Electrochemistry: Redox, Cells, and Potential

Vocabulary flashcards covering the core concepts of electrochemistry including redox definitions, reduction potentials, cell types (galvanic vs electrolytic), and thermodynamic relationships.

Redox

The pairing of oxidation and reduction where electrons leaving one molecule must land on another; electrons are never created or destroyed.

Oxidation

A process defined by the loss of electrons, loss of bonds to $H$, gain of bonds to $O$ (electronegative atoms), or an increase in oxidation number.

Reduction

A process defined by the gain of electrons, gain of bonds to $H$, loss of bonds to $O$ (electronegative atoms), or a decrease in oxidation number.

Reduction Potential ($E^\circ$)

A ranking of how badly a species wants to gain electrons, written as the tendency for the reaction: oxidized form + $e^- \rightarrow$ reduced form.

Standard Hydrogen Reference

The zero point for reduction potentials, defined by the reaction $2H^+ + 2e^- \rightarrow H_2$ where $E^\circ = 0$.

Oxidation Potential ($E^\circ_{ox}$)

The reduction potential of a reaction with the arrow flipped and the sign reversed ($E^\circ_{ox} = -E^\circ_{red}$).

Spontaneity and $E_{cell}$

A relationship where the cell is spontaneous if $E_{cell} > 0$ ($\Delta G < 0$) and nonspontaneous if $E_{cell} < 0$ ($\Delta G > 0$).

Faraday Constant ($F$)

A constant used in free energy calculations for electrochemical cells, equal to $96,485\,C/mol$.

Gibbs Free Energy Equation ($\Delta G^\circ$)

$\Delta G^\circ = -nFE^\circ_{cell}$, where $n$ is the moles of $e^-$ transferred and $F$ is the Faraday constant.

Galvanic (Voltaic) Cell

A spontaneous electrochemical cell where $E_{cell} > 0$ and the electrode with the higher reduction potential serves as the cathode ($+$, reduction) and the lower potential electrode serves as the anode ($Negative$, oxidation).

Electrolytic Cell

A nonspontaneous (forced) electrochemical cell where $E_{cell} < 0$ and the cathode is at a lower reduction potential than the anode.

AN OX / RED CAT

A rule that holds true in all cells: ANode = OXidation and REDuction = CAThode.

Ions Go Home

The movement of ions in an electrolyte where cations migrate toward the cathode and anions migrate toward the anode.

Higher $E^\circ$ Rule

Across any electrochemical cell, the electrode with the higher reduction potential is the positive terminal.

Electrode Charges (Galvanic vs. Electrolytic)

In galvanic cells, the anode is negative ($-$) and the cathode is positive ($+$). In electrolytic cells, the anode is positive ($+$) and the cathode is negative ($-$).