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Essay4 - [Type text[Type text ME5446 ESSAY 4 The four...

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[Type text] [Type text] September 23, 2008 ME5446 ESSAY 4 The four elements that are the building blocks for combustion are: oxygen, nitrogen, carbon, and hydrogen. Since the Lords of Combustion have willed that chemical formations will occur at 25C and 1 atmosphere, we note that the stable forms of these elements are: O 2 , N 2 , H 2 , and C. These Lords have specified that the enthalpies of these stable forms are zero at 25C and 1 atmosphere. Suppose that we need the enthalpy of molecular oxygen at some other temperature. To obtain that value, we could go to a thermodynamic table in which that information is given as a function temperature. In that table, the enthalpy of molecular oxygen is set equal to zero at a temperature of 0K. That selection of a datum is intuitively satisfying because all atomic, molecular, and electronic motion ceases at absolute zero. However, the datum of that thermodynamic table is different from the datum selected by the Lords of Combustion for molecular oxygen. That datum, as noted in the preceding paragraph, is 25C and 1 atmosphere.
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