Correcting Frost Diagram Misconceptions Using Interactive Frost Diagrams

Abstract

Frost diagrams provide convenient illustrations of the aqueous reduction potentials and thermodynamic tendencies of different oxidation states of an element. Undergraduate textbooks often describe the lowest point on a Frost diagram as the most stable oxidation state of the element, but this interpretation is misleading because the thermodynamic stability of each oxidation state depends on the specific redox conditions in solution (i.e., the potential applied by the environment or an electrode). Further confusion is caused by the widespread use of different, contradictory conventions for labeling the y-axis of these diagrams as either nE°or −nE°, among other possibilities. To aid in clarifying these common points of confusion, we introduce a series of interactive Frost diagrams that illustrate the conditional dependence of the relative stabilities of each oxidation state of an element. We include instructor's notes for using these interactive diagrams and a written activity for students to complete using these diagrams.

Elemental Aspects of Transition Metals Pertinent to Organometallic Chemistry: Properties, Periodicity, Curiosities, and Related Main Group Issues

“…The Frost diagrams , shown in Figure are a means of assessing relative free energies of compounds with respect to assigned formal oxidation states (FOSs). The data are chosen relative to a specific reference potential, which is usually the standard hydrogen electrode (SHE) common in most data compilations.…”

Electrocatalysts for Inorganic and Organic Waste Nitrogen Conversion

“…Nitrogen can be found with oxidation states that range from −III to +V. As shown in the Frost diagram (Figure ), the thermodynamic stability of a N compound with different oxidation states depends on the average Gibbs molar energy and the specific conditions of the solution . A compound located at an energy lower than that of the connecting line between neighboring species is more stable than neighboring N compounds under a certain pH.…”

“…As shown in the Frost diagram ( Figure 2 ), the thermodynamic stability of a N compound with different oxidation states depends on the average Gibbs molar energy and the specific conditions of the solution. 65 A compound located at an energy lower than that of the connecting line between neighboring species is more stable than neighboring N compounds under a certain pH. Thus, the neighboring compounds will tend to be comproportionate to the most stable lower-energy compound.…”

Direct Electrooxidation of Ammonia-Enriched Wastewater Using a Bipolar Membrane-Integrated Electrolytic Cell

“…− ions due to it having the highest oxidation state [20]. In addition, the selective conversion of ammonia into nitrogen gas or nitrite/nitrate is another concern for complete nitrogen removal in wastewater treatment.…”