Conversions, unit metric

In this chapter, I offer suggestions on how to choose the unit or units and then how to work with the unit or units you ve chosen. This chapter also covers the tricky conversions of square feet to square inches or cubic yards to cubic feet. And, of course, no discussion of units is complete without introducing meters and kilograms, so you get conversions involving metric and English measures. 

The international system of units is described in detail in NIST Special Publication 81l,1 and lists of physical constants and conversions factors of selected unit conversions1 5 are given in the following tables. The conversions are presented in matrix format when all of the units are of a convenient order of magnitude. When some of the unit conversions are of tittle value (such as the conversion between metric tons and grains), tabular form is followed, with the less useful units omitted. 

For direct conversions between metric and U.S. customary units, use the following tables. However, if you intend to convert an entire U.S. customary formula using 32 ounces of liquid to a metric formula using 1 liter, or vice versa, use the compound equivalents following these tables. To convert an individual measure, use the direct equivalents. 

In this unit you will find explanations, examples, and practice dealing with the calculations encountered in the chemistry discussed in this book. The types of calculations included here involve conversion factors, metric use, algebraic manipulations, scientific notation, and significant figures. This unit can be used by itself or be incorporated for assistance with individual units. Unless otherwise noted, all answers are rounded to the hundredth place. The calculator used here is a Casio FX-260. Any calculator that has a log (logarithm) key and an exp (exponent) key is sufficient for these chemical calculations. 

In the literature, information is found using different systems of units metric, SI, and the English system. Quotations from the literature are presented in their original form. It would be difficult to change all these units in the book to one system. To assist the reader in converting these units, an appendix is provided with conversion factors for all units found in the text. 

The amounts of utilities consumed are easily estimated from the production rate and the information in the problem statement (with conversion to metric units). 

Key Words Conversion factors, British units, metric units, physical constants, water properties, periodic table of the elements, environmental engineers, Lenox Institute of Water Technology. 

The conversion of a quantity expressed in units of one system to an equivalent quantity in the other system (English to metric or metric to English) requires a bridging conversion unit. Examples are shown in Table 1.3. 

Long the language universally used in science, the SI has become the dominant language of international commerce and trade. The system is nearly universally employed, and most countries do not even maintain official definitions of any other units. A notable exception is the United States, which continues to use customary units in addition to SI. In the United Kingdom, conversion to metric units is government policy, but the transition is not quite complete. Those countries that still recognize non-SI units (e. g., the US and UK) have redefined their traditional non-SI units in SI units. 

English units may need conversion to metric units or vice versa. 

Conversions between metric units are an example of proportional reasoning. Let s examine the 1000-units-per-kilounit relationship more closely. In any measured quantity, the number of units is directly proportional to the number of kilounits ( of units) ( of kUounits). In the form of Equation 3.2, ( of units) = m X ( of kilounits). Solving for the proportionality constant, m, gives... 

So has the conversion to metrics been lost in the United States Not really. Economic motives for the conversion could be stronger than public opposition to change. If by adopting metrics, and paying the one-time costs that go along with it, a company can (a) make more money, (b) save money, or (c) avoid losing money, you can be quite sure that metrics will be adopted. Here are a few examples. 

Units. The SI system of units and conversion factors (qv) has been formally adopted worldwide, with the exception of Bmnei, Burma, Yemen, and the United States. The participation of the United States in the metrication movement is evident by the passage of the Metric Acts of 1866 and 1975 and the subsequent estabUshment of the American National Metric Council (private) and the U.S. Metric Board (pubHc) to plan, coordinate, monitor, and encourage the conversion process. 

Double-Absorption Plants. In the United States, newer sulfuric acid plants ate requited to limit SO2 stack emissions to 2 kg of SO2 per metric ton of 100% acid produced (4 Ib /short ton Ib = pounds mass). This is equivalent to a sulfur dioxide conversion efficiency of 99.7%. Acid plants used as pollution control devices, for example those associated with smelters, have different regulations. This high conversion efficiency is not economically achievable by single absorption plants using available catalysts, but it can be attained in double absorption plants when the catalyst is not seriously degraded. 

For permeation of flavor, aroma, and solvent molecules another metric combination of units is more useful, namely, (kg-m)/(m -sPa). In this unit the permeant quantity has mass units. This is consistent with the common practice of describing these materials. Permeabihty values in these units often carry a cumbersome exponent hence, a modified unit, an MZU (10 ° kgm)/(m -s-Pa), is used herein. The conversion from this permeabihty unit to the preferred unit for small molecules depends on the molecular weight of the permeant. Equation 4 expresses the relationship where MW is the molecular weight of the permeant in daltons (g/mol). 

Estimated imports of calcium chloride increased more than tenfold between 1984 and 1988, from 10,000 to 139,700 metric tons on a 100 wt % basis (10). Import figures (12) do not distinguish between solution or dry calcium chloride or the purity of dry products. Thus estimates of imported quantities involve an assessment of the mix of products imported and ultimate conversion to 100% basis. Imports in 1989 totaled 119,000 metric tons, 75% of which were from Canada (12). Canada is the principal trading partner with the United States for calcium chloride because of use as a deicing chemical and the... 

TABLE 1-5 Metric Conversion Factors as Exact Numerical Multiples of SI Units... 

Applicable dimensional units are shown individuaUy with each equation. The International Metric System (SI) is used when feasible otherwise commonly used U.S. engineering units are employed. The reader is referred to Sec. 1 for unit conversion fac tors. 

TABLE 21-21 Expected Metric Conversion of Packages for Chemical Products in the United States... 

Hard conversion resized package dimensions to told tke nearest acceptable metric unit. Example 50-lL (22.7-kg) miiltiwall paper Lag changed to bold 25 kg (55.1 lb). Size can be limited by tbe maximiim-size package available. 

A minor problem arises in regard to nitrogen oxides. It is common practice to add concentrations of nitrogen dioxide and nitric oxide in ppm (vol) and express the sum as "oxides of nitrogen." In metric units, conversion from ppm (vol) to /rg/m must be done separately for nitrogen dioxide and nitric oxide prior to addition. 

Customary Unit BallPark Metric Values (Do Not Use As Conversion Factors) ... 

Conversions between English and metric units can be made using Table 1.3. 

Conversion of units from one system to another is simply carried out if the quantities are expressed in terms of the fundamental units of mass, length, time, temperature. Typical conversion factors for the British and metric systems are ... 

All units in this book are metric, specifically the International System of Units (SI) and ametric conversion guide is included atthe end of the book. 

Beginning students often regard the metric system as difficult because it is new to them and because they think they must learn all the English-metric conversion factors (Table 2-3). Engineers do have to work in both systems in the United States, but scientists generally do not work in the English system at all. Once you familiarize yourself with the metric system, it is much easier to work with than the English system is. 

Instructors often require English-metric conversions for two purposes to familiarize the student with the relative sizes of the metric units in terms of the more familiar English units, and for practice in conversions (see Sec. 2.4). Once you really get into the general chemistry course, the number of English-metric conversions that you do is very small. 

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