Energy to break

Inspection of the values for the structure elements and their contribution to the heats of formation again allows interpretation The B-terms correspond to the energies to break these bonds, and a sequence of three carbon atoms introduces stabihty into an alkane whereas the arrangement of three carbon atoms around a central carbon atom leads to the destabilization of an alkane. 

Note however that Table 4 3 mcludes two entries for propane The second entry corresponds to the cleavage of a bond to one of the hydrogens of the methylene (CH2) group It requires slightly less energy to break a C—H bond m the methylene group than m the methyl group... 

The effective range of a typical air blaster is on the order of 1.8—2.4 m. If a single air blaster does not provide sufficient energy to break an arch, multiple units can be used. These are fired simultaneously if at the same elevation, then start sequentially from lower elevations in the hopper and work upward. 

Fiber Elongation, % Modulus, GPa " Strength, GPa Energy to break, /kg... 

Modern analytical pyrolysis has conventionally been canied out only by thermal energy to break some covalent bonds in the sample molecules at elevated temperatures to produce smaller and/or volatile fragments (pyrolyzates). On the other hand, the reactive pyrolysis in the presence of organic alkaline, such as tetramethylammonium hydroxide [(CH / NOH] (TMAH) has recently received much attention especially in the field of chai acterizing condensation polymers. 

Typical values of the energy to form vacancies are for silver, lOSkJmol and for aluminium, 65.5kJmol These values should be compared with the values for the activation enthalpy for diffusion which are given in Table 6.2. It can also be seen from the Table 6.2 that die activation enthalpy for selfdiffusion which is related to the energy to break metal-metal bonds and form a vacant site is related semi-quantitatively to the energy of sublimation of the metal, in which process all of the metal atom bonds are broken. 

On the other hand, if an amorphous polymer is struck above the Tg, i.e. in the rubbery state, large extensions are possible before fracture occurs and, although the tensile strength will be much lower, the energy to break (viz. the area under the curve) will be much more, so that for many purposes the material will be regarded as tough. 

Energy to break. This is quoted usually in joules or in ftlbf. The result will only apply to one set of sample dimensions and it is not possible to allow for any change in specimen dimensions. 

Energy to break per unit width of sample. (In notched specimens this is taken as the energy to break unit width of notch. In this case the results are quoted in such units as ft lb per inch of notch or joules per millimetre. The values obtained depend on the notch width. For example, it has been found that on reducing the notch width from V" to X the impact strength of a polycarbonate increased by a factor of 5.4 and that of unplasticised PVC by 3.1.)... 

The energy to break per fractured area. This will be the cross-sectional area of the sample less the area of the notch (as projected on the cross-section). The units used in this method are most commonly kJ/m, kgf cm cm and ft Ibfin . These are related by the factors... 

If it is considered, in the first instance, that the distribution is energy controlled and not diffusion controlled, a solute molecule will desorb from the stationary phase when it randomly has sufficient kinetic energy to break its association with a molecule of stationary phase, as discussed in chapter 1. Similarly, a molecule will be absorbed under the same conditions. 

Occasionally the less satisfactory term of energy to break per unit width may be quoted in units of J/m. 

The tensile strengths are about 55 MN/m, the elongations at break usually less than 10% and the modulus of elasticity about 2-7 GN/m Since the area under the curve provides a measure of the energy required to break the bonds, and since this area is small such polymers will have a low impact strength (which is closely related to energy to break) and will break with a brittle fracture. 

A phase change in which the molecules become further separated, such as vaporization, requires energy to break intermolecular attractions and is therefore endothermic. Phase changes that increase molecular contact, such as freezing, are exothermic because energy is given off when attractions form between molecules. 

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]... 

The most efficient turbulent eddies for bubble breakup are eddies of the same size as the bubbles. Large eddies will merely move the bubbles and smaller eddies do not have sufficient energy to break up the bubbles. Assuming that the most efficient eddies to break up fluid particles are eddies of the same size as the bubble, that is, A. 2d, gives the required turbulent energy dissipation... 

Ultraviolet photons have enough energy to break chemical bonds. When UV light breaks bonds in biochemical molecules, the products can undergo chemical reactions that lead to cell damage. 

The addition of solutes decreases the freezing point of a solution. In the solution, solvent molecules collide with crystals of solid solvent less frequently than they do in the pure solvent. Consequently, fewer molecules are captured by the solid phase than escape from the solid to the liquid. Cooling the solution restores dynamic equilibrium because it simultaneously reduces the number of molecules that have sufficient energy to break away from the surface of the solid and increases the number of molecules in the liquid with small enough kinetic energy to be captured by the solid. 

A stabie moiecuie such as N2 O4 does not decompose unless it first acquires the energy needed to break one of its bonds. Recall from Section 6- that any collection of molecules has a distribution of kinetic energies. Molecular collisions can convert kinetic energy of one molecule into vibrational energy of another molecule, giving some molecules enough energy to break apart. 

In a vessel that contains only NO2 molecules, the production of N2 O4 is the only reaction that takes place. However, once N2 O4 molecules are present, the reverse reaction also can occur. An N2 O4 molecule can fragment after collisions give It sufficient energy to break the N—N bond. These fragmentations regenerate NO2 N2 O4 2 NO2... 

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