electrochemical

Meaning: An electrochemical cell links a redox reaction to electrical energy. Oxidation at the anode releases electrons, which flow through a wire to the cathode, where reduction occurs. A salt bridge lets ions move to keep each half-cell neutral. A galvanic (voltaic) cell is spontaneous (E°cell > 0, ΔG < 0); an electrolytic cell uses an external voltage to drive a nonspontaneous reaction.

Equation: ΔG° = −nFE°cell, where ΔG° is the standard free energy change (J/mol), n is the moles of electrons transferred per mole of reaction (mol), F is the Faraday constant, 96,485 C/mol, and E°cell = E°cathode − E°anode is the standard cell potential (V).

On the MCAT: Given a table of standard reduction potentials, you identify the cathode, calculate E°cell, and predict electron flow, electrode mass change and salt bridge ion movement. Electrolysis items use Q = It and moles of electrons = Q/F to find the mass of metal deposited.

Common confusion: The anode is not always negative. Oxidation occurs at the anode and reduction at the cathode in both cell types. Only the polarity changes: the anode is negative in a galvanic cell but positive in an electrolytic cell.