table quantifies the reduction in terms of reduction potential and reduction is the tendency to want to grab electrons so for example the tendency of fluorine gas to grab electrons and become fluoride ion is plus two point eight seven months or for chlorine it's plus one point three seven volts now these potentials are relative it's not absolute so it's just like height which is relative so sea level is our reference point and it's zero anything above sea level has positive height that passed in eyes for example 404 above sea level anything below sea level has negative height the depth values 200 feet below sea level and so for this table we set the tendency of hydrogen ion to want to grab electrons under standard space to be equal to zero and then we compared a tendency of everything else relative to hydrogen so when we say that the tendency of copper ion to want to grab electrons under standard States is plus point 337 that's relative to hydrogen so relative to hydrogen on copper two and wants to grab electrons more eager on the other hand zinc ion is negative point seven six - which means comfort - hydrogen on zinc oil in solution wants to grab electrons less it's kind of like the death values below sea level where the copper twine is above so the standard hydrogen electrode is what we compare everything else to and a standard hydrogen electrode is simply this half cell s HD stands for standard hydrogen electrode so you have hydrogen ion in solution at a concentration of 1 molar and Buffett you have hydrogen gas gaseous hydrogen and a partial pressure of 1 atmosphere since meter since hydrogen is a nonmetal and it doesn't conduct electricity you have to provide a highway through beach electrons can move so we use a platinum electrode so in all exercises you do whenever you see a platinum electrode or graphite electrode is because you used something that in the oxidized or reduced form could not conduct electricity was not a solid that could conduct electricity so therefore platinum for a graphite electrode is used instead which doesn't react in anything it just provides a highway through which electrons can move so this is your standard hydrogen electrode or half cell and then we connect other half cells to this under standard conditions and we put a voltmeter there to measure the voltage the electrical potential difference so for example if I were to put copper to copper half cell here and hook it up to this one with a voltmeter the voltmeter would read positive 0.337 the electrons would be moving from the hydrogen standard electrode toward the copper to standard electrode and it would read plus one point three seven volts now what does that mean plus point three three seven volts which is written on the table over here so one volt is defined as one Joule per Coulomb so both is a measure of electrical potential difference which is similar to gravitational potential difference or height difference and it's units are in terms of joules per Coulomb cool is that you learned that in chem 1a it's the SI unit for charge so you know the for example electrons their charge in terms of coulombs is very very small like 10 to the power minus 19 remember Robert Millikan discovered the charge of electron we call it minus 1 because of the sake of simplicity because proton has the same exact charges electron but opposite but in terms of coulombs this charge is very very small and one mole of electrons six photo to touch them to the 23 electrons carries 9600 96,500 coulombs of charge so one mole of electrons carries 96,500 coulombs of charge and that's called Faraday's cost so that way you can go from moles of electrons to charge and vice-versa so anyways bold is defined as joules per Coulomb so if you have electrical potential difference like if you have a battery that's one and a half bull that means for every Coulomb of charge that goes from the anode to the cathode one and a half joules of energy will be released if the battery was a 9-volt battery that means that for every Coulomb of charge that go from the negative end of the battery to the positive the anode to the cathode nine jewels we'll be loosed so it's a set amount it tells you the potential difference and then how much energy is released depends on how many coulombs of charged make the transition it's kind of like this is our gravitational potential height difference between my two hands now how much energy is released depends on the weight of the thing that drops down so if marker just dropping down less coulombs in this case less mass less Energy's release but for example a large book or something or our notebook drops more energy is released so in here as well the more coulombs make that travel more electrons make that travel more energy through so this simply tells you the potential difference so if you look at zinc it's negative so if I were to hook up zinc half cell to this then the electrons would be going the other way they would go from the zinc half cell - or the hydrogens standard electrode and so as a result this would be minus 0.67 if you use a voltmeter and universe the cathode and anode you'll see will be negative versus positive so in this case they will be negative point six seven which means that the electrons are actually going from the zing toward the hydrogen electrode so that's how you get those values and so they put 1 molar solutions of those guys then they compared them to their standard hydrogen electrode and so that's how they quantify the tendency of those species dirty molecules ions polyatomic ions or elements there are tendencies to want to grab electrons so next we are going to do an example but the video is getting too long so next time we are going to do an example where we put that formula to work and calculate the cell potential let's say I'm gonna use the Daniell cell which I introduced earlier we're gonna measure the cell potential using that table for ourselves so we'll do that next