Let's compare that voltaic cell to an electrolytic cell, so on the right. An electrolytic cell uses an electric current to drive a nonspontaneous redox reaction. So if we look at the overall reaction here, we're starting with solid copper and zinc two plus ions in solution. And we're going to copper two plus ions in solution and solid zinc. So this is the reverse of the reaction we just talked about.
The reactants for this reaction were the products for this reaction. To find the standard cell potential, all we have to do is take the negative of this cell potential, because we just reversed the reaction. So if we reverse the reaction, we just change the sign. So the cell potential, the standard cell potential, would be negative 1. A negative value for your cell potential means a non-spontaneous redox reaction. So this doesn't occur on its own. Solid copper doesn't just turn into copper two plus and zinc two plus doesn't turn into solid zinc.
It needs some help in order to do that. It needs an external voltage source, like a battery, to drive this reaction and force it to happen. So we need a battery here. Let's put in a battery in our little circuit.
So we have a battery. We need the negative terminal to be on the left side and the positive terminal to be on the right side. So this is our voltage source. And we need at least 1.
And in practice, it turns out to be more than 1. So our negative terminal of the battery is where we get electrons. So electrons come out of the negative terminal of the battery and deliver electrons to the zinc electrode.
So electrons are forced onto the zinc electrodes. Let me draw on here two electrons. And now we have two zinc plus ions in solution. The zinc anode gradually diminishes as the cell operates due to the loss of zinc metal. The zinc ion concentration in the half-cell increases.
Because of the production of electrons at the anode, it is labeled as the negative electrode. The electrons that are generated at the zinc anode travel through the external wire and register a reading on the voltmeter. They continue to the copper electrode. Electrons enter the copper electrode where they combine with the copper II ions in the solution, reducing them to copper metal.
The electrode at which reduction occurs is called the cathode. The cathode gradually increases in mass because of the production of copper metal. The concentration of copper II ions in the half-cell solution decreases. The cathode is the positive electrode. Chemistry Electrochemistry Galvanic Cells.
Mar 31, Explanation: Before we go into the internal workings of the two types of cell it helps if we adopt a "black box" approach to these devices. Conventional electric current is said to flow from the positive terminal to the negative one. This, however, is the convention we are left with. Now lets see how this applies to an electrolytic cell and a galvanic cell. In an electrolytic cell electrical energy is used to cause chemical change. These electrons flow round the external circuit and arrive at the copper electrode.
A good way of remembering cathode and anode in a cell is to realise that: "Oxidation occurs at the anode" and "Reduction occurs at the cathode" Care must be taken when physically labelling the electrodes on any electrical device. Negatively charged ions lose electrons at the anode. These are half equations for some reactions at the anode:. Write a balanced half equation for the formation of bromine, Br 2 , from bromide ions, Br -.
0コメント