Moles in Thermodynamics

3 Key excerpts on "Moles in Thermodynamics"

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  Commonly Asked Questions in Thermodynamics

  • Marc J. Assael, William A. Wakeham, Anthony R. H. Goodwin, Stefan Will, Michael Stamatoudis(Authors)
  • 2011(Publication Date)
  • CRC Press

    (Publisher)

  One proposed definition for the mole is The mole is the amount of substance of a system that contains exactly 6.022 141 5 ⋅ 10 23 specified elementary entities, which may be atoms, mol-ecules, ions, electrons, other particles or specified groups of such particles. (Mills et al . 2006) 1.3 What Vocabulary Is Needed to Understand Thermodynamics? 9 We digress briefly here to consider, in the same context, the definition of the kilogram, which is currently as follows: The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram sanctioned by the 1st General Conference on Weights and Measures in 1889. One proposed definition for the kilogram that removes the requirement for an arbitrary artifact whose mass is known to drift is The kilogram is the mass of a body whose equivalent energy is equal to that of a number of photons whose frequencies sum to exactly [(299 792 458) 2 / 662 606 93] ⋅ 10 41 hertz. (Mills et al. 2006) With similar redefinitions of the ampere and the Kelvin it would be possible to define six of the seven base units of the SI system in terms of true invari-ants of nature, fundamental physical constants. The current weakness of the definitions of the ampere, the mole, and the candela is derived in large measure from their dependence on the definition of the kilogram and its representa-tional artifact. 1.3.12 What Are Molar and Mass or Specific Quantities? The molar volume of a phase is the quotient of the volume and the total amount of substance of the phase. Generally, any extensive quantity X divided by the total amount of substance Σ B n B is, by definition, an intensive quantity called the molar quantity X m : m B B . X X n = ∑ (1.4) In Equation 1.4 , the subscript m designates a molar quantity and can be replaced by the chemical symbol for the substance in this example, subscript B; when no ambiguity can result the subscripts m and B may be omitted entirely.

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  Engineering and Chemical Thermodynamics

  • Milo D. Koretsky(Author)
  • 2012(Publication Date)
  • Wiley

    (Publisher)

  Strictly speaking, the word molecule is outside the realm of classical thermodynamics. In fact, all of the concepts developed in this text can be developed based entirely on observations of macroscopic phenomena. This development does not require any knowledge of the molecular nature of the world in which we live. However, we are chemical engineers and can take advantage of our chemical intuition. Molecular concepts do account qualitatively for trends in data as well as magnitudes. Thus, they provide a means of understanding many of the phenomena encountered in classical thermodynamics. Consequently, we will often refer to molecular chemistry to explain thermodynamic phenomena. 4 The objective is to provide an intuitive framework for the concepts about which we are learning. 3 Some fields of science such as statistical mechanics use the term microscopic for what we call molecular. 4 While this objective can often be achieved formally and quantitatively through statistical mechanics and quantum mechanics, we will opt for a more qualitative and descriptive approach reminiscent of the chemistry classes you have taken. Units By this time, you are probably experienced in working with units. Most science and engi- neering texts have a section in the first chapter on this topic. In this text, we will mainly use the Système International, or SI units. The SI unit system uses the primary dimen- sions m, s, kg, mol, and K. Details of different unit systems can be found in Appendix D. One of the easiest ways to tell that an equation is wrong is that the units on one side do not match the units on the other side. Probably the most common errors in solving problems result from dimensional inconsistencies. The upshot is: Pay close attention to units! Try not to write a number down without the associated units. You should be able to convert between unit systems. It is often easiest to put all variables into the same unit system before solving a problem.

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  Chemistry

  Structure and Dynamics

  • James N. Spencer, George M. Bodner, Lyman H. Rickard(Authors)
  • 2011(Publication Date)
  • Wiley

    (Publisher)

  31 Chapter Two THE MOLE: THE LINK BETWEEN THE MACROSCOPIC AND THE ATOMIC WORLDS OF CHEMISTRY 2.1 The Mole as the Bridge between the Macroscopic and Atomic Scales 2.2 The Mole as a Collection of Atoms 2.3 Converting Grams into Moles and Number of Atoms 2.4 The Mole as a Collection of Molecules 2.5 Percent by Mass 2.6 Determining the Formula of a Compound 2.7 Two Views of Chemical Equations: Molecules versus Moles 2.8 Mole Ratios and Chemical Equations 2.9 Stoichiometry 2.10 The Stoichiometry of the Breathalyzer 2.11 The Nuts and Bolts of Limiting Reagents 2.12 Density 2.13 Solute, Solvent, and Solution 2.14 Concentration 2.15 Molarity as a Way to Count Particles in a Solution 2.16 Dilution Calculations 2.17 Solution Stoichiometry 2.1 The Mole as the Bridge between the Macroscopic and Atomic Scales Imagine that you pick the following items off the shelves of a grocery store: a dozen eggs, a 1-lb bag of sugar, a 5-lb bag of flour, and a quart of milk. When you open the egg carton, you know exactly how many eggs it should contain––a dozen. But the same can’t be said about either the sugar, the flour, or the milk. A recipe may call for 1 egg, but it never calls for 1 grain of sugar because a grain of sugar is too small to be useful. Recipes therefore tend to call for half a cup of sugar or two cups of flour or a cup of milk. Chemists face a similar problem because it takes an enormous number of atoms to give a sample large enough to be seen with the naked eye. (A dot of graphite from a pencil just large enough to be weighed on an analytical balance contains approximately 5  10 19 atoms.) Chemists therefore created a unit known as the mole (from Latin, meaning “a huge pile”) that can serve as the bridge between chemistry on the macroscopic and atomic scales. A mole is the amount of substance that contains as many elementary units as there are atoms in exactly 12 grams of the carbon-12 isotope.

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