Science & Mathematics

According to Lavoisier the physical sciences embody three important ingredients; facts, ideas, and language. Ideas had to be consistent with the facts generated from experiment and observation, and language needed to be precise and reflect the known chemistry of substances. Lavoisier had no time for what he termed theoretical speculation about the fundamental nature of matter and avoided the use of the atomic hypothesis or Aristotle’s elements in his Elements of Chemistry. In the preface to this famous work he claims he has good educational reasons for this position. This paper examines the extent to which Lavoisier kept to this agenda in his famous experiment on the composition of air and the implications of this for chemistry education are considered.

Analytical formulas are derived for integrals of the orbit‐orbit operator in the Breit‐Pauli Hamiltonian. The present method differs from an earlier one in the introduction of a new auxiliary function Gn(a) which is an integral of Shavitt's Fm(t) function. A method for its evaluation is discussed and some numerical examples are given. Copyright © 1975 John Wiley & Sons, Inc.

The study of free energy, enthalpy, and entropy changes accompanying the addition of substituted pyridines to iron(II) porphyrins has been extended to follow the effect of solvent change on these thermodynamic functions. Free energy changes are an unreliable index of strength of binding, but very large solvent effects are observed for enthalpy and entropy changes. Enthalpy effects were most favorable and entropy effects least favorable in carbon tetrachloride with decreasing magnitudes in chloroform and benzene. Statistical treatment of the results (62 data pairs) suggests that the contributions to these thermodynamic functions from different solvents, ligands, and metalloporphyrins operate independently and are additive. A linear model is proposed which simulates these effects. The thermodynamic data may be rationalized in terms of a relaxation in the binding of solvent molecules by heme when ligands are attached. The types of heme-solvent interaction occurring in the three solvents are different and solva.tion energies appear to decrease in the order benzene < chloroform < carbon tetrachloride. The associated large entropy changes follow the same order.

The presentation of gas properties in terms of the qualitative–quantitative mode and gas law sequence is examined by means of an analysis of 14 chemistry textbooks used in Australian secondary schools and of questionnaires on teaching approaches completed by 104 secondary science teachers. The findings indicate that current pedagogic practice involves minimal use of the qualitative relationships of the gas laws and moderate use of a simple‐to‐complex sequence. Given the conceptual complexity of the gas laws, the authors support a presentation approach with increased use of qualitative exercises and, in the initial stage at least, the use of a complex‐to‐simple model where the interrelationships among the gas laws are easier to establish. Copyright © 1993 Wiley.

CO₂ capture using aqueous ammonia is a potentially attractive option for emissions reductions from energy production and industrial processes. From an operational perspective, the capture absorbent must be monitored continuously to maintain the maximum efficiency of the capture process. In practice the composition of the absorbent is typically evaluated offline and retrospectively via wet chemistry methods, delaying any necessary variations to the process conditions to maintain maximum efficiency. Online absorbent monitoring methods incorporating spectroscopy via Raman or Fourier transform infrared (FT-IR) are attractive options due to their rapid response times and flexibility of the resulting output to be incorporated directly into process control packages. The present study outlines an evaluation of the FT-IR spectroscopic technique with analysis via partial least squares regression (PLSR) for a range of dilute to concentrated aqueous ammonia absorbents from ∼0.3–6.0 M and over a range of CO₂ loadings from ∼0.0–0.6 mol CO₂/mol NH₃. The water concentration in the samples ranges from ∼35.2–55.2 M. The effect of interfering SO_x species on the FT-IR method has been evaluated by incorporating dissolved SO₃^2– and SO₄^2– components into the solutions from 0.0–1.5 M. The analysis results in accurate concentrations for all analytes. The robustness of the analysis results has been evaluated and discussed. Additionally, FT-IR spectroscopy with PLSR was compared with conventional titration methods for a selected series of mixed NH₃/CO₂ standard solutions and a series of liquid samples from a bench-scale CO₂ absorption process. At low concentrations where the total NH₃ concentration is less than 4.0 M and the total CO₂ concentration is less than 1.5 M, both the combined PLSR with FT-IR method and the conventional potentiometric titration methods were suitable for the evaluation of the liquid compositions. However, at concentrations out of the low concentration range, the combined PLSR and FT-IR method was proven to have a robustness and accuracy greater than those of the conventional potentiometric titration methods. Therefore, given the simplicity and rapid turnaround of FT-IR spectroscopy in combination with PLSR, we consider this to be a superior and flexible technique for monitoring of CO₂ loaded aqueous ammonia solutions.

The introduction of a ‘co-reactant’ was a critical step in the evolution of electrogenerated chemiluminescence (ECL) from a laboratory curiosity to a widely utilised detection system. In conjunction with a suitable electrochemiluminophore, the co-reactant enables generation of both the oxidised and reduced precursors to the emitting species at a single electrode potential, under the aqueous conditions required for most analytical applications. The most commonly used co-reactant is tri-n-propylamine (TPrA), which was developed for the classic tris(2,2’-bipyridine)ruthenium(II) ECL reagent. New electrochemiluminophores such as cyclometalated iridium(III) complexes are also evaluated with this co-reactant. However, attaining the excited states in these systems can require much greater energy than that of tris(2,2’-bipyridine)ruthenium(II), which has implications for the co-reactant reaction pathways. In this tutorial review, we describe a simple graphical approach to characterise the energetically feasible ECL pathways with TPrA, as a useful tool for the development of new ECL detection systems.