Scientific calculations units

Temperature. The kelvin is the SI unit of thermodynamic temperature, and is generally used in scientific calculations. Wide use is made of the degree Celsius (°C) for both temperature and temperature interval. The temperature interval 1°C equals 1 K exacdy. Celsius temperature, t, is related to thermodynamic temperature, T, by the following equation ... 

Chemistry is full of calculations. Our basic goal is to help you develop the knowledge and strategies you need to solve these problems. In this chapter, you will review the Metric system and basic problem solving techniques, such as the Unit Conversion Method. Your textbook or instructor may call this problem solving method by a different name, such as the Factor-Label Method and Dimensional Analysis. Check with your instructor or textbook as to for which SI (Metric) prefixes and SI-English relationships will you be responsible. Finally, be familiar with the operation of your calculator. (A scientific calculator will be the best for chemistry purposes.) Be sure that you can correctly enter a number in scientific notation. It would also help if you set your calculator to display in scientific notation. Refer to your calculator s manual for information about your specific brand and model. Chemistry is not a spectator sport, so you will need to Practice, Practice, Practice. 

E-mail Address info refiningonline.com Web Address www.refiningonline.com The Refining Connection, a service of Astron International, Inc., is an online refining resource that provides unite conversion tools, information on steam properties, line pressure drop calculators, Internet bulletins, a scientific calculator and various other software. 

Quantitative calculations and qualitative interpretations are fundamental to fully grasp the concepts of chemistry. Quantitative values must include a number and a unit. Two common units of measurement are the conventional (English) system and the metric system. The conventional set of units includes inches, feet, miles, gallons, and pounds. These units, although common in the United States, are not used in science or by most of the world. However, the metric system is becoming more common in the United States. The metric system s base-10 units are easier to use and essential for scientific calculations. However, because most readers of this book are more familiar with the conventional system, it will be necessary to convert to and from the metric system. 

This book is designed to help you leam the fundamentals of chemistry. To be successful, you must master the concepts of chemistry and acquire the mathematical skills necessary to solve problems in this quantitative science. If your algebra is rusty, you should polish it up. Appendix 1 reviews the algebra used in basic chemistry and also shows how to avoid mistakes while solving chemistry problems with your scientific calculator. The factor label method is introduced in Chapter 2 to show you how to use units to help with problem solutions. You can help yourself by using the standard symbols and abbreviations for various quantities (such as m for mass, m for meter, mol for moles, and M for molarity). Always use the proper units with your numerical answers it makes a big difference whether your roommate s pet is 6 inches long or 6 feet long ... 

To use exponential notation to work with very large and very small numbers To use the basic elements of the metric system—a system of units and prefixes designed to make scientific calculations as easy as possible... 

An extremely useful tool for scientific calculations (for everyday calculations too) is dimensional analysis, also called the factor label method. This system enables us to convert from a quantity in one set of units to the same quantity in another set, or from a quantity of one thing to an equivalent quantity of another. For example, if we have 2.00 or 200 cents, we have the same amount of money. We can change from one of these to the other with a factor—a ratio—of 100 cents divided by 1.00 dollar, or the reciprocal of that ratio. 

It would be good to review the section Scientific Calculations (Section 1.1) before attempting this chapter. Pay careful attention to the units. In solving elementary gas law equations, the units of volume and of pressure must be the same every place they appear in each equation the units of temperature not only must be the same, but must be kelvinsl... 

Significant Figures and Calculators When you use a scientific calculator to work problems in scientific notation, don t forget to express the value on the display to the correct number of significant figures and show the units when you write the final answer. 

It is usually the best practice to work through design calculations in the units in which the result is to be presented but, if working in SI units is preferred, data can be converted to SI units, the calculation made, and the result converted to whatever units are required. Conversion factors to the SI system from most of the scientific and engineering units used in chemical engineering design are given in Appendix D. 

It should be noted that a dimensional analysis of this problem results in one more dimensionless group than for the Newtonian fluid, because there is one more fluid rheological property (e.g., m and n for the power law fluid, versus fi for the Newtonian fluid). However, the parameter n is itself dimensionless and thus constitutes the additional dimensionless group, even though it is integrated into the Reynolds number as it has been defined. Note also that because n is an empirical parameter and can take on any value, the units in expressions for power law fluids can be complex. Thus, the calculations are simplified if a scientific system of dimensional units is used (e.g., SI or cgs), which avoids the necessity of introducing the conversion factor gc. In fact, the evaluation of most dimensionless groups is usually simplified by the use of such units. 

When working with measurements, you often have to convert units before performing other calculations. There are two methods of converting measurements. One is using proportions and the other is using a scientific method called dimensional analysis. 

The following examples are presented for individual unit operations found within a fuel cell system. Unit operations are the individual building blocks found within a complex chemical system. By analyzing example problems for the unit operation, one can learn about the underlying scientific principles and engineering calculation methods that can be applied to various systems. This approach will provide the reader with a better understanding of these fuel cell power system building blocks as well as the interactions between the unit operations. For example, the desired power output from the fuel cell unit operation will determine the fuel flow requirement of the fuel processor. 

For the actual values and a discussion on various approaches by a range of scientific groups to calculating such values of unit risks for cancer for the PAHs and PACs in Tables 10.14 and 10.15, see Nielsen et al. (1995, 1996, 1999b), OEHHA/Cal EPA (1998), Collins et al. (1998), and references therein. 

As we have seen in some of the examples described above, an added complication in performing chemical calculations often involves the presence of units. More often than not, these numbers may be expressed in scientific form, and so, in order to rationalize and simplify their specification, it is conventional to use the names and abbreviations given in Table l. 2, adjusting the decimal number given as prefix as appropriate. 

Many scientific activities involve numerical calculations—measuring, weighing, preparing solutions, and so forth—and it s often necessary to convert a quantity from one unit to another. Converting between units isn t difficult we all do it every day. If you run 7.5 laps around a 200 meter track, for instance, you have to convert between the distance unit lap and the distance unit meter to find that you have run 1500 m (7.5 laps times 200 meters/lap). Converting from one scientific unit to another is just as easy. 

Dimensional calculations are greatly simplified if a consistent set of units is employed. The three major reference dimensions for mechanics are length, mass, and time, but length can be measured in units of inches, feet, centimeters, meters, etc. Which should be used The scientific community has made considerable progress toward a common system of reference units. This system is known as SI from the French name Systeme International d Unites. In SI, the reference units for length, mass, and time are the meter, kilogram, and second, with symbols m, kg, and s, respectively. 

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. 

Temperature is the measure of thermal energy (the total energy of all the atoms and molecules) of a system. The SI unit for temperature is Kelvin, but most scientific thermometers use the centigrade (Celsius) scale. However, most are more familiar with the Fahrenheit scale. Because many chemical calculations require Kelvin temperature, scientists frequently convert from degrees Celsius to Kelvin and from Kelvin to degrees Celsius. 

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