AP Electrochemistry – what do you need to know…

The formula list that is part of your AP packet is here:

Yep, that’s it!

Depending on the equation sheet to help you out in an exam is never the best idea. Do memorize these equations. You do need to know the following:

  1. How to recognize an oxidation or reduction equation and how to write the half reactions.
  2. How to balance a redox reaction.
  3. What a Galvanic vs. Electrolytic cell is and all the parts therein.
  4. Be able to identify a cathode and anode in either of the above cells.
  5. Understand the processes that happen in the cathode, anode, salt bridge, etc.
  6. Calculate the cell potential, E, and understand what it means wrt spontaneity.

After you are comfortable with all the above, we can now relate E to ΔG by the first equation: 

  • Remember that ΔG also relates to the equilibrium constant K.
  • Now we have 3 parallel measures of spontaneity. K, ΔG and E.
  • K>1, ΔG<0 and E>0 for a spontaneous process.

In an electrolytic (non spontaneous) cell, you will be often asked to find the amount of metal deposited when a current (I) is run through the cell for a certain amount of time. You then go through the following process:

I (current)→q (charge)→molese→molesmetal→gramsmetal or the other way, as the question may be.

  1. I → q. This is what the equation on your sheet is for:
  2. q/F = ne, the number of moles of electrons you have used. F here is the faraday’s constant, also in your equation sheet.
  3. Use your reduction equation here, eg. Al3+ + 3 e→ Al. This shows a 3:1 molar ratio between ne and nmetal
  4. Find nmetal using this ratio
  5. Multiply by molar mass to find grams of the metal!