Concentrations conversion between units

TABLE 2.5 Conversion between Units of Concentration in ppm, pphm, ppb, ppt, and Molecules cm 3, Assuming 1 atm Pressure and 25°C ... 

The rate constants for second-order reactions can be expressed in dm mol sec, or, if the rate is measured from the change of gas pressure at constant volume, as described in eq. (2.12), in (pressure) V(time)". The conversion between units of pressure and those of concentration for gas phase reactions which are not first order, can be obtained from the perfect gas equation, from which, for the general case of a reaction of order n, the variation in the total gas pressure can be related to the change in the total gas concentration hy p = cRT... 

Conversions between concentration units are relatively straightforward provided you first decide on a fixed amount of solution. The amount chosen depends on the unit in which concentration is originally expressed. Some suggested starting quantities are listed below. 

As the result of theoretical consideration of polycondensation of an arbitrary mixture of such monomers it was proved [55,56] that the alternation of monomeric units along polymer molecules obey the Markovian statistics. If all initial monomers are symmetric, i.e. they resemble AaScrAa, units Sa(a=l,...,m) will correspond to the transient states of the Markov chain. The probability vap of transition from state Sa to is the ratio Q /v of two quantities Qa/9 and va which represent, respectively, the number of dyads (SaSp) and monads (Sa) per one monomeric unit. Clearly, Qa(S is merely a ratio of the concentration of chemical bonds of the u/i-ih type, formed as a result of the reaction between group Aa and Ap, to the overall concentration of monomeric units. The probability va0 of a transition from the transient state Sa to an absorbing state S0 equals l-pa where pa represents the conversion of groups Aa. 

No deaths or evidence of toxicity were attributable to diisopropyl methylphosphonate administered for 26 weeks in the drinking water of rats at concentrations of 0.6 ppb, 6.0 ppb, 10 ppm, and 1,000 ppm (6.6x 10"7, 6.6x 10"5, 0.011, and 1.1 mg/kg/day, respectively) (Army 1978). It should be noted that there is some confusion concerning the concentration units used in this study (EPA 1989). EPA (1989) states that conversions between ppm and mg/L were incorrectly calculated using the air conversion factor. 

Unfortunately, many of the standard equations encountered in electrochemistry require the concentration unit of mol cm (moles per cubic centimetre). The conversion between mol cm and the familiar mol dm is as follows ... 

The composition of a mixture need not be given in terms of the mole fractions of its components. Other scales of concentration are frequently used, in particular, when one of the components, say. A, can be designated as the solvent and the other (or others), B, (C,...) as the solute (or solutes). When the solute is an electrolyte capable of dissociation into ions (but not only for such cases), the molal scale is often employed. Here, the composition is stated in terms of the number of moles of the solute, m, per unit mass (1 kg) of the solvent. The symbol m is used to represent the molal scale (e.g., 5 m = 5 mol solute/1 kg solvent). The conversion between the molal and the rational scale (i.e., the mole fraction scale, which is related to ratios of numbers of moles [see Eq. (2.2)] proceeds according to Eqs. (2.32a) or (2.32b) (cf. Fig. 2.4) ... 

The osmolahty of a contrast agent solution is proportional to the number of independent particles in the solution and is strongly influenced by both the concentration of the contrast agent (or any other constituents) and the temperature of the solution. The osmotic pressure of a contrast agent preparation is given in milliosmol kg water (mosm kg ), in Megapascal (MPa) or in atmospheres (at). Conversion between the different units follows the equation 1 osm kg = 1000 mosm kg = 2.58 MPa = 25.5 at. In a multi-component system, the osmolality is defined as... 

The conversion between concentration units and the expression of the units themselves can be confusing. We will now review the typical concentration units used in various environmental media. Concentration in water is usually given as mass per unit volume or moles per unit volume. The conversion between them is a straightforward application of molecular weights. For example, we have 2.0 g/m of CO2 dissolved in water. The molecular weight of carbon dioxide is 44 g/mole. Then the concentration in moles/m is... 

It is important to be able to convert among the different concentration units. Conversions between molality and mole fraction are performed by considering a solution containing 1 kg of solvent ... 

The reverse rate constants for the elementary reactions used in the present work were caJculated from the forward rate constants and the equilibrium constant by assuming microscopic reversibility. Standard states used in tabulations of thermodynamic data are invariably at 1 atm and the temperature of the system. Since concentration units were required for rate constant calculations, a conversion between Kp and Kc was necessary. Values of Kp were taken from the JANAF Thermochemical tables (1984). Kc was calculated from the expression ... 

Practically, chemical concentrations are reported in different units. For the conversion between the most common units and the GF3 code units, a list of conversion factors is given in Table 20.5, based on most recent reference data(lUPAC, 2005 ICES, 2006 IOC, 2006). 

Problem 8.5 Consider the flow tube for rapid polymerization reactions shown schematically in Fig. 8.1. Let V be the volume of the tube (distance between the mixing jets) and V be the volume of the total liquid flowing through in time t. Denoting the total concentration (constant) of polymer chain ends by Eq. (8.29) and the concentration of monomer units in polymer by [Mjp derive an expression for monomer conversion as a function of t. 

For aqueous-phase chemical reactions the commonly used concentration unit is mol L 1. Aqueous solutions in cloud and raindrops are characterized by concentrations in the range of pmolL. For a dilute aqueous solution molality (mol kg-1) is approximately equal to molarity (mol L-1). The conversion between molar concentration c and molality m is... 

To convert between units of radon-222 radioactivity (Ci or Bq) and the potential alpha energy concentration (WL or J/m the equilibrium between radon gas and radon daughters must be known (See Chapter 9 for conversion formula). When radon is in equilibrium with its progeny, that is, when each of the short-lived radon daughters is present at the same activity concentration in air as radon-222, then 1 WL equals 100 pCi radon-222/L of air. However, when removal processes other than radioactive decay are operative, such as with ventilation, the concentration of short- lived daughters will be less than the equilibrium amount. In such cases an equilibrium factor (F) is applied. For example, if the equilibrium factor is 0.5, then 200 pCi radon-222/L of air is equivalent to 1.0 WL if the equilibrium factor is 0.3, then 1 WL corresponds to 333 pCi radon-222/L of air. 

The difficulty results, in part, from the fact that only a small fraction of the chemical bonds, generally less than one in a thousand, are involved in me-chanochemical processes. The concentration of connecting units is therefore at the detection limit and below for traditional analytical methods such as conventional nuclear magnetic resonance and infrared spectroscopy. The sensitivity can, of course, be enhanced by techniques such as cumulative, multiple scans, Fourier transform analysis, and difference techniques for detection to one part in ten thousand and better. It may yet be difficult to determine whether polymers are linked by chemical bonds or whether they are simply intimate mixtures. For this distinction, other tests can be of value. For example, the difference between blocks and blends for ethylene-propylene polymer systems has been distinguished by thermal analysis [5]. In many cases, simple extraction tests can distinguish between copolymers and blends. For example, for rubber milled into polystyrene, the fraction of extractable rubber is a measure of mechanochemistry. Conversely, only the rubber in this system is readily cross-linked by benzoyl peroxide after which free polystyrene may be conveniently extracted [6]. In another case, homopolymers of styrene and methyl methacrylate can be separated cleanly from each other and from their copolymers by fractional precipitation [7]. The success of such processes, of course, depends on both the compositions and molecular weights involved. 

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