Standard Reduction Potential
Definition
A ranking of how badly a species wants electrons, measured in volts against hydrogen's zero: the cheat sheet for predicting redox reactions.
Symbol: · Unit: V
Technical definition
Standard reduction potential is the voltage of a half-reaction under standard conditions (1 M, 1 atm, 25 C) versus the standard hydrogen electrode at 0.00 V. More positive means a stronger oxidizing agent, and the cell potential is cathode minus anode.
Example
F2 has E = +2.87 V (fierce oxidizer) while Li+ has E = -3.04 V (lithium metal is a fierce reducer): the table spans nearly 6 volts.
Common confusion
E is intensive: it does not change if you double the reaction coefficients. Gibbs energy scales with moles, but the potential stays the same.