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TAMU CHEM 101 - Chap1x-103
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-1.1-Facts 6 Laws 6 Theories(experimental (summary statements (simplified understanding Observations) of facts - prediction of of nature - tells how & why) what will happen)CHAPTER 1. FUNDAMENTAL CONCEPTS OF CHEMISTRYA. IntroductionChemistry is the area of science concerned with the properties of atoms and aggregates ofatoms called molecules. The goals of chemical investigation are to develop a fundamentalunderstanding of phenomena relating to the formation, properties, interactions and transformationsof molecules, and to utilize this knowledge for the good of humankind. In general, scientificinvestigation follows a logical sequence of steps called the “scientific method”. The scientificmethod consists of (a) characterizing the phenomenon of interest by making definitive experimentalobservations, (b) deducing laws which summarize a body of experimental facts and enable theprediction of what will happen when variables are changed, and (c) formulating theories which relatethe observed behavior to the fundamental nature of matter. In this introductory course in chemistry, our main objectives will be to develop a languageappropriate for the quantitative and qualitative study of the properties of atoms and molecules, andto cultivate an ability to formulate and solve problems utilizing the language and methods ofchemistry. As an illustration of the magnitude of the task at hand, consider a familiar chemicalprocess - the combustion of a piece of paper. Suppose we wish to arrive at a detailed understandingof this process. How should we proceed? As a start, we could make qualitative observations toestablish the general characteristics of the phenomenon: light is produced, heat is evolved, gases aregenerated. We must next perform quantitative measurements (how much light, what are thewavelengths, how much heat, what kinds of gases, how much of each gas, etc.) and then utilize whatis known about the origin of light (quantum theory and spectroscopy), the generation of heat(thermodynamics), the conversion of one substance into another (chemical reactions, stoichiometry-1.2-and kinetics) to achieve our objective of “understanding” what is happening when a piece of paperburns.All scientific languages require precise definitions of the properties to be investigated andquantitative scales and units by which they can be measured. Therefore, as the first topics ofdiscussion, we shall embark on a brief review of common units of measurement and conversionfactors.B. Units of MeasurementExperimental observation requires measurement. To make a measurement one needs:1. A precise definition of the property to be measured (i.e., length = straight-line distancebetween two points).2. A measurement standard (e.g., Pt-Ir bar at the National Bureau of Standards).3. A measurement device or instrument (a ruler or meter stick that has been calibrated againstthe standard).A wide variety of units are in common usage throughout the world. In the USA, wecommonly use the English system of units for the various basic quantities listed in the table below.Quantity Definition Common Units Mass Quantity of matter kg, g, oz, lb, ton Length Distance between two points km, m, cm, in, yd, ft, mi Time Interval between two events s, min, hr, yr Temperature Heat intensity (kinetic energy) K, C, F, R0 0 0 0In scientific endeavors, however, it is customary to use the metric system of units. Two sets of metricunits are in common usage; the cgs (centimeter, gram, second) system and the mks (meter, kilogram,second) system. In an effort to standardize units, a system of international units (SystemeInternationale or SI) has been agreed upon. The mks units were chosen as the SI units for distance,mass and time. Nevertheless, other units are still commonly used in special instances because of theconvenience they offer. For example, when dealing with atomic dimensions, it is generally moreconvenient to express lengths in terms of Angstroms than meters.dvdtd2xdt2dxdt2-1.3-Once a set of units has been chosen for the fundamental quantities discussed above, units forother quantities may be derived from their functional dependence on the fundamental quantities.Examples of common derived units are given in the following table.Derived UnitsVolume (Length) m , cm , L (1 L=1000 cm )3 3 3 3Force F = ma = m kg m/s = N (Newton)2 = m g cm/s = dyne2Energy E = ½mv kg (m/s) = J (Joule)2 2 = ½m g (cm/s) = erg2Pressure P = F/A N/m = Pa (Pascal) (1 atm = 101.3 k Pa =2 14.7 psi; 1 bar = 100 k Pa)C. Conversion FactorsBecause we will be employing a variety of units in this course, it will be necessary for youto be able to easily convert from one to another. This can be accomplished by using conversionfactors. A conversion factor is an equality in the sense that it relates two equal quantities. Examplesof common conversion factors with which you should already be familiar arel ft = l2 in l yd = 3 ft 1 mi = 5280 ftl lb = l6 oz l ton = 2000 lb 1 hr = 3600 s.Three very important conversion factors relating length, mass, and volume between the metric andEnglish systems of units are1 in = 2.54 cm 1 lb = 454 g 1 qt = 0.946 LSince both quantities that make up a conversion factor (including units) are equal, their ratio must12 in1 ft' 1 (but121… 1)12 xy' 13 ft x12 in1 ft' 36 in36x1015in. x1 ft12 in.x1 mile5280 ft'(36x1015)(12)(5280)mile ' 5.7x1012mile-1.4-be unity;.The units are treated as algebraic quantities, the same as x and y in the equation 12 x = y.Since a conversion factor (such as the ratio 12 in/1 ft) is unity, multiplication by another quantitydoes not change the absolute magnitude of that quantity - only its units..Both 3 ft and 36 in are expressions of the same length, only in different units!The procedure for unit conversion is simple:1. Start with the quantity you want to convert.2. Multiply it by an appropriate conversion factor arranged such that the old unit cancelsalgebraically and the new unit remains.Examples: a). Convert 36x10 in. to miles.15 .b). Convert 1 kilometer to miles.1 km x1000 m1 kmx100 cm1 mx1 in.2.54 cmx1 ft12 in.x1 mi5280 ft'(1000)(100)(2.54)(12)(5280)mi ' 0.62mi.2 lb iron x454 g iron1 lb ironx1 cm3iron7.86 g ironx1 L iron1000 cm3iron' 0.116 L iron.-1.5-c). Density (ρ = mass/volume) may be regarded as a conversion factor that relates themass of a substance to its volume. What volume in liters is occupied


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TAMU CHEM 101 - Chap1x-103

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