Electrochemistry and Redox Reactions (Chapter 20)

Practice flashcards covering redox balancing, oxidation numbers, electrochemical cell components, cell potential calculations, and electrolysis.

Oxidation Number

The formal charge assigned to an atom in a substance indicating the number of electrons lost or gained; for example, chromium is $+6$ in $(NH_4)_2Cr_2O_7$, carbon is $+4$ in $K_2CO_3$, and iron changes from $+3$ in $Fe_2O_3$ to $0$ in $Fe$.

Hydride Ion Oxidation State

The oxidation number of hydrogen when combined with active metals in binary hydrides such as $CaH_2$, where calcium has an oxidation state of $+2$ and hydrogen has an oxidation state of $-1$.

Oxidizing Agent

A species that gains electrons and is reduced during a chemical reaction, causing another species to be oxidized; characterized by a decrease in oxidation number, typically nonmetals located on the upper right of the periodic table such as $F_2$ or metals in high oxidation states such as $Mn^{7+}$.

Reducing Agent

A species that loses electrons and is oxidized during a chemical reaction, causing another species to be reduced; characterized by an increase in oxidation number, typically active metals located on the left side of the periodic table such as $Li$ or $K$.

Anode

The electrode in an electrochemical cell at which oxidation occurs; in a voltaic cell, it serves as the negative terminal ($-$) from which electrons flow outward into the external circuit.

Cathode

The electrode in an electrochemical cell at which reduction occurs; in a voltaic cell, it serves as the positive terminal ($+$) where electrons arriving from the external circuit are accepted.

Salt Bridge

An inverted U-tube or porous barrier filled with an electrolyte solution connecting two half-cells that completes the electrical circuit and maintains electrical neutrality by allowing anions to migrate toward the anode and cations toward the cathode.

Voltaic Cell Components (Diagram)

The labeled components of a standard two-compartment voltaic cell: (a) negative electrode half-cell solution, (b) anode, (c) external electron flow from anode to cathode, (d) voltmeter, (e) cathode, (f) positive electrode half-cell solution, (g) salt bridge, (h) flow of cations toward cathode, and (i) flow of anions toward anode.

Standard Reduction Potential ($E^\circ_{red}$)

The potential of a reduction half-reaction measured in volts ($\text{V}$) at standard state conditions ($25\,^\circ\text{C}$, $1.0\text{ M}$, $1\text{ atm}$) relative to the standard hydrogen electrode ($0\text{ V}$); higher positive values indicate stronger oxidizing abilities.

Electrochemical Cell Shorthand Notation

The standardized symbolic format for describing an electrochemical cell from anode to cathode: Anode(s) | Anode ion(aq) || Cathode ion(aq) | Cathode(s), exemplified by $Zn(s) \mid Zn^{2+}(aq, 1.0\text{ M}) \parallel Ag^+(aq, 1.0\text{ M}) \mid Ag(s)$.

Standard Cell Free Energy ($\Delta G^\circ$)

The standard free energy change of an electrochemical cell related to the standard cell potential by $\Delta G^\circ = -nFE^\circ_{cell}$, where a positive $E^\circ_{cell}$ corresponds to a negative, product-favored free energy value.

Cell Equilibrium State

The condition reached when an operating voltaic cell runs to completion and dynamic equilibrium is attained, at which point the cell potential becomes zero ($E_{cell} = 0$).

Electrolysis

The process of using electrical energy (external electrical current) to drive a nonspontaneous chemical reaction.

Halogen Oxidizing Strength Trend

The periodic ranking of halogen oxidizing ability in order of decreasing strength down the group: $F_2 > Cl_2 > Br_2 > I_2$.

Metal Reducing Strength Trend

The periodic activity ranking of metals as electron donors in order of decreasing reducing strength: $K > Mg > Fe > Au$.

Faraday's Constant in Electrolysis

The constant representing the electric charge carried by one mole of electrons ($96{,}485\text{ C/mol }e^-$ or approximately $96{,}500\text{ C/mol }e^-$), utilized to calculate the mass of metal plated out over a specific time and electric current.