Different types of electrochemical cells that exist can be connected to the idea of spontaneity. Whether an electrochemical cell is spontaneous or not, helps us to categorize them and split them into 2 different camps. Here we're going to say in terms of spontaneity, the following correlations between the following variables can be made. So here we have Gibbs free energy under standard conditions. That's what this little circle here means. Standard conditions being 25 degrees Celsius, where your pH is equal to 7, and your concentration is equal to 1 molarity. We also have k, which is our equilibrium constant. We have our cell potential. We have ΔS, which is our entropy. And then we have Q versus K. Q is our reaction quotient. It's used as a way to determine if we are at equilibrium or not. From these variables, we can determine the type of reaction classification we have, meaning is it spontaneous, non spontaneous, or at equilibrium and from that, we can determine what type of electrochemical cell we have. So if we take a look at the first row, when ΔG < 0, that means that k > 1, your cell potential will be greater than 0, ΔS in here, this is ΔS total or ΔS universe based on the second law of thermodynamics. Our Q will be less than K. Now, in this part, this helps us determine the direction. If you set up a number line and k is here in the middle and Q is less than it, then Q is always going to shift in the direction to get to K, our equilibrium constant. So our reaction would shift in the forward direction. All of these variables are telling me one thing, that my reaction is spontaneous. And when we have a spontaneous reaction, that means our electrochemical cell is a galvanic or voltaic cell. Next, if we reverse the order of all the signs where ΔG > 0, k < 1, your cell potential is less than 0, as well as your entropy of your universe is less than 0. Here, Q would be greater than K. Here we'd move in the reverse direction in terms of our chemical reaction. Here this would mean that our reaction is non spontaneous. When you have a non spontaneous reaction, that means your electrochemical cell is an electrolytic cell. We'll talk a bit more about electrolytic cells down below, but just realize here electrolytic cells represent non spontaneous electrochemical cells. Then finally when everything is equal to their given value, this means that we are at equilibrium. When an electrical cell is at equilibrium, that means it represents a dead battery. It has discharged all its electricity or it's consumed all the electricity, therefore, it is at a state of equilibrium. Now, we said that an electrochemical cell represents a non spontaneous electrochemical cell. Here because it's non spontaneous, it requires an outside energy source to work. So here it requires a battery and so because it requires a battery, it consumes electricity. Remember, a galvanic/voltaic cell produces or discharges electricity, and an electrolytic one consumes electricity. Here we have an example of a basic electrolytic cell. Here we have the implementation of a battery in order to drive electrons from one side to the other side. Now, here our positive electrode will actually be the anode. Remember for a galvanic or voltaic cell, the anode was negative. Now because we're dealing with an electrolytic cell, it's positive and now the cathode is negative. If we think about it, it doesn't make too much sense for negative electrons to want to travel to a negative electrode. Like charges repel each other. That's why we require a battery. The battery is there to force the reaction to occur because it's not a natural process. Here, the electron affinity, if we're talking in terms of this, the image here, we'd say that the electron affinity for the cathode would be low. Electrons do not want to go to the negative cathode and then the ionization energy for the anode would be high. It would take a lot of energy to remove the negative electrons from the anode. They just don't want to leave the anode to go to an electrode. So basically, things are reversed in terms of a galvanic cell versus an electrolytic cell. The only common thing, the thing that's always consistent, is that the anode still undergoes oxidation and the cathode still undergoes reduction. The problem here though is it's not a natural process because negative electrons again don't want to go to something with the same charge that it has. That's why batteries are required to force this reaction to happen. So this is the common feature of both types of electrochemical cells, whether they're spontaneous or non spontaneous. Anode always undergoes oxidation whereas the cathode always undergoes reduction. So just remember the differences an electrolytic cell versus a galvanic/voltaic cell. And remember the different variables when you look at them in conjunction with one another help to determine if a chemical reaction is spontaneous, non spontaneous, or at equilibrium.
Table of contents
- 1. Chemical Measurements1h 50m
- 2. Tools of the Trade1h 17m
- 3. Experimental Error1h 52m
- 4 & 5. Statistics, Quality Assurance and Calibration Methods1h 57m
- 6. Chemical Equilibrium3h 41m
- 7. Activity and the Systematic Treatment of Equilibrium1h 0m
- 8. Monoprotic Acid-Base Equilibria1h 53m
- 9. Polyprotic Acid-Base Equilibria2h 17m
- 10. Acid-Base Titrations2h 37m
- 11. EDTA Titrations1h 34m
- 12. Advanced Topics in Equilibrium1h 16m
- 13. Fundamentals of Electrochemistry2h 19m
- 14. Electrodes and Potentiometry41m
- 15. Redox Titrations1h 14m
- 16. Electroanalytical Techniques57m
- 17. Fundamentals of Spectrophotometry50m
16. Electroanalytical Techniques
Coulometry
16. Electroanalytical Techniques
Coulometry - Online Tutor, Practice Problems & Exam Prep
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Electrochemical cells can be classified based on spontaneity, determined by Gibbs free energy (ΔG), equilibrium constant (K), cell potential (Ecell), and entropy (ΔS). A spontaneous reaction (ΔG < 0) indicates a galvanic cell, while a non-spontaneous reaction (ΔG > 0) indicates an electrolytic cell, which requires an external energy source. At equilibrium (ΔG = 0), the cell behaves like a dead battery. In both cell types, the anode undergoes oxidation and the cathode reduction, but their charge roles differ in electrolytic cells, necessitating a battery to drive the reaction.
Coulometry
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Coulometry
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Video transcript
Through the use of electrical current we are dealing with electrolytic cells that are non-spontaneous in nature.