Non SI units

API American Petroleum Institute gravity Bpcd barrels per calendar day 

1 Rana MS, Samano V, Ancheyta J, Diaz JAI. A review of recent advances on process technologies for upgrading heavy oils and residua. Fuel 2007 8 1216-1231. 

2 Furimsky E. Selection of catalysts and reactors for hydroprocessing. Appl. Catal. A Gen. 1998 171 177-206. 

4 Mederos FS, Elizalde 1, Ancheyta J. Steady-state and dynamic reactor models for hydrotreatment of fractions A review. Catal. Rev. Sci. Eng. 2009 51 485-607. 

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We will quote a numerical constant in some of these equations to help with actual calculations. The units can be very confusing because it is conventional to use non-SI units for several quantities. The wavenumber value, i>, is usually taken to be in cm The extinction coefficient is conveniently taken in units of 1 moH ... 

Table 2.2 provides a list of other important derived SI units, as well as a few commonly used non-SI units. 

Pressure is defined as force per unit of area. The International System of Units (SI) pressure unit is the pascal (Pa), defined as 1.0 N /m. Conversion factors from non-SI units to pascal are given in Table 1 (see also Units and conversion factors front matter). An asterisk after the sixth decimal place indicates that the conversion factor is exact and all subsequent digits are 2ero. Relationships that are not followed by an asterisk are either the results of physical measurements or are only approximate. The factors are written as numbers greater than 1 and less than 10, with 6 or fewer decimal places (1). 

Units Used with SI. A number of non-SI units are used in SI (Table 2). 

Units Used Temporarily with SI. Additional non-SI units are used with SI units until the CIPM considers their use no longer necessary (Table 3). 

The former (non-SI) unit of dose equivalent was the roentgen equivalent man (rem), which was defined in the same way as the sievert but with the absorbed dose in rad thus, 1 rem = 10 2 Sv. 

A unit equality may link SI units and non-SI units (1 quart = 0.946353 L), decimally related units (10 c = 1 m ), or base units and derived units (1 L = 10 m ). Some of the more common unit equalities are given on the inside back cover of this text. Examples and treat unit conversions. 

The use of non-SI units is strongly discouraged. For these units there often do not exist standards, and for historical reasons the same denomination may mean sundry units. For example, it is common practice in theoretical chemistry to state energy values in kilocalories. However, to convert a calorie to the SI unit Joule, there exist different conversion factors ... 

Some non-SI units are explicitly permitted. They include for crystallographic statements 1 A = 1CT10 m = 100 pm and 1° = tt/ 180 rad (plane angle). The liter is also permitted (both abbreviations are official, L or 1) 1 L = 1 dm3. 

Tables C. 1-C.4 provide conversion factors from a.u. to SI units and a variety of practical (thermochemical, crystallographic, spectroscopic) non-SI units in common usage. Numerical values are quoted to six-digit precision (though many are known to higher accuracy) in an abbreviated exponential notation, whereby 6.022 14(23) means 6.022 14 x 1023. In this book we follow a current tendency of the quantum chemical literature by expressing relative energies in thermochemical units (kcal mol-1), structural parameters in crystallographic Angstrom units (A), vibrational frequencies in common spectroscopic units (cm-1), and so forth. These choices, although inconsistent according to SI orthodoxy, seem better able to serve effective communication between theoreticians and experimentalists.

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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