Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Uber-Dan on April 08, 2022, 01:18:55 AM
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Hello all,
So I've been learning about standard electrode potentials in class. I know that they are measured under standard conditions, but I haven't been able to find any information on what internal resistance is considered "standard". There will obviously always be some, but do they just assume it is zero because the circuits they can design may as well have zero resistance?
Thanks in Advance
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Resistance is left undefined ("whatever the solution has"). It doesn't matter for potential measurements done without load.
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So would any changes in resistance in a galvanic cell (for instance the resistance in the salt bridge) not affect the voltage, but the current instead?
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This is a bit more complicated. Do you know what an ohmic drop is?
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No, but after a quick google search, it seems that it is the difference between the applied voltage and the actual voltage?
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Something like that, although "applied" and "actual" are just one of ways describing it. Broadly speaking when you have current i flowing through a resistance R, and you measure voltage on the contacts, it will be -iR. Ideal battery has no internal resistance, so it always produces the same voltage, but no practical battery is ideal, so they all behave as if their voltage was lower under load.
Knowing the internal battery resistance is necessary to estimate the measurement error of the voltage, but as typical digital voltmeter has internal resistance in the 10 MΩ range, and typical battery (like AA) has an internal resistance in the single Ω range, it rarely really matters.