by Jindřich Leitner and David Sedmidubský
Original Research
Much attention has been paid to thermodynamic modeling of nanosystems. A common approach consists in addition of a surface/interface term to the Gibbs energy of bulk materials and application of general conditions of equilibrium. Some discrepancy still remains dealing with the expression for surface contribution to molar Gibbs energy and chemical potential of components. It is shown, that due to the nonextensive nature of the surface area, these contributions are different for molar and partial molar quantities. The consistent expressions for the molar Gibbs energy and chemical potential of a single-component spherical nanoparticle are put forward along with the simple derivation of the Kelvin and Gibbs-Thomson equations.
World Journal of Chemical Education. 2017, 5(6), 206-209. DOI: 10.12691/wjce-5-6-4
Pub. Date: January 05, 2018
11082 Views2790 Downloads
by S. M. Blinder
Review Article
The structure and bonding of the hydrides of boron, carbon, nitrogen and oxygen are described using the concepts of the valence state and hybrid atomic orbitals. The tetrahedral arrangement of orbitals in CH4, NH3 and H2O is explained. A rationalization is proposed for the unique bridged structure of diborane B2H6.
World Journal of Chemical Education. 2017, 5(6), 203-205. DOI: 10.12691/wjce-5-6-3
Pub. Date: December 28, 2017
12900 Views1900 Downloads
by Alexander Roche, David Shoup and Rosemarie C. Chinni
Original Research
In this physical chemistry laboratory, the students develop experience in using Laser-Induced Breakdown Spectroscopy (LIBS) to analyze spectral emission data from to determine lifetimes of neutral and singly-ionized titanium species in LIBS plasmas. LIBS is a spectroscopic technique that focuses a high power laser on a surface. The laser heats, ablates, atomizes, and ionizes the surface material which creates a plasma. The light from the plasma is then spectrally resolved and detected. For LIBS experiments, the data can be collected using gated (using time delays and gate widths) or non-gated detection; this experiment uses gated detection taken at various time delays. The time delays used ranged from 0 to 60 μs to create the time decay curves. After creating the time decay curves for the titanium species used in this experiment, the students were able to examine the curves which illustrated the behavior of the neutral and singly-ionized titanium species and also gained experience calculating lifetimes.
World Journal of Chemical Education. 2017, 5(6), 197-202. DOI: 10.12691/wjce-5-6-2
Pub. Date: November 27, 2017
11307 Views2505 Downloads2 Likes
by Chad Rezsnyak
Original Research
The concepts of equilibrium and thermodynamics are among the most important topics covered in a general chemistry course. The thermodynamic properties ∆G°, ∆H°, and ∆S° are difficult to measure directly in a laboratory setting, but can be determined by monitoring the temperature dependence of the equilibrium constant, K. Previously published procedures require sophisticated technology or methodology, such as simultaneously measuring temperature and absorbance using a spectrophotometer, which may be unavailable to small and/or rural colleges and universities. Measuring the pH of a weak acid solution while varying the temperature allows for this analysis to be conducted simply, making it more accessible to broader range of academic laboratories. This experiment outlines the simple measurement of the equilibrium constant and temperature, with aspects of graphical analysis, allowing students to link the concepts of equilibrium and thermodynamics conceptually and mathematically. Calculated values of ∆G°298 are consistent with literature values, indicating that the experiment is suitably robust to be performed successfully by students of a wide range of skill levels.
World Journal of Chemical Education. 2017, 5(6), 193-196. DOI: 10.12691/wjce-5-6-1
Pub. Date: November 18, 2017
14844 Views3040 Downloads2 Likes