8_Standard%20State

8_Standard%20State - Standard States Most state variables...

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1 Most state variables cannot be measured absolutely. One can only determine their relative values. V/V ref , T, P, H, U, S, etc. Examples: L = ( L/L ref )L ref => calculate V T = T + T ref S = S + S ref To determine the values of T, P, H, etc., we need to know a reference value or a standard. As a result, Standard States 1. Weight and height. Reference Values of Physical Quantitities The standard kilogram housed at the International Bureau of Weights and Standards near Paris. 90% platinum and 10% iridium. US National meter #27, a copy of international meter made of platinum and iridium in France. It is housed at the National Institute of Standard and Technology Museum. 2. Pressure - Room pressure: in the clinic - Vacuum pressure: in thermodynamics 3. Temperature - Temperature of triple point of water at P = 1 atm (for 0 C) - Temperature of gases as V 0 at any P (for K)
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2 Based on Boltzmann Equation in stat mech, S of any chemically homogeneous solid or liquid = 0 at T = 0 K (the Third Law of Thermodynamics.) Note: • There is only one microstate for pure crystal at 0 K. In a mixture , there are a finite number of microstates at 0 K. Thus, S 0. • The crystal can be made of either element or compound . 4. Entropy of homogeneous substance - Entropy as T 0 K 5. H and G as well as S of ions - None => One cannot determine the absolute values of H and G for any elements or compounds. => Using H, G, and S of other elements or ions as references. Ions S 0 ref = S 0 (H + ,aq) f G 0 ref = f G 0 (H + ,aq) f H 0 ref = f H 0 (H + ,aq) Pure Elements or Compounds elements) (stable H H j j ref 0 0 ements) (stable el G j j 0 ref 0 G e.g., C + O 2 CO 2 ) O ( H ) graphite ( H ) CO ( H ref 0 2 2 => One cannot determine the absolute values of H, G and S for any ions (since it cannot be purified).
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This note was uploaded on 01/17/2010 for the course BME 100 taught by Professor Yuan during the Fall '07 term at Duke.

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8_Standard%20State - Standard States Most state variables...

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