Electrode Potentials and Electrochemical Cells Flashcards

This set covers vocabulary related to electrode potentials, the design and measurement of electrochemical cells, standard reference electrodes, and various commercial battery types as described in the lecture notes.

Electrochemical cell

A system where two different metals are placed in a salt solution and connected together so that an electric current flows from the more reactive metal to the less reactive metal.

Electrode (or half cell)

An arrangement where a rod of metal is dipped into a solution of its own ions, establishing an equilibrium such as $Zn(s) \rightleftharpoons Zn^{2+}(aq) + 2e^-$.

Salt bridge

A piece of filter paper soaked in a salt solution (usually saturated potassium nitrate) used to complete the electrical circuit and avoid further metal/ion potentials.

Potential difference (Voltage)

An electrical 'push' or pressure that tends to make current flow, often measured at a value of $1.10V$ for a standard zinc and copper cell.

Standard hydrogen electrode

The standard reference half cell where hydrogen gas at $100 \text{ kPa}$ is bubbled into a $1.00 \text{ mol dm}^{-3}$ solution of $H^+(aq)$ ions at $298 \text{ K}$, defined as having a potential of zero.

Finely divided platinum black

A coating on the platinum metal in a hydrogen electrode used to increase surface area and allow the reaction to proceed rapidly.

Electromotive force (emf)

Represented by the symbol $E$, it is the potential difference of a cell measured when it is connected to a standard hydrogen electrode.

$$E^\theta$$

The symbol for standard electrode potential, measured under conditions of $1.00 \text{ mol dm}^{-3}$ ion concentration, $100 \text{ kPa}$ pressure, and $298 \text{ K}$ temperature.

Electrochemical series

A list of electrode potentials (reduction potentials) arranged with the most negative values at the top, showing the relative strength of reducing agents.

Reducing agent

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

Phase boundary

Indicated by a vertical solid line in conventional cell representation, showing the contact between different states of matter (e.g., solid and solution).

IUPAC convention for cells

A shorthand for writing cell diagrams where the species with the highest oxidation state is written next to the salt bridge (represented by a double vertical line).

emf calculation formula

$emf = E^\theta(R) - E^\theta(L)$, where $R$ represents the right-hand electrode and $L$ represents the left-hand electrode.

Daniell cell

An early electrical cell containing zinc and copper electrodes that provided an emf of $1.1V$, originally used for telegraphic communications.

Leclanché cell

The basis of most ordinary disposable batteries, consisting of a zinc canister (negative electrode) and a carbon rod (positive electrode) in an ammonium chloride paste electrolyte.

Lead-acid battery

A rechargeable battery consisting of six $2V$ cells connected in series, using lead and lead(IV) oxide plates in a sulfuric acid electrolyte.

Lithium ion cell

A lightweight rechargeable cell used in mobile devices where the positive electrode is lithium cobalt oxide ($LiCoO_2$), the negative electrode is carbon, and the electrolyte is a solid polymer.

Hydrogen-oxygen fuel cell

A cell that reacts oxygen and hydrogen using porous platinum-based electrodes and an alkaline electrolyte (sodium hydroxide) to generate electricity and water.

Fuel cell overall reaction

The chemical process $2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$ which generates an emf of $1.23V$.

Metal hydrides

Solid compounds used to store hydrogen safely by absorbing the gas under pressure and releasing it through gentle heating.