Bond breaking Bonding, chemical

The calorimetrically measured AH is usually assigned to the fonnation and breaking of chemical bonds. The equation... 

Since a critical strain-rate (sf) must be surpassed to break the chemical bond, only macromolecules flowing close to the central streamline could be degraded near the scission threshold. Another streamline passing through the orifice at a distance r from the symmetry axis will reach the required strain rate at a higher fluid velocity (Fig. 35) in order to meet the condition ... 

In photo CVD, the chemical reaction is activated by the action of photons, specifically ultraviolet (UV) radiation, which have sufficient energy to break the chemical bonds in the reactant molecules. In many cases, these molecules have a broad electronic absorption band and they are readily excited by UV radiation. Although UV lamps have been used, more energy can be obtained from UV lasers, such as the excimer lasers, which have photon energy ranging from 3.4 eV (XeF laser) to 6.4 eV (ArF laser). A typical photo-laser CVD system is shown schematically in Fig. 5.14.117]... 

Conventional presentaticsis of DFT start with pure states but sooner w later encounter mixed states and d sities (ensemble densities is the usual formulation in the DFT literature) as well. These arise, for example in formation or breaking of chemical bonds and in treatments of so-called static correlation (situations in which several different one-electron configurations are nearly degenerate). Much of the DFT literature treats these problems by extension and generalization from pure state, closed shell system results. A more inclusively systematic treatment is preferable. Therefore, the first task is to obtain the Time-Dependent Variational Principle (TDVP) in a form which includes mixed states. 

This energy change is positive because the chemical system gains the energy required to break the chemical bonds. 

C07-0098. It requires 364 kJ/mol to break the chemical bond in HBr molecules. What is the longest wavelength (in nm) of light that has enough energy to cause this bond to break Will HBr molecules in the troposphere be fragmented into atoms ... 

As described in Section 6-, energy must be supplied to break any chemical bond. Bond energies, like bond lengths, vary in ways that can be traced to atomic properties. There are three consistent trends in bond strengths ... 

Network solids such as diamond, graphite, or silica cannot dissolve without breaking covalent chemical bonds. Because intermolecular forces of attraction are always much weaker than covalent bonds, solvent-solute interactions are never strong enough to offset the energy cost of breaking bonds. Covalent solids are insoluble in all solvents. Although they may react with specific liquids or vapors, covalent solids will not dissolve in solvents. 

V.I. Vedeneev, L.V. Gurvich, V.N. Kondratyev, et al.. Handbook of Energies of Breaking of Chemical Bonds. Ionization Potential and Electron Attachment Energies, Kondratyev,V.N. (ed.), USSR Acad, of Sci. Publ., Moscow, 1962 (in Russian). 

It permanently destroys toxic organic compounds contained in hazardous waste by breaking their chemical bonds and reverting them to their constituent elements, thereby reducing... 

Within the framework of the Bom-Oppenheimer approximation, a diatomic molecule consists of two nuclei that are more-or-less attached by the surrounding electron cloud. Often the specific form of the resulting potential function is not known. However, if a chemical bond is formed between the two nuclei, the potential function displays a minimum at a distance that corresponds to the equilibrium bond length. Furthermore, the energy necessary to break the chemical bond, the dissociation energy, is often evaluated by spectroscopic measurements. It can be concluded, then, that the potential fiinction has the general form shown in Fig. 6. A simple derivation of the Born- Qppenheimer approximation is presented in Section 12.1. 

The collision must be sufficiently energetic that enough energy is available to break the chemical bond linking the two bromine atoms. This type of reaction is called an initiation reaction because it generates a species that can serve as a chain carrier or active center in the following sequence of elementary reactions. 

Since chemical reactions involve the making and breaking of chemical bonds with their associated energy effects and geometric requirements, it is not unreasonable to assume that these factors play an important role in determining the probability that a bimolecular collision will lead to chemical reaction. In addition to these factors there are restrictions on bimolecular combination or association reactions and quantum mechanical requirements that can influence this probability. 

At 2000 K there is sufficient energy to make the H2 molecules dissociate, breaking the chemical bond the core density is of order 1026 m-3 and the total diameter of the star is of order 200 AU or about the size of the entire solar system. The temperature rise increases the molecular dissociation, promoting electrons within the hydrogen atoms until ionisation occurs. Finally, at 106 K the bare protons are colliding with sufficient energy to induce nuclear fusion processes and the protostar develops a solar wind. The solar wind constitutes outbursts of material that shake off the dust jacket and the star begins to shine. 

The state of matter within these regions needs to be determined before the balance of energy and chemistry can be understood. Extreme photon fluxes break all chemical bonds, prevent molecule formation and ionise atoms but as the density of species increases the UV and far-UV photons are absorbed and molecules begin to form. Chemical reactions are, however, slow in the gas phase due to the low temperature, and molecules condense out on the surface of dust particles, perhaps forming ice grains. Once on the surface, molecules continue to be photoprocessed by the starlight as well as by the continual bombardment of cosmic rays. 

The breaking of chemical bonds initiated by photons may be written, for example... 

Chemistry within the body is approximately five times faster than in a test tube at room temperature. The reverse is true, of course, with chemical reactions in liquid methane at 100 K some 1.2 x 1035 times slower than at 298 K. Neutral chemical reactions remain slow in solution at 100 K if they have a significant activation barrier. As with the ISM, chemistry involving breaking of chemical bonds is frozen out at 100 K and has direct implications for chemistry on the surface of Titan, for example. 

Bond energy The energy required to break a chemical bond and pull a molecule apart. 

Enzymes do chemistry. Their role is to make and break specific chemical bonds of the substrates at a faster rate and to do it without being consumed in the process. At the end of each catalytic cycle, the enzyme is free to begin again with a new substrate molecule. 

Most of the oxygen injected into a gasifier, either as pure oxygen or air, is consumed in reactions (1) through (3) to provide the heat necessary to dry the solid fuel, break up chemical bonds, and raise the reactor temperature to drive gasification reactions (4) through (9). 

Finally, as a simple illustration of how weak these forces are, note how the energy required to break the hydrogen bonds in liquid hydrogen chloride (i.e. the energy required to vaporize it) is 16 kJmol-1, yet the energy needed break the chemical bond between atoms of hydrogen and chlorine in H-Cl is almost 30 times stronger, at 431 kJmol-1. 

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