aamc 7R #24 physical sciences

[MikeMitchell]

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Correct answer being A, which I guessed after realizing -.55 was not an answer choice. Why is the Copper not twice +0.34? Obviously missing the fundamentals of this type of question. Thanks in advance.

 

[AlphaMagnum]

Correct answer being A, which I guessed after realizing -.55 was not an answer choice. Why is the Copper not twice +0.34? Obviously missing the fundamentals of this type of question. Thanks in advance.

The standard potentials E (I don't know how to make the degree symbol) for electrochemistry do not get multiplied; it is only the sign which can change.

Basically, if you need to reverse a half-reaction, you can change the sign of the potential for that reaction.

But you don't multiply it or divide it or anything like that, no matter what sort of multiplication/division operation you may have to apply to the half-reaction.

As to why this is the case, I am not sure. It was treated as a 'given' in my IB Chemistry course and I don't have my MCAT prep book handy to look for any more detail. I doubt that you'll be asked that, though.

 

[muhali3]

Think about batteries. You can have a really big battery and a really small battery that are both 1.5 Volts. The bigger battery has a longer life but the cell potential (voltage) is the same. The moles don't affect the voltage, just the longevity.

When you think of a galvanic cell, you think of electrons falling from high potential energy to low potential energy.

The voltage is the potential energy drop per unit charge. It is not affected by how much charge you have.

For example, if I drop ten balls from the top of a building vs. one ball from the top of a building, the change in potential energy per ball is the same in either case.

 

[MikeMitchell]

Thanks, excellent explanation.