Electrochemistry gets easier once one fact is locked in: the anode is always oxidation and the cathode is always reduction, no matter which type of cell is being discussed. Everything else builds from there.
Galvanic (voltaic) cells
A galvanic cell uses a spontaneous redox reaction to generate electrical energy, the basic idea behind every battery. Electrons flow from the anode to the cathode through an external wire, and the cell has a positive standard cell potential, corresponding to a negative, thermodynamically favorable Gibbs free energy.
Electrolytic cells
An electrolytic cell runs the process in reverse: it uses an outside source of electrical energy to force a nonspontaneous redox reaction to happen, which is how electrolysis works. The reaction being driven would have a negative cell potential on its own, and the external power source is what makes it happen anyway.
Anode and cathode never change meaning
A simple memory device: "AN OX, RED CAT." Anode is where oxidation happens, cathode is where reduction happens, and that's true for both galvanic and electrolytic cells. What does flip between the two cell types is which electrode is positive and which is negative, since an electrolytic cell's external power source reverses the usual polarity.
Calculating standard cell potential
Formula
Worked example
Where students actually lose points here
Assuming the anode is always negative
That's only true for a galvanic cell. In an electrolytic cell, the external power source reverses the usual polarity, making the anode positive instead.
Subtracting E° values in the wrong order
E°cell is cathode minus anode, always using both values as standard reduction potentials. Reversing the subtraction flips the sign of the answer.
Mixing up which half reaction is the cathode
The half reaction with the higher, more positive standard reduction potential is the cathode, since it's more favorable to be reduced there. Picking the wrong one flips which electrode is which throughout the whole problem.
One consistent rule across two cell types
Electrochemistry looks like two separate topics at first, but anode-oxidation and cathode-reduction never change, which makes the two cell types much less confusing once that's clear.
Common questions
What's the difference between a galvanic cell and an electrolytic cell?
A galvanic cell uses a spontaneous redox reaction to generate electrical energy, like a battery. An electrolytic cell does the opposite, using outside electrical energy to force a nonspontaneous redox reaction to occur.
Is the anode always negative?
Only in a galvanic cell. In an electrolytic cell, the external power source reverses the usual polarity, so the anode becomes positive instead.
How do you calculate standard cell potential?
E°cell equals the cathode's standard reduction potential minus the anode's standard reduction potential. The half reaction with the higher reduction potential is the cathode.