표준 전극 전위

Ranking the electron-grabbers

• The electrode potential 电极电势 $E$ shows how easily a half-cell 半电池 is reduced.
• We measure it against a fixed reference under standard conditions.
• Combining two half-cells gives a cell potential 电池电势.

The reference and measuring E°

• The standard hydrogen electrode 标准氢电极 is the zero reference: $\text{H}_2$ at 1 atm over platinum in $1\ \dfrac{\text{mol}}{\text{dm}^3}$ $\text{H}^+$, defined as 0.00 V.
• To measure a half-cell's $E^{\ominus}$, connect it to the hydrogen electrode and read the voltage (always written as a reduction).

The electrochemical series of standard electrode potentials

Combining half-cells

• Polarity: the more negative electrode is the negative terminal; electrons flow from it through the circuit.
• Reactivity: a more positive $E^{\ominus}$ → better oxidising agent 氧化剂; a more negative $E^{\ominus}$ → better reducing agent 还原剂.

Electrolysis electroplates an object with a thin, shiny layer of metal such as chromium.

Reading the electrode-potential table

• The more positive E°, the more easily the species is reduced (a stronger oxidising agent).
• The more negative, the stronger the reducing agent.

The standard hydrogen electrode reference

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