Some Unit Conversion Factors

Integers and exact numbers In multiplication or division by an integer or an exact number, the uncertainty of the result is determined by the measured value. Some unit conversion factors are defined exactly, even though they are not whole numbers. For example, 1 in. is defined as exactly 2.54 cm and the 273.15 in the conversion between Celsius and Kelvin temperatures is exact so 100.000°C converts into 373.150 K. 

Table 1.9. Examples of Some Unit Conversion Factors...

Table 1.9 gives some unit conversion factors calculated from the information given in Tables 1.6-1.8 and in preceding parts of this chapter. Note that, in each case, two unit conversion factors are calculated the one that is used depends upon the units that are required for the answer. 

Some approximate conversion factors to SI units are given in Table 1.1. These are worth committing to memory, to give some feel for the units for those more familiar with the traditional engineering units. The exact conversion factors are also shown in the table. A more comprehensive table of conversion factors is given in Appendix D. 

The International Units, some useful Conversion Factors, and numerical Constants... 

A conversion factor simply uses your knowledge of the relationships between units to convert from one unit to another. For example, if you know that there are 2.54 centimeters in every inch (or 2.2 pounds in every kilogram or 101.3 kilopascals in every atmosphere), then converting between those units becomes simple algebra. Peruse Table 2-3 for some useful conversion factors. And remember If you know the relationship between any two units, you can build your own conversion factor to move between those units. 

Defined values for example, unit conversion factors, mathematical constants, or the values of constants used to relate some SI units to fundamental constants. 

Some numerical values are exact to as many significant figures as necessary, by definition. Included in this category are the numerical equivalents of prefixes used in unit definition. For example, 1 cm = 0.01 m by definition, and the units conversion factor, 1.0 x 10-2 m/cm, is exact to an infinite number of significant figures. 

Presented in this appendix are a list of basic and derived SI units, some fundamental constants frequently required by inorganic chemists, and some useful conversion factors. 

Absolute integrated intensities given in all tables are in practical units 109, 125), whereas it must be noted that A as defined in the text [Eq. (8)] is the Ramsay and Jones unit. Conversion factors interrelating some of the various commonly used units of intensity to practical units are to be found in Table VIII. 

APPENDIX 1.1 SOME USEFUL QUANTITIES, UNITS, CONVERSION FACTORS, CONSTANTS, AND RELATIONSHIPS... 

Thermodynamic data are given according to the Systeme International d unites (SI units). The unit of energy is the joule. Some basic conversion factors, also for non-thermodynamic units, are given in Table II-4. 

The use of these various units is rational, but confusing. As in other areas of science, historical units often stay in use for a long time even after SI units have been officially adopted. Table 5.3.8.4 shows the various units of measurement for radiation and some useful conversion factors. 

Despite the fact that for the most part onl)t SI units are used in this book (see polic) on units), it is important to note some exact conversion factors between SI and CGS units since the remanence of obsolete CGS electromagnetic units are still important in the technical literature on magnetism, especiall) when examining data contained in old treatises or technical specifications. 

The SI system of units is the internationally accepted form of the metric system. The SI system is being used increasingly in chemistry, as in other sciences, but some older units persist. This book reflects this dichotomy, although the SI system has been used as much as possible. Some useful conversion factors between various units are given in Appendix II. 

Some useful conversion factors involving energy and mass units are summarized in Table 1.2 for a more detailed listing of fundamental constants and conversion factors see Appendix (Tables A.l and A.2). 

In some cases conversion factors had to be used to give the tabulated parameters in the quoted units. These factors have been calculated with the fundamental constants given in 1. But the accuracy of the measured magnetic constants is not sufficient to differentiate between earlier used fundamental constants. 

Most theoretical results are obtained in atomic units (a.u.), whereas experimental data often are given in SI or esu units. In O Table 11-1 some useful conversion factors are given. 

The system of atomic units was developed to simplify mathematical equations by setting many fundamental constants equal to 1. This is a means for theorists to save on pencil lead and thus possible errors. It also reduces the amount of computer time necessary to perform chemical computations, which can be considerable. The third advantage is that any changes in the measured values of physical constants do not affect the theoretical results. Some theorists work entirely in atomic units, but many researchers convert the theoretical results into more familiar unit systems. Table 2.1 gives some conversion factors for atomic units. 

Designers, manufacturers, and operators of boilers continue to use many of these terms, without undue deference to unit standardization, to define, measure, and report on plant steam-raising capacities power output) and operating parameters. (In continuance of this common practice therefore, many of these various terms are freely used in discussions throughout this book.) However, to familiarize the reader and minimize confusion, some energy terms and notes are provided here. A more complete list of units and conversion factors is provided in the appendix. 

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. 

Where, for convenience, other than SI units have been used on figures or diagrams, the scales are also given in SI units, or the appropriate conversion factors are given in the text. The answers to some examples are given in British engineering units as well as SI, to help illustrate the significance of the values. 

Table 1.3 gives some commonly used non-SI units for certain quantities, together with conversion factors relating them to SI units. We use these in some examples and problems, except for the calorie unit of energy. This last, however, is frequently encountered. 

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