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Introduction
Published in Himadri Roy Ghatak, Reaction Engineering Principles, 2018
A chemical reaction is the phenomenon that transforms one chemical species into another. A chemical species is identified as a specific grouping of atoms joined together through interatomic forces or bonds, as they are called. Thus, a chemical reaction necessarily involves a rearrangement of atoms, that is, breaking of some of the existing chemical bonds and formation of some new ones. Chemical kinetics deals with the rapidness with which a chemical reaction can be carried out and the factors affecting this. It is common knowledge that not all the reactions proceed with the same rapidness. A solution of sodium hydroxide almost instantly reacts when brought in contact with a solution of hydrochloric acid. On the other hand, a broth of malt brews into alcohol over several days. It is obvious that if the changes are rapid, the desired outcome will be achieved in a short span of time and vice versa. The product quality and the rate of production from a chemical reaction are, therefore, interlinked and influenced by chemical kinetics. It will have a direct bearing on the profitability of the industry. The key factors affecting kinetics are temperature and concentration of reacting species. Another important factor is the presence of catalysts. This knowledge is essential for the engineer to design and operate reacting systems so that the chemical transformations are made to proceed to the desired extent in the least possible time.
Basic Concepts: Dynamics and Control of Chemical Reactions and Processes
Published in Victor H. Edwards, Suzanne Shelley, Careers in Chemical and Biomolecular Engineering, 2018
Victor H. Edwards, Suzanne Shelley
A mole is a mass of a chemical species that is numerically equal to the molecular weight of that species. For example, water has a molecular weight of 18, so a gram mole is 18 grams of water. A pound mole is 18 pounds of water. And so on.
Biochar effects on nitrous oxide and methane emissions from soil
Published in Johannes Lehmann, Stephen Joseph, Biochar for Environmental Management, 2015
Lukas Van Zwieten, Claudia Kammann, Maria Luz Cayuela, Bhupinder Pal Singh, Stephen Joseph, Stephen Kimber, Scott Donne, Tim Clough, Kurt A. Spokas
The processes of nitrification and denitrification are well-established redox reactions (Verstraete and Focht, 1977). Reduction occurs when a chemical species accepts an electron and oxidation occurs when electrons are donated from chemical species. An indication of the relative abundance of oxidized and reduced substances can be measured as a potential difference between an inert indicator electrode and a reference cell using a voltameter. The redox potential (Eh) is defined as the potential of an electrode consisting of a redox couple (e.g. SO42- and H2S) measured in a galvanic cell against the standard hydrogen electrode. Eh in soils generally ranges between 900mV and -300mV (Marcias and Camps-Arbestain, 2010) with water logged soils having Eh below 250–350mV (Kirk et al, 2003). Thermodynamic calculations have been carried out to determine the stability areas of the various chemical forms of an element in a solution as a composite function of Eh and pH. These are represented in Eh-pH or Pourbaix diagrams (Chesworth et al, 2006). In oxidized conditions (Eh> 500mV at pH 7), the thermodynamically stable form of N is NO3-, while lower redox conditions (Eh< 400mV at pH 7) and at a pH below 9.2, NH4+ will dominate. For an Eh of less than 0mV and pH of approximately 4 the stable form of gaseous C is CH4. As the pH increases there is a linear decrease in the Eh, the slope of which is dependent on the H+/e- ratio. For pH>6 and an Eh greater than 0mV the stable form of Fe is Fe3+ and when the pH is less than 6 the stable form of Fe is Fe2+ (Figure 17.3).
Novel concept for a filtered containment venting system with an ionic liquid to remove organic iodine (1)-proof of concept for organic iodine removal
Published in Journal of Nuclear Science and Technology, 2023
Sohei Fukui, Kazushige Ishida, Motoi Tanaka, Kazuo Tominaga
Verification results of the CH3I removal mechanism by [P66614][Cl] showed that [P66614][Cl] decomposed CH3I into methyl cation and iodide ion, and the resulting iodide ion was retained in the liquid state of [P66614][I] as shown in 2.3. The produced iodide ion may form an other chemical species and be volatilized from IL. The iodine release ratio to the supplied iodine was quantified and the DFT considering the organic and inorganic iodine release ratio was evaluated. Inorganic iodine species such as HI and I2 absorbed in the iodine trapping solution and adhered to the pipe inside surface were analyzed by ICP-MS. The results are summarized in Table 4. Three bottles filled with iodine trapping solution were installed, but iodide ions were detected only from the solution in the bottle placed in the uppermost stream. Therefore, the trap of iodide ions in the iodine trapping solution was sufficient. From the iodine concentration in the iodine trapping solution, the organic and inorganic iodine release ratio RTotal was calculated and RTotal was 1.9 × 10−4 (0.019%) which was a very small value. As a result, 99.98% of the CH3I supplied in the test was retained in the IL and the DFT calculated from the RTotal was more than 5000. This result assumed that even if the ratio of iodine released from IL was taken into consideration, the target performance of DF 50 or more was satisfied.
Computational and theoretical investigation of the geometrical structures, vibrational spectra and thermodynamic properties of the ionic and molecular clusters existing in vapours over strontium diiodide
Published in Molecular Physics, 2023
Association of small molecules and ions to form heavier ions has been the focus of many researchers recently [1–12]. The heavier ions mostly called cluster ions are characterised by noncovalent forces of two or more atoms or molecules of one or more chemical species with an ion [13]. These ions have attracted the interests of many researchers due to their unique electronic, optical and magnetic properties [14–16]. Due to these interesting properties, the cluster ions have been investigated and found to have potential applications in ion thrusters [17], ion implantation technologies [18], aerospace investigations [19,20] and in magnetohydrodynamic generators [21]. They have also been identified as potential building blocks of new materials and crystals [14–16], and can be used in chemical vapour transport and deposition [22–24]. Due to position of strontium in the periodic table, the ions existing in vapours over SrI2 dihalide are expected to have average or better properties making them potential for the stated applications above.
An intrinsic criterion of defining ionic or covalent character of AB-type crystals based on the turning boundary radii calculated by an ab initio method
Published in Molecular Physics, 2018
Dong-Xia Zhao, Chun-Yu Yan, Zun-Wei Zhu, Le Zhang, Yi-Ming Jiang, Rui Gong, Zhong-Zhi Yang
Our study provides a criterion of defining ionic or covalent character of AB-type crystals based on a new idea and calculated by ab initio method. For an AB-type crystal (supposing atom B is more electronegative than atom A), it is judged as an ionic crystal if the sum of A+ and B− radii is less than the practical separation between A and B in the crystal, and otherwise it is judged as a covalent crystal. This intuitive criterion brings a new feature into our knowledge and understanding about the ionic or covalent bonding character in a crystal. Of course, this criterion is not a deduction, but rather a semi-empirical summarisation based on the turning radii. Obviously, our criterion of judging their ionic or covalent character gives the same results as Pauling's for most of AB-type crystals, while some crystals, such as LiI and CuF, our criterion gives better indicator for this kind of ionic or covalent criterion for AB-type crystals than Pauling's. We are working to apply this criterion to judging the ionic or covalent nature of the multi-ionic crystals. Clearly, this approach can be extended to discuss the ionic or covalent nature of a chemical bond between any two chemical species.