Conversion factors, units

To convert from (non-SI unit symbol) to (SI unit symbol) multiply by 

Since a large part of the NEA-TDB project deals with the thermodynamics of aqueous solutions, the units describing the amount of dissolved substance are used very frequently. For convenience, this review uses M as an abbreviation of mol-dm for molarity, c, and, in Appendices B and C, m as an abbreviation of mol-kg for molality, m. It is often necessary to convert concentration data from molarity to molality and vice versa. This conversion is used for the correction and extrapolation of equilibrium data to zero ionic strength by the specific ion interaction theory, which works in molality units (c/ Appendix B). This conversion is made in the following way. Molality is defined as moles of substance B dissolved in 1 kilogram of pure water. Molarity is defined as Cg moles of substance B dissolved in (/ - c M) kilogram of pure water, where p is the density of the solution in kg-dm and the molar weight of the solute in kg-mof.  

When the ionic strength is kept high and constant by an inert electrolyte, I, the ratio OTb /cb can be approximated by  

Baes and Mesmer [76BAE/MES], (p.439) give a table with conversion factors (from molarity to molality) for nine electrolytes and various ionic strengths. Conversion factors at 298.15 K for twenty four electrolytes, calculated using the density equations reported by Sohnel and Novotny [85SOH/NOV], are reported in Table 11-5. 

It should be noted that equilibrium constants need also to be converted if the concentration scale is changed from molarity to molality or vice versa. For a general equilibrium reaction, 0 = SVgB, the equilibrium constants can be expressed either in molarity or molality units, or, respectively  

Most chemical calculations involve calculating one type of quantity, given another, or converting from one unit of measurement to another. For example, in the chemical reaction 

As another example of the use of a unit conversion factor, calculate the number of liters of gasoline required to fill a 12-gallon fuel tank, given that there are 4 gallons in a quart and that a volume of 1 liter is equal to that of 1.057 quarts. This problem can be worked by first converting gallons to quarts, then quarts to liters. The two unit conversion factors required are the following 

Both unit conversion factors are used to calculate the capacity of the tanV in liters  

The preceding examples show that units are canceled in mathematical operations, just as numbers may be. When the same unit appears both above and below the line in a mathematical operation, the units cancel. An example of such an operation is shown for lb in the following, in which the unit of lb simply cancels, leaving kg as the unit remaining  

If the number of Mg is to be calculated given a mass in T, the unit conversion factor needed is 

---

Exact numbers, such as the stoichiometric coefficients in a chemical formula or reaction, and unit conversion factors, have an infinite number of significant figures. A mole of CaCb, for example, contains exactly two moles of chloride and one mole of calcium. In the equality... 

Quantity Customary or commonly used unit SI unit Alternate SI unit Conversion factor multiply customary unit by factor to obtain SI unit ... 

All data are given in U, S, customary units since the charts are in these units. Conversion factors to SI units are given on the charts. 

Converting a measurement from one unit to anotlier can conveniently be accomplished by using unit conversion factors, tliese factors are obtained from tlie simple equation that relates tlie two units numerically. The following is an example of a unit conversion factor... 

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. 

The more permeable component is called the fast gas, so it is the one enriched in the permeate stream. Permeabihly through polymers is the product of solubility and diffusivity. The diffusivity of a gas in a membrane is inversely proportional to its kinetic diameter, a value determined from zeolite cage exclusion data (see Table 20-26 after Breck, Zeolite Molecular Sieves, Wiley New York, 1974, p. 636). Tables 20-27, 20-28, and 20-29 provide units conversion factors useful for calculations related to gas-separation membrane systems. 

Laboratory Conventional Units Conversion Factor SI Units... 

APPENDIX R—SI TO U.S. UNITS CONVERSION FACTORS, SYMBOLS, DEFINITIONS, AND ABBREVIATIONS... 

Dimension measured Metric unit English unit Conversion factor F... 

Instructors can cover as much of the Fundamentals as they wish, whenever they wish skip it all or assign it for independent study. Students can also turn to the Appendixes for help with mathematics, units, conversion factors, and the correct use—within the normal practice of general chemistry, at least—of significant figures. 

---