Closed Systems without Chemical Reactions

2020 ◽  
pp. 31-123
Keyword(s):  
Chemical Reactions ◽  
Closed Systems

Oscillatory chemical reactions in closed vessels

1986 ◽  
Vol 406 (1831) ◽  
pp. 299-323 ◽  
Keyword(s):  
Chemical Reactions ◽  
Kinetic Scheme ◽  
Order Process ◽  
Large Excess ◽  
Initial Value ◽  
First Order ◽  
Slow Decay ◽  
Stable Product ◽  
Oscillatory Chemical ◽  
Closed Systems

A skeleton kinetic scheme representing the simplest model for oscillatory chemical reactions in a closed vessel can be built around an autocatalytic feedback step precursor decay P → A k 0 p , uncatalysed step A → B k 3 a , autocatalysis A + 2B → 3B k 1 ab 2 , catalyst decay B → C k 2 b . The first intermediate A is formed via the slow decay of a reactant or precursor species P, initially in large excess. A is converted to B via two routes: a slow pseudo-first order process and a step in which B acts as its own catalyst. The autocatalyst B is then capable of a simple first order decay to a stable product C. The concentrations of the various species at first change steadily, with that of P decreasing while A, B and C increase. This period is followed by the onset and growth of oscillations in the concentrations of the intermediates A and B. The behaviour at long times, depends upon the uncatalysed conversion of A to B. Provided k 3 is not taken as zero, the oscillations finally diminish in amplitude and die out leaving a steady decay of P, A and B until everything has been converted to C. The simplicity of the model allows the first self-consistent test of the ‘pool chemical approximation’, an approach commonly used in the analysis of mechanisms in closed systems in which the precursor concen­tration is assumed to be constant and set equal to its initial value. The results presented here reveal the range of applicability of the approxi­mation and show clearly how and why it can break down to give un­physical predictions.

scholarly journals Entropy Production in Simple Chemical Reactions

1975 ◽  
Vol 53 (12) ◽  
pp. 1756-1760 ◽  
Author(s):  
Huw O. Pritchard
Keyword(s):  
Entropy Production ◽  
Constant Temperature ◽  
Chemical Reactions ◽  
Species Number ◽  
Completely Monotonic Function ◽  
Completely Monotonic ◽  
Simple Chemical ◽  
Closed Systems ◽  
Oscillatory Processes ◽  
Monotonicity Principle

It is shown that entropy production appears to be a completely monotonic function of time for several chemical reactions or reaction sequences taking place in closed systems at constant temperature; however this monotonicity principle does not extend to autocatalytic or oscillatory processes. Where it occurs, the complete monotonicity of entropy production stems essentially from the completely monotonic behavior of the species number densities as functions of time in the evolution of the reaction.

scholarly journals Review of Reactors with Potential Use in Thermochemical Energy Storage in Concentrated Solar Power Plants

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2358 ◽  
Author(s):  
Gabriel Zsembinszki ◽  
Aran Solé ◽  
Camila Barreneche ◽  
Cristina Prieto ◽  
A. Fernández ◽  
...  
Keyword(s):  
Energy Storage ◽  
Chemical Reactions ◽  
Power Plants ◽  
Solar Power ◽  
Fixed Bed ◽  
Fixed Bed Reactor ◽  
Concentrated Solar Power ◽  
Solar Power Plants ◽  
Closed Systems ◽  
Concentrated Solar Power Plants

The aim of this study is to perform a review of the state-of-the-art of the reactors available in the literature, which are used for solid–gas reactions or thermal decomposition processes around 1000 °C that could be further implemented for thermochemical energy storage in CSP (concentrated solar power) plants, specifically for SPT (solar power tower) technology. Both direct and indirect systems can be implemented, with direct and closed systems being the most studied ones. Among direct and closed systems, the most used configuration is the stacked bed reactor, with the fixed bed reactor being the most frequent option. Out of all of the reactors studied, almost 70% are used for solid–gas chemical reactions. Few data are available regarding solar efficiency in most of the processes, and the available information indicates relatively low values. Chemical reaction efficiencies show better values, especially in the case of a fluidized bed reactor for solid–gas chemical reactions, and fixed bed and rotary reactors for thermal decompositions.

Review Lecture - Instabilities and oscillations in chemical reactions in closed and open systems

1988 ◽  
Vol 415 (1848) ◽  
pp. 1-34 ◽  
Keyword(s):  
Chemical Reactions ◽  
Open Systems ◽  
Homogeneous Systems ◽  
Self Consistent ◽  
Closed Systems ◽  
The Law ◽  
Physical Principles

This lecture is chiefly concerned with isothermal oscillations in homogeneous systems, and with finding and validating self-consistent models. Emphasis is laid on satisfying basic physical principles and on preserving chemical reasonableness in as simple a manner as possible. The goal is to devise a scheme that can be applied to a wide variety of circumstances to predict new behaviour as well as to interpret what is known, and to form a foundation for later developments and elaborations. This core of the scheme, called the autocatalator, combines an autocatalytic step A + 2B → 3B, rate = k 1 ab 2 , with catalyst decay B → C, rate = k 2 b . These core reactions may display reversibility and they may be accompanied by uncatalysed conversion A → B, rate = k u a . Particular stress is given to the problem of closed systems. In closed systems, oscillations cannot be indefinitely sustained. In former days it was customary to ignore this inconvenience (and to repeal the law of conservation of matter); today a less unsatisfactory account is possible.

Surface reactions observed by photoemission electron microscopy (PEEM)

1992 ◽  
Vol 50 (1) ◽  
pp. 286-287
Author(s):  
H.H. Rotermund
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Work Function ◽  
Chemical Reactions ◽  
Reaction Diffusion ◽  
Dynamic Processes ◽  
Clean Surface ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Photoemission Electron

Chemical reactions at a surface will in most cases show a measurable influence on the work function of the clean surface. This change of the work function δφ can be used to image the local distributions of the investigated reaction,.if one of the reacting partners is adsorbed at the surface in form of islands of sufficient size (Δ>0.2μm). These can than be visualized via a photoemission electron microscope (PEEM). Changes of φ as low as 2 meV give already a change in the total intensity of a PEEM picture. To achieve reasonable contrast for an image several 10 meV of δφ are needed. Dynamic processes as surface diffusion of CO or O on single crystal surfaces as well as reaction / diffusion fronts have been observed in real time and space.

Microwaves: Application in Electron Microscopy

1990 ◽  
Vol 48 (3) ◽  
pp. 140-141
Author(s):  
Anthony S-Y Leong ◽  
David W Gove
Keyword(s):  
Electron Microscopy ◽  
Light Microscopy ◽  
Chemical Reactions ◽  
Electromagnetic Waves ◽  
Tissue Fixation ◽  
Primary Method ◽  
Dipolar Molecules ◽  
Wide Range ◽  
Time Required ◽  
Cryostat Sections

Microwaves (MW) are electromagnetic waves which are commonly generated at a frequency of 2.45 GHz. When dipolar molecules such as water, the polar side chains of proteins and other molecules with an uneven distribution of electrical charge are exposed to such non-ionizing radiation, they oscillate through 180° at a rate of 2,450 million cycles/s. This rapid kinetic movement results in accelerated chemical reactions and produces instantaneous heat. MWs have recently been applied to a wide range of procedures for light microscopy. MWs generated by domestic ovens have been used as a primary method of tissue fixation, it has been applied to the various stages of tissue processing as well as to a wide variety of staining procedures. This use of MWs has not only resulted in drastic reductions in the time required for tissue fixation, processing and staining, but have also produced better cytologic images in cryostat sections, and more importantly, have resulted in better preservation of cellular antigens.

Fine structure and properties of defects in naturally occurring silicates and oxides

1990 ◽  
Vol 48 (4) ◽  
pp. 460-461
Author(s):  
David R. Veblen
Keyword(s):  
Chemical Reactions ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Single Chain ◽  
Naturally Occurring ◽  
Resolution Electron ◽  
Fine Structures ◽  
Image Simulations ◽  
Similar Crystal Structure

Extended defects and interfaces control many processes in rock-forming minerals, from chemical reactions to rock deformation. In many cases, it is not the average structure of a defect or interface that is most important, but rather the structure of defect terminations or offsets in an interface. One of the major thrusts of high-resolution electron microscopy in the earth sciences has been to identify the role of defect fine structures in reactions and to determine the structures of such features. This paper will review studies using HREM and image simulations to determine the structures of defects in silicate and oxide minerals and present several examples of the role of defects in mineral chemical reactions. In some cases, the geological occurrence can be used to constrain the diffusional properties of defects.The simplest reactions in minerals involve exsolution (precipitation) of one mineral from another with a similar crystal structure, and pyroxenes (single-chain silicates) provide a good example. Although conventional TEM studies have led to a basic understanding of this sort of phase separation in pyroxenes via spinodal decomposition or nucleation and growth, HREM has provided a much more detailed appreciation of the processes involved.

Gum Arabic in Chemical Reactions

1883 ◽  
Vol 15 (366supp) ◽  
pp. 5844-5844
Author(s):  
MM. Jules Lefort ◽  
P. Thibault
Keyword(s):  
Chemical Reactions ◽  
Gum Arabic
Sign in / Sign up

Export Citation Format

Share Document