Atom conservation principle

The Atom Conservation Principle In a chemical reaction, the bonds of the initial molecules (called reactants ) are broken and remade to yield the final molecules, called the products. The chemical reaction is governed by the principle of conservation of the atom, which requires all chemical reactions to be balanced and have identical numbers of each atom on both sides of the equation arrow, as in Figure 2.5. 

The dependence on electron locahzation energy can also be illustrated by the use of the bond order conservation principle. This principle gives an approximate recipe to estimate changes in bond strength when coordination of a surface atom or adsorbate attachment changes [5, 15]. 

Naturally, the fixed composition phase transformations treated in this section can be accompanied by local fluctuations in the composition field. Because of the similarity of Fig. 17.3 to a binary eutectic phase diagram, it is apparent that composition plays a similar role to other order parameters, such as molar volume. Before treating the composition order parameter explicitly for a binary alloy, a preliminary distinction between types of order parameters can be obtained. Order parameters such as composition and molar volume are derived from extensive variables any kinetic equations that apply for them must account for any conservation principles that apply to the extensive variable. Order parameters such as the atomic displacement 77 in a piezoelectric transition, or spin in a magnetic transition, are not subject to any conservation principles. Fundamental differences between conserved and nonconserved order parameters are treated in Sections 17.2 and 18.3. 

Which of the following laws or principles immutability of atoms, conservation of mass, and Newton s laws, applies to each of the following phenomena ... 

One important conservation principle is provided by molecular theory atoms are conserved parcels of matter. (We ignore subatomic processes such as fission or fusion and consider only changes that do not modify the identities of atoms.) At the macroscopic level this conservation principle is the mass or material balance... 

The energy of adsorption on a surface atom increases with increasing coordinative unsaturation of the surface metal atom(s). This agrees with ideas proposed by the Bond Order Conservation Principle, which would indicate that the strength of the chemical bond increases when the number of atoms which share bonds to different adorbates decreases. 

Attractive or repulsive through-surface interactions are readily understood in terms of the Bond Order Conservation principles. When an adatom binds to a neighboring surface metal atom, the metal-metal bonds that form to the surface metal atom of interest are weakened. This increases the potential reactivity of the neighboring metal atoms since less of its electron density is tied to the metal atom involved in the surface-adatom bond. Thus, another adatom bound to the neighboring surface metal atom would have an increased interaction energy. Through-surface interactions are repulsive when two or more adsorbates share a metal atom, but attractive when the adsorbates sit at neighboring metal atom sites. These effects are illustrated in Fig. 3.54. 

When two (or more) adsorbed atoms bond to the same surface atom(s), they experience a repulsive interaction. When two adsorbed atoms bond to two different neighboring metal atoms that share a metal-metal bond, they tend to experience attractive interactions. These two rules can readily be deduced from the Bond Order Conservation principle which indicates that the atom-surface bond strength decreases with an increase in the number of adatoms bonded to the same surface metal atom. This change does not occur linearly with the number of neighboring atoms or molecules, but instead tends to vary exponentially. 

The activation energy for CO dissociation on rhodium is lower for the (100) than for the (111) surface. The (100) surface is the more open one of the two. Each rhodium atom misses four nearest neighbors in the first coordination shell as compared to a bulk atom, whereas an atom in the (111) surface misses three nearest neighbors. Hence, carbon and oxygen atoms bond more strongly with the (100) than with (111) surface and, similar to the situation in Figure 6.8, both thermodynamics and kinetics are more favorable for CO dissociation on the (100) surface. This is a manifestation of the bond order conservation principle The more the valence electrons of a metal atom at the surface become distributed in bonds with neighboring atoms, the weaker the individual bond becomes. 

The bond order conservation principle is conceptually useful but only approximately correct. Changes in ionization potential and electron affinity are also important and have to be included in more rigorous considerations. Nonetheless, to a first approximation changes in reactivity are primarily related to the coordination and geometry in the first coordination shell of surface atoms. 

The changes in distance illustrate the operation of the bond order conservation principle The more the electrons of an atom become distributed over bonds to neighboring atoms, the more each of these bonds weakens. 

However, general conservation principles of quantum mechanical wave mixing dictate that the final hybrids hj (Uke the atomic orbitals from which they originate) must be orthonormal ... 

In order to analyze flames and other reacting systems in terms of basic flow principles and chemical kinetics, it is necessary to consider the conditions in a differential control volume within the reacting fluid. To this control volume we must apply the four fundamental conservation principles which are the basis of all physical and chemical problems conservation of mass, momentum, energy, and atoms. For each of these, the fundamental continuity equation for a volume element states that the rate of accumulation of the quantity within the element is equal to the rate of gain due to flow plus the rate of gain due to reaction, i.e., for a quantity denoted by the subscript /c, and referring to unit volume... 

One molecule (or mole) of propane reacts with five molecules (or moles) of oxygen to produce three molecules (or moles) or carbon dioxide and four molecules (or moles) of water. These numbers are called stoichiometric coefficients (v.) of the reaction and are shown below each reactant and product in the equation. In a stoichiometrically balanced equation, the total number of atoms of each constituent element in the reactants must be the same as that in the products. Thus, there are three atoms of C, eight atoms of H, and ten atoms of O on either side of the equation. This indicates that the compositions expressed in gram-atoms of elements remain unaltered during a chemical reaction. This is a consequence of the principle of conservation of mass applied to an isolated reactive system. It is also true that the combined mass of reactants is always equal to the combined mass of products in a chemical reaction, but the same is not generally valid for the total number of moles. To achieve equality on a molar basis, the sum of the stoichiometric coefficients for the reactants must equal the sum of v. for the products. Definitions of certain terms bearing relevance to reactive systems will follow next. 

Atomic natural orbitals, use, 18 Attached processors FPS-164, 238-239 IBM hosts, 239 Aufbau principle, 51-52 Axial momentum, conservation of, CVD reactor, 337... 

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