Reviewing Some Crucial Concepts of Gibbs Energy in Chemical Equilibrium Using a Computer-Assisted, Guided-Problem-Solving Approach

Abstract

G, G°, Δ r G, Δ r G°, ΔG, and ΔG°are essential quantities to master the chemical equilibrium. Although the number of publications devoted to explaining these items is extremely high, it seems that they do not produce the desired effect because some articles and textbooks are still being written with some of these quantities that appear to be identical to others. This work attempts to clarify the differences between the six quantities using a guidedproblem-solving approach instead of a more conventional expository style. A very simple chemical equilibrium, N 2 O 4 (g) ⇌ 2NO 2 (g), has been chosen as an example. Furthermore, it has been treated in the simplest possible way (as an ideal gas mixture, to thereby avoid fugacities), because the important issue is to sort out concepts and not get entangled in laborious calculations that many times obscure the didactic objective pursued. It is complemented with a small computational tool (a MATLAB script) to quickly perform calculations and graphs. In addition, the script allows one to analyze interactively (through a user-friendly interface) the disturbances that occur in chemical equilibrium owing to changes in temperature and pressure. An exhaustive review of the literature has also been made to select the most useful sources to study this problem.

Geometrical Description of Chemical Equilibrium and Le Châtelier’s Principle: Two-Component Systems

“…Representations of chemical equilibrium often do not involve graphical presentations. Some representations showing the dependence of the amounts of individual reaction components on the extent of reaction or the relationship between thermodynamic functions have been described in chemical education literature. , Graphical representations are useful to students because they visualize functional dependences among the parameters that describe the system, especially if these dependencies are nonlinear. The graphical description of chemical equilibrium, quantitative analysis of Le Châtelier’s principle, and explicit introduction of conservation of mass is, to the best of the author’s knowledge, novel.…”

A Discrete Approximation to Gibbs Free Energy of Chemical Reactions is Needed for Accurately Calculating Entropy Production in Mesoscopic Simulations

“…When the copy numbers of the chemical species are treated as continuous, there is no notion of a single occurrence of a reaction; instead the evolution of the system is parameterized by the continuous variable ξ which quantifies the extent of advancement of the reaction [30]. In this framework, which is adopted in classical thermodynamics, the copy number of any species never jumps instantaneously from N i to N i + ν i , and thus the premise of the derivation presented above leading to Equation 16 falls apart.…”

Unconstrained Gibbs minimization for solving multireaction chemical equilibria using a stochastic global optimizer

“…2 NO 2 at 1 bar and 298.15 K. Initially, 1 mol of N 2 O 4 is present. Gibbs free energy of formation at 298.15 K was obtained from Borge [3]. The three matrices needed to start the calculation are A ¼ [2 4], F ¼ [2 4; 1 2], and GRT ¼ [39.4489 20.6783].…”

“…Systems involving one reaction only are generally easy to solve. For example, Borge illustrated the use of the different calculation methods to solve a simple example [3]. Tellinghuisen [4] illustrated the use of the equilibrium constant in solving a simple chemical equilibrium problem for an ammonia synthesis reaction.…”