 In this video we will learn how to write half equations for simple redox reactions. A half equation shows what happens at one of the electrodes during electrolysis. So we do need to be able to complete and balance half equations for these reactions. Remember that oxidation occurs at the anode and reduction occurs at the cathode. Let's have a look at a simple redox reaction. A strip of copper wire is placed in silver nitrate solution. Over time the solution changes color from colorless to bright blue. You will also observe silver metal crystal deposits on what was once copper wire. Why is the solution turned blue? Pause and think. This is a single displacement reaction. Copper metal, which is higher on the reactivity series, has displaced silver in silver nitrate. The solution has turned blue because of the copper two ions in the solution. This is also a redox reaction where a reduction and an oxidation are occurring simultaneously. Hence the term redox. Remember that oxidation means the loss of electron and reduction means the gain of electrons. So for a redox reaction, electron transfer has to happen with one substance losing electron and another substance gaining electron. The silver nitrate is an ionic solution containing AG positive and NO3 negative ions. So here is the equation again with all the ions shown separated. The copper metal has been oxidized because it has lost two electrons to form Cu2 positive ions. If we take out this half reaction, we now have a half equation. Whereas the silver ions have gained electrons to become reduced, represented by this half equation. We are called half equations because each equation represents half a redox reaction. Either the reduction reaction or the oxidation reaction. When the two equations are added together to form the final redox reaction, you can see that everything, including the number of electrons, are balanced. To reform the ionic equation, the electrons are equal on each side and can be removed. What about those nitron ions in the original equation? As the nitron ions appear on both sides of the equation, they are called spectator ions, as they have no effect on the overall reaction. Much like spectators in a football match have no effect on the final result of the game. Here is another redox reaction with iron III chloride oxidizes iodide ions to iodine solid. See if you can write the two half equations. Pause the video and work out the answer. Did you get it right? The iron is reduced and so gains an electron. The iodide ions are oxidized and so lose the electrons to form iodine. So in summary, half reactions represent either an oxidation reaction or a reduction reaction of a redox reaction.