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Course: AP®︎/College Chemistry>Unit 9

Lesson 10: Electrolysis and Faraday's law

Quantitative electrolysis

Given the amount of electrical charge that passes through an electrolytic cell, we can calculate the quantity of substances consumed or produced during electrolysis (or vice versa). The total charge is related to the magnitude of the current and the time it runs by the equation I = Q/t, where I is the current in amperes, Q is the charge in coulombs, and t is the time in seconds. Created by Jay.

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• When we calculate amperes over a certain period of time, is that the average amperes? Because we learned that instantaneous E changes as reaction gets closer to equilibrium, and since the concentration of reactants decrease over time, I'd imagine that the reaction gets slower, impacting amperes. If that's the case, then is it average?
• If this were a voltaic cell, then yes the current would decrease as the reaction progressed. However, here we have an electrolytic cell where an external power source is supplying a constant voltage (and therefore a constant current). So the current is constant here because the voltage isn’t originating from the reaction itself, but a battery.

Hope that helps.
• Ok, so I am putting this question here because it is generally about Faraday's constant and all that. Let's say your calculating your change in free energy(delta G). You have the equation delta G=-nFE where n is the moles of electrons, F is the faraday constant, and E is the cell potential(positive for galvanic cells). Does that negative sign apply to the whole equation? And if so, why does the faraday constant never have negative sign if the negative sign is applied to the whole equation? Thanks so much for whoever is gonna help me in advance!