Learn about Senior Chemistry, Redox 2, in this comprehensive video by bannanaiscool.
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Male Speaker: So when approaching a question like this one the first thing you want to do is take any kind of ionic compound, any compound and break it up into ions and solution and then check this redox chart that you have reduction potentials chart to find the high substances on the left side, and reactivity to lower substance on the right, if there are all written as reduction reactions and that the highest voltages that see on the far right hand side, are listed, from highest positive value to lowest negative value, okay. Now when you do that you have to get for this one, a list of chemicals first I like to start with the list, that says I got lead solid and silver and nitrate irons, that's silver nitrates we are going to around the solution and waters, waters are reducing antioxidizing agents on the chart, on both sides, but the highest one of the left is the silver iron and the lowest on the right is the lead iron, so what's appeared lets down here and we've got is a redox reaction that can occur, now all we do is this find the SOA which is the one of the left hand side, and all you do is you write right half reaction here from left to right exactly the way it says on the chart. Just write to that, but the one that's the SRA on the right side SRA and reducing agent it stress with the right you got to take that reaction and realize, that If you copied it from left to right as well, you will have to reduction reactions. So you reverse it the SRA, On the right side gets reversed and you take that reaction, the half reaction that you see in the book and reverse it so you make it oxidation, and then you can add it to the reduction reaction. When you do that, you have to make sure that the electrons cancel, and in order to make sure that you have got to see that there is a ratio here, 2 electrons being lost but I only gain one so we've got to run through this reaction, twice this half reaction gets multiplied by 2 then add into this once so the electrons can cancel can have electrons left over in an adequate, it have to cancel so you get 280 positive plus lead and that's going to make lead ions and silver that's a solid that's AQ that AQ, that's not AQ that's a salt, sorry okay now here is the thing, that's the net reaction and you can find what they call the voltage would that be actually or the e not the E just stands for the voltage and not means standard conditions of 25 degree celsius and one atmosphere of pressure. The E value in the book for this reaction is 0.80volts, the E value for this reaction is negative 1.23 but if you reverse the equation you reverse this sign and so it becomes positive 0.13 volts, all you do to get the E not of the net equation is to add those two voltages together add the SOA is voltage to the reverse of the SRA and you get 0.93 volts by the way you know that means that means this reaction does take replace because it produces electricity, the reverse of this reaction repeat a negative 0.93, and it wouldn't actually will occur naturally. When a reaction occurs it has got a positive voltage, we says its spontaneous, and that will mean on this chart that will be left over right oxidizing agent over reducing agent, but if its right over left interms of the strongest oxidizing and reducing agent, you get a reaction that doesn't occur naturally and normally and that's going to happen negative voltage and its called non spontaneous.