Chemical equations molecular representations

The three representations that are referred to in this study are (1) macroscopic representations that describe the bulk observable properties of matter, for example, heat energy, pH and colour changes, and the formation of gases and precipitates, (2) submicroscopic (or molecular) representations that provide explanations at the particulate level in which matter is described as being composed of atoms, molecules and ions, and (3) symbolic (or iconic) representations that involve the use of chemical symbols, formulas and equations, as well as molecular structure drawings, models and computer simulations that symbolise matter (Andersson, 1986 Boo, 1998 Johnstone, 1991, 1993 Nakhleh Krajcik, 1994 Treagust Chittleborough, 2001). 

The capacity to construct a representation in any appropriate mode and submode for a given purpose. For example, being able to represent the working of an oil refinery in terms of a diagram of its component parts to an explanation of what takes place in terms of molecular transformations and the chemical equations for these ... 

Butlerov s prophecy has been taken as heralding the first step toward the creation of molecular representations with which all chemical properties of a substance could be rationalized. Some imagine these to be iconic formulas of a "photographic" fidelity. Others assert that the ultimate representation of a chemical substance is a mathematical equation—the molecular wavefunction—that would permit not only the rationalization but even the prediction of the material s chemical behavior (Mosini, 1994). One of my theses is that no such single "rational formula" exists or could exist. However, exploring why Butlerov s vision is unrealizable can shed light on what entities chemists see as "fundamental" and the role of time within chemistry. 

Note that the stoichiometric coefficients in a balanced chemical equation like eq. (2.5) bear no necessary relationship to the orders that appear in the empirical (i.e., experimentally derived) rate law. This statement becomes obvious if one considers that the chemical equation can be multiplied on both sides by any arbitrary number and remain an accurate representation of the stoichiometry even though all the coefficients will change. However, the orders for the new reaction will remain the same as they were for the old one. There are cases in which the rate law depends only on the reactant concentrations and in which the orders of the reactants equal their molecularity. A reaction in which the order of each reactant is equal to its molecularity is said to obey the Law of Mass Action or to behave according to mass action kinetics. 

Balance the numbers of atoms of each kind on both sides of the expression to obtain a balanced chemical equation. In this step, the coefficient 2 is placed in front of the formulas NO and NO2. This means that two molecules of NO are consumed and two molecules of NO2 are produced for every molecule of O2 consumed. In the balanced equation there are two N atoms and four O atoms on each side. In a balanced equation, the total number of atoms of each element present is the same on both sides of the equation. We see this below, both in the symbolic equation and in the molecular representation of the reaction. 

The major part of this article will be devoted to a particular class of reaction systems—namely, monomolecular systems. A reaction system of (n) molecular species is called monomolecular if the coupling between each pair of species is by first order reactions only. These linear systems are satisfactory representations for many rate processes over the entire range of reaction and are linear approximations for most systems in a sufficiently small range. They play a role in the chemical kinetics of complex systems somewhat analogous to the role played by the equation of state of a perfect gas in classical thermodynamics. Consequently, an understanding of their behavior is a prerequisite for the study of more general systems. 

Operator equations have been employed by George and Ross (1971) to analyse symmetry in chemical reactions. In order to preserve the identity of electronic states of reactants and products, these authors worked within a quasi-adiabatic representation of electronic motions. By introducing a chain of approximations, going from separate conservation of total electronic spin to complete neglect of dynamics, they discussed the Wigner-Witmer angular momentum correlation rules, Shuler s rules for linear molecular conformations and the Woodward-Hoffmann rules. 

In the present chapter, we have reviewed our recent efforts to combine experimental and theoretical efforts to refine our knowledge of interatomic potentials and chemical processes at extreme conditions of pressure and temperature. We have demonstrated using selected molecular systems that our equation of state model can be used to accurately predict properties of non-polar and polar fluids including fluid mixtures. The accuracy of the equation of state of polar fluids is significantly enhanced by using a multi-speeies or cluster representation of the fluid. 

The AIM chemical potentials defined by the partial functional derivatives of equation (35), calculated for the fixed external potential and the frozen embedding densities pp a r) of the remaining subsystems, are equalized only when the subsystems are mutually open [4,5], This is the case in the global equilibrium state considered in the preceding section. In what follows we shall denote such open subsystem condition by the vertical broken fines in the symbolic representation of the molecular system as a whole, Mg = (a fi y. ..), in the global (g, intersubsystem) equilibrium of the ground-state of an externally open system ... 

Permeability coefficients may be affected by chemical properties other than log and MW. For example, steric interactions, limitations of MW as a representation of molecular size, and unidentified factors that cause some compounds to act as penetration enhancers may affect permeability coefficients but would not be conveyed entirely by log and MW. Equation 15.7 will not account for these additional influences on permeability coefficients. However, the error in Equation 15.8 may be reduced compared with Equation 15.7, because Equation 15.8 is based on the animal-to-human ratio of permeabihty values. Equation 15.7 implicitly assumes that permeability coefficients are affected by log and MW only, which is a more restrictive assumption than the assumption built into Equation 15.8 that all unexplored factors have quantitatively the same effect in all species. That is, with the same amount of data, analysis with Equation 15.8 is preferable to analysis with Equation 15.7 as long as these additional factors influence permeability coefficients the same way in both human and animal skins. 

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