Rate of destruction

The rate of destruction of active sites and pore structure can be expressed as a mass-transfer relation for instance, as a second-order reaction... 

If C is a reactive, unstable species, its concentration will never be very large. It must then be consumed at a rate that closely approximates the rate at which it is formed. Under these conditions, it is a valid approximation to set the rate of formation of C equal to its rate of destruction ... 

In some cases, the principal interest is in the possibility of undesired contamination or other alteration of an environment rather than in the rate of destruction of the metals being tested. Here, in addition to paying attention to the usual factors that influence rates of corrosion, it is necessary also to consider the ratio of the area of the test specimen to the volume or mass of test solution, and the time of contact. All of these factors may be quite different in a test from what would obtain in a practical case, and any dis-... 

The kinetics of culture media sterilisation describe the rate of destruction of microorganisms by steam using a fust-order chemical reaction rate model. As the population of microorganisms (N) decreases with time, the rate is defined by the following equation ... 

In order to calculate the steady-state concentration of ozone in the stratosphere, we need to balance the rate of production of odd oxygen with its rate of destruction. Chapman originally thought that the destruction was due to the reaction O + 03 —> 2O2, but we now know that this pathway is a minor sink compared to the catalytic destruction of 03 by the trace species OH, NO, and Cl. The former two of these are natural constituents of the atmosphere, formed primarily in the photodissociation of water or nitric oxide, respectively. The Cl atoms are produced as the result of manmade chlorofluorocarbons, which are photodissociated by sunlight in the stratosphere to produce free chlorine atoms. It was Rowland and Molina who proposed in 1974 that the reactions Cl + 03 —> CIO + O2 followed by CIO + O —> Cl + O2 could act to reduce the concentration of stratospheric ozone.10 The net result of ah of these catalytic reactions is 2O3 — 3O2. 

This reaction is very exothermic (A// —180 to —200kJ mol-1) and, therefore, seems to be very probable from the thermochemical point of estimation. The pre-exponential factor is expected to be low due to the concentration of the energy on three bonds at the moment of TS formation (see Chapter 3). To demonstrate that this reaction is responsible for the oxidative destruction of polymers, PP and PE were oxidized in chlorobenzene with an initiator and analyzed for the rates of oxidation, destruction (viscosimetrically), and double bond formation (by the reaction with ozone) [131]. It was found that (i) polymer degradation and formation of double bonds occur concurrently with oxidation (ii) the rates of all three processes are proportional to v 1/2, (iii) independent of p02, and (iv) vs = vdbf in PE and vs = 1.6vdbf in PP (vdbf is the rate of double bond formation). Thus, the rates of destruction and formation of double bonds, as well as the kinetic parameters of these reactions, are close, which corroborates with the proposed mechanism of polymer destruction. Therefore, the rate of peroxyl macromolecules degradation obeys the kinetic equation ... 

To understand how an appropriate momentum equation can be derived, consider first a stationary tank into which solid masses are thrown, Figure 1.7a. Momentum is a vector and each component can be considered separately here only the x-component will be considered. Each mass has a velocity component vx and mass m so its x-component of momentum as it enters the tank is equal to mvx. As a result of colliding with various parts of the tank and its contents, the added mass is brought to rest and loses the x-component of momentum equal to mvx. As a result there is an impulse on the tank, acting in the x-direction. Consider now a stream of masses, each of mass m and with a velocity component vx. If a steady state is achieved, the rate of destruction of momentum of the added masses must be equal to the rate at which momentum is added to the tank by their entering it. If n masses are added in time t, the rate of addition of mass is nmJt and the rate of addition of x-component momentum is (nm/t)vx. It is convenient to denote the rate of addition of mass by Af, so the rate of addition of x-momentum is Mvx. 

Below a certain pressure, the reaction takes place slowly and smoothly. At low pressure, the active species or radicals reach the surface easily and get destroyed. The rate of destruction of radicals counter balances the increase of formation of radicals from branching of the chain. Hence, the reaction proceeds smoothly. 

On increasing the pressure, the rate of diffusion of the radicals to the walls decreases and therefore the rate of destruction of radicals also slows down while the rate of propagation and branching increases. Thus due to a considerable rise in concentration of radicals the rate of reaction increases enormously leading to an explosion. This is called lower explosion limit and depends upon the size and shape of the vessel. 

If the destruction is observant from the initial value of molecular mass M0 to a certain finite value Moo, then at point of time t the chain group with molecular mass M0 - Mt (where Mt is the average value of molecular mass at a given point of time) is involved in the process. It is natural to assume that the rate of destruction in a unit time is proportional to the whole... 

When radical A- reacts to form product radical B- with an appropriate rate constant, the absolute concentrations of each radical can be determined in a steady-state ESR experiment. This ratio and a measured or calculated rate of destruction of A- and B- by diffusion-controlled radical-radical reactions can be used to calculate the rate constant for formation of B-from A-. 

In the LANL experiments, all of the energetic material was introduced into the vessel at the beginning of the run, when the caustic was still at ambient temperature in the HAAP runs, the caustic was heated to the reaction temperature before the energetic feed was introduced. Therefore, the rate of destruction from the LANL data is not comparable to that from the HAAP data. It appears that the evolution of gas commenced at about 65-70°C for both Composition B-4 in 20 percent caustic and tetrytol in 12 percent caustic. No temperature data were presented for Composition B-4 in 15 percent caustic, and tetrytol appeared to begin generating gas at a somewhat higher temperature ( 80°C) in 20 percent caustic. 

The coulombic efficiencies for the destruction were calculated to be as follows (figures in parentheses include the total rate of destruction when direct chemical oxidation by HN03 is included) ... 

Consider briefly the disease gout, which is characterized by the precipitation of urates in tissues and by the presence of hyperuricemia. Bauer and Klemperer state, 11 "The etiology of the disease is unknown." As has been pointed out by other writers, the presence of high concentrations of uric acid in the blood may be due to (1) overproduction, (2) lowered excretion, (3) lowered destruction, or, of course, any combination of the three. Let us consider two hypothetical individuals, A and B, 30 years of age who have exactly the same uric acid blood level (4 mg. per cent) and exactly the same amount of blood (8 liters). The total uric acid in their respective bloods is 320 mg. Let us suppose further that the rate of production of uric acid in the two individuals is continuously exactly the same, the rate of destruction in the two is continuously the same, and that they consume exactly the same food. One hypothetical individual, A, however, continuously excretes on the average 0.1 mg. less uric acid per day than the other. This is very little, compared with the usual total excretion of 700 mg. per day. In the course of 10 years, A s uric acid blood level will, however, have more than doubled, due to this increased retention, and he will be in the range of "gouty" as contrasted with "normal" individuals. This could happen by a very gradual increase, in one individual, of the renal threshold for uric acid. Whether excretion, production, or destruction is responsible for the difference between individuals, the total accumulation of uric acid in hyperuricemia is small. 

Prior to the degradation of many organic compounds, a period is noted in which no destruction of the compound is evident. This time interval is designated as an acclimation period or, sometimes, an adaptation or lag period [93-98]. It may be defined as the length of time between the addition or entry of the compound into an environment and evidence of its detectable loss. During this interval, no change in concentration is noted, but then the disappearance becomes evident and the rate of destruction often becomes rapid. 

A flame is quenched in a tube when the two mechanisms that permit flame propagation—diffusion of species and of heat—are affected. Tube walls extract heat the smaller the tube, the greater is the surface area to volume ratio within the tube and hence the greater is the volumetric heat loss. Similarly, the smaller the tube, the greater the number of collisions of the active radical species that are destroyed. Since the condition and the material composition of the tube wall affect the rate of destruction of the active species [5], a specific analytical determination of the quenching distance is not feasible. 

The rate of destruction of ozone with the oxides of nitrogen relative to the rate in pure air (Chapman model) is defined as the catalytic ratio, which may be expressed either in terms of the variables (N02) and (03) or (NO) and (O). These ratio expressions are... 

He Henry s constant Jf Rate of formation of bubbles per unit volume of solution Jd Rate of destruction of bubbles per unit volume of solution Icl Individual liquid phase mass transfer coefficient Kr Product of gas constant and absolute temperature... 

Complement Some microorganisms produce proteins that bind to and inactivate components of the complement system and hence decrease activation of the cascade, e.g. the vaccinia virus secretes a protein that inhibits activation of both the classical and alternative pathways. Some bacteria produce a protein that mimics the action of an acceleration factor, which increases the rate of destruction of the active convertase this factor is normally produced by the host when the complement response is no longer required. 

Because advanced oxidation processes are based on hydroxyl free-radical chemistry, chemical interactions are highly nonselective. Rates of destruction vary with such factors as the nature of the contaminant mixture, pH, concentration of contaminants, presence of scavengers, and inorganic nature. 

G = —13.6) for electron irradiation in a stream of nitrogen. He attributed the difference in rates of destruction to electron capture by the oxygen impurity in the nitrogen, resulting in longer lifetimes for ionized species and increased yields. 

Initial yields for conversion to the trans-vinylene isomer can be derived by adding to the apparent yield the rate of destruction calculated from the initial concentration of trans-vinylene groups and the first-order rate constants determined for the amorphous trans polymer. The initial yield of trans-vinylene groups is 6.8 for gamma radiation and 4.4 for the reactor. The value for gamma radiation is similar to Golub s value of 7.2 for both gamma and electrons. 

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