Electrode Potentials and Electrochemical Cells

This set of vocabulary flashcards covers the fundamentals of electrode potentials, electrochemical cell notation, standard conditions, and the various types of rechargeable and non-rechargeable batteries.

Electrode (Half Cell)

An arrangement where a rod of metal is dipped into a solution of its own ions, setting up an equilibrium such as $Zn(s) \rightleftharpoons Zn^{2+}(aq) + 2e^{-}$. Pairs of these can be joined to make an electrical cell.

Salt Bridge

A component used to complete an electrical circuit between two half cells (commonly a piece of filter paper soaked in saturated potassium nitrate) to avoid further metal/ion potentials.

Standard Hydrogen Electrode

The reference half cell with a potential defined as zero, consisting of hydrogen gas bubbled into a $1.00\,mol\,dm^{-3}$ solution of $H^{+}(aq)$ ions over a platinum electrode at $100\,kPa$ and $298\,K$.

Standard Electrode Potential ($E^{\theta}$)

The electromotive force (emf) measured when a half cell is connected to a standard hydrogen electrode under standard conditions of $1.00\,mol\,dm^{-3}$ for ions, $298\,K$, and $100\,kPa$ for gases.

Reducing Agent

A species that releases electrons; systems with more negative $E^{\theta}$ values are better at this process than hydrogen.

Electrochemical Series

A list of electrode potentials (reduction potentials) arranged in order, typically with the most negative values at the top.

Daniell Cell

An electrochemical cell using zinc and copper electrodes that generates an emf of $1.1\,V$ via the overall reaction $Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)$.

Phase Boundary

Represented by a single vertical solid line ($|$) in a cell diagram, it indicates the interface between different states of matter, such as a solid metal and an aqueous solution.

Double Vertical Line ($||$)

The conventional IUPAC representation of a salt bridge in a cell diagram.

Standard Emf Formula

The calculation used to determine the voltage of a cell based on its right-hand and left-hand electrodes: $emf = E^{\theta}(R) - E^{\theta}(L)$.

Leclanché Cell

A non-rechargeable zinc/carbon cell containing an ammonium chloride paste electrolyte with a zinc canister and a central carbon rod surrounded by manganese(IV) oxide and powdered carbon.

Lead-Acid Battery

A rechargeable battery used in cars consisting of six $2\,V$ cells in series; it uses lead plates and lead(IV) oxide plates dipped in a sulfuric acid electrolyte.

Lithium Ion Cell

A lightweight rechargeable battery used in mobile gadgets that employs a lithium cobalt oxide ($LiCoO_2$) positive electrode, a carbon negative electrode, and a solid polymer electrolyte.

Hydrogen-Oxygen Fuel Cell

A cell that generates an emf of $1.23\,V$ by reacting hydrogen and oxygen over a platinum-based electrode to produce water as the only by-product.

Platinum Black

A coating of finely divided platinum used on electrodes to increase surface area and allow reactions to proceed rapidly, particularly in the hydrogen electrode.

Metal Hydrides

Solid compounds used to store hydrogen safely under pressure; the gas is later released by gentle heating.