About driving forces in nature : concepts, interpretations and misunderstandings

Prepared for presentation within the Didactic Section of Polish Chemical Society, the study summarizes selected problems and concepts of teaching the basics of chemical reaction energetics as part of chemical undergraduate studies. The following problems are discussed: 1) indication of misunderstandings related to the definition of standard states in thermodynamics, with particular emphasis on the unfortunate assignment of the temperature of 298.15 K as "standard temperature", 2) problems with the interpretation of entropy as a "measure of disorder", with a recommendation regarding for understanding entropy as a measure of the number of ways to distribute the total energy of the system between the available degrees of freedom of motions, in terms of the quantum representation, i.e. the energy characteristics of a substance through sequences of energy levels, 3) a proposal to introduce the issue of thermodynamic driving forces of a chemical reaction based on the characteristics of the water evaporation process under different conditions, which favors the distinction of any reaction driving force from its standard driving force, as well as the distinction of such forces for isochoric and isobaric systems, both one- and multi-component, (4) the necessity to take into account the entropy of mixing of reagents to deepen the understanding of changes in the driving force of the reaction on the way to the state of chemical equilibrium, and 5) various interpretations of the influence of temperature on the equilibrium composition of the reacting system (Le Chatelier-Braun rule), with a recommendation for molecular interpretation, showing the role of differences in energies and sequences of energy levels of reactants and products for the value and direction of changes of the equilibrium constants of the reaction with temperature, taking into account also the principles of statistical thermodynamics. An additional aim of the article is to emphasize the importance of elementary mathematical education for mastering the basic laws governing the course of physicochemical processes, as well as for true understanding of chemistry, in general

A modern look at electron configurations and the periodic table of elements, or relativistic effects in chemistry

The article describes in an accessible, conceptual way various types of relativistic effects, which are an important part of modern chemical education, practically absent in textbooks, however allowing for a better understanding of the properties of chemical elements and their compounds. This description was preceded by a concise non-relativistic characterization of electrons in multi-electron atoms, in terms of radial probability densities, in order to explain the dependence of electron energies on the principal (n) and orbital (l) quantum numbers. The results of recent quantum chemical calculations are discussed, which show the improved energy sequence of ns and (n-1)d orbitals in transition elements and explain the electron configurations of both neutral atoms and cations of the 3d and 4d block elements. The description of the relativistic effects begins with early Dirac concept of spin-orbit coupling as causing the splitting of the degenerate p, d and f orbitals for two sets of spinors. The role of this splitting in the stability of the respective oxidation states of the cations is discussed. Another important type of relativistic effects, confirmed only in the 1970s, operates in atoms of high nuclear charge (starting from 6. period) in which electrons move at a speed close to the speed of light. The resulting relativistic increase in the mass of the moving electron causes the stabilization of s and p orbitals, and destabilization of d and f orbitals. Representative examples of the influence of all relativistic effects on the properties of elements and their compounds are given (including mercury liquidity or the color of gold). In particular, relativistic effects specific for blocks 5d, 6p, 4f, 5f, 6d, and 7p were discussed. The possibilities of predicting further expansion of the periodic table with elements up to the atomic number of about 170 are outlined, based on taking into account both the relativistic effects for electrons and the stability of superheavy atomic nuclei. The article is addressed to chemists of all branches of this discipline

Editorial: Advances in Oscillating Reactions

Numerous processes in physical chemistry and related sciences take place in a cyclic fashion, with time-periodic variations in concentrations widely known as oscillatory or oscillating reactions

Thermokinetic Origin of Luminescent Traveling Fronts in the H₂O₂–NaOH–SCN^––Cu²⁺ Homogeneous Oscillator: Experiments and Model

According to our original discovery, the oscillatory course of the Cu²⁺-catalyzed oxidation of thiocyanate ions with hydrogen peroxide, in nonstirred medium and upon the addition of luminol as an indicator, can be a source of a novel type of dissipative patterns – luminescent traveling waves. The formation of these fronts, contrary to the patterns associated with the Belousov–Zhabotinsky reaction, cannot be explained in terms of coupled homogeneous kinetics and diffusion, and under isothermal conditions. Both experimental studies and numerical simulations of the kinetic mechanism suggest that the spatial progress of these waves requires mainly the temperature gradient in the solution, which affects the local chemical reaction rate (and thus the oscillation period), with practically negligible contribution from diffusion of reagents. As a consequence of this thermokinetic coupling, the observed traveling patterns are thus essentially the phase (or kinematic) waves, formed due to the spatial phase shift of the oscillations caused by differences in chemical reaction rates. The temperature gradient, caused by the significant heat effect of exothermic oxidation of thiocyanate by hydrogen peroxide, can emerge spontaneously as a local fluctuation or can be forced externally, if the control of progress of the luminescent waves is to be achieved