right electrochemical cells they can be a little bit confusing let's try and demystify them the basic setup of an electrochemical cell is you have two different metals that are dipped in a salt solution of their own ions and this produces an emf or an electromotive force that's just a posh name for a potential difference or a voltage that actually causes current to flow so that means electrons flow through the wire that is connecting the two metals or the two electrodes and we need to complete the circuit somehow so we have this salt bridge in between usually it's a bit of filter paper that's been dunked in potassium nitrate and that completes the circuit by allowing ions to move between the two what we call half cells why does this work then well it's because we have two different metals and the more reactive metal loses its electrons more easily than the other and so that's the one that's oxidized in this case with zinc and copper it's the zinc that's more reactive it's going to be oxidized and the other metal is reduced just so you know we can actually do this with the same metal as the electrode as long as this inert in different solutions of ions so for example fe2 plus and fe 3 plus in our solutions the metal we use for the electrode though has to be inert means it doesn't react with the ions so something like platinum does the job we'll see that being used in a minute now the thing is that both oxidation and reduction can occur at each electrode and so that means they're reversible that's kind of evident from the fact that if we use the more reactive metal than zinc instead of copper then the zinc would get reduced instead so what we do is write the half equations like this and when we write reversible half equations we always have the reduction reaction going forward that means the electrons are on the left so which way does it go for each well of course it's the more reactive metal that's oxidized like we said so that means that we will have the forward reaction for the copper because it is reduced but then for the zinc it's the reverse reaction that happens yes we can think about it in terms of reactivity of metals but also we can compare their electrode potentials what we can do is refer to a table or list of different metals in salt solutions with their ions here's a list of metals it's not every metal of course but here we can see that zinc has a lower electrode potential it's more negative so it's oxidized so that means the copper is going to be reduced cu 2 plus plus 2 electrons makes that solid copper so writing the whole equation for the reaction of what's going on in our electrochemical cell we combine the two half equations and so we have both of the reduction and the oxidation reactions happening going forward because we have both happening this is of course a redox reaction where do we get these numbers from though well these are all relative to hydrogen if you have hydrogen pumped in to a solution and our electrode is a platinum electrode so it's inert like we saw earlier and we have in the other half cell the metal that we're looking at with a solution of its ions then we can see whether it has a positive electrode potential or negative electro potential compared to this standard hydrogen one so that means hydrogen is going to be that zero and then everything else is plus so many volts or minus so many volts relative to that and because the conditions can change how our reaction occurs then we need to make sure that our solutions are one mole per decimeter cubed and it happens at rtp as well so 298 kelvin and 100 kilopascals one atmosphere to find out the actual emf produced by an electrochemical cell we just find the difference in electrode potentials between our two metals and so therefore just one and take away the other of course one of them might be negative so just be careful with that so it's useful to have a shorthand way of writing or drawing what an electrochemical cell is made up of so this is how we do it we have on the left the reduced form then oxidized form on the left and then we have a double line in between representing the salt bridge and then the oxidized form of reduced form for the other metal on the right so for example for our setup that we had to begin with it would be the solid zinc electrode and the zinc eyes in solution other side of salt bridge copper ions and then the solid copper electrode batteries are a type of electrochemical cell you probably know one example is lithium ion batteries they're very common say in your phone so they have in them a graphite electrode and another electrode for example lithium cobalt oxide and the electrolyte that links them is a lithium salt we know it has to have lithium ions in it don't we so the reactions going on of the electrodes well we have the lithium is oxidized to turn it into lithium ions they go to the other electrodes where they join together and they're reduced to turn into this complex ion a little bit of a spin on our standard electrochemical cells hydrogen fuel cells are all the rage everybody seems to be talking about them at the minute i'm not sure how viable they are but i'm willing to be proven wrong but here's the basic setup how they work we have two sides to it we have one side where hydrogen is pumped in and the other side where oxygen is pumped in and so those molecules then approach these platinum electrodes and in between we have a solution of potassium hydroxide now the important thing is that we have a membrane that is separating the solution and the electrodes why well that's because we don't want the oxygen and the hydrogen molecules to go into the solution we only want o h ions so that's what happens it's an anion exchange membrane so what happens we end up with hydroxide ions being produced they travel through the membrane and then over to where the h2 is and they join together with the hydrogen to make just pure water h2o and then that is exhausted from the system so this whole process of the oh ions going through the electrodes that results in electrons being transferred through the wire that's connecting the two platinum electrodes and so we have our emf and our current and so we can have whatever we want say a car or a light whatever in that circuit and of course the big advantage of hydrogen fuel cells is that they don't release any pollution yes carbon dioxide is peddled as a big bad gas regardless of whether that's true or not i think we can all agree that sulfur dioxides and nitrous oxides they're definitely bad this doesn't release any of those which is really good so i hope you found this helpful if you did please leave a like if you have any suggestions on what i could do next pop in a comment down below or head over to the discord and put it there see you next time