S k lnW 0 Entropy is absolute not relative like energy Kelvin temperature is a

# S k lnw 0 entropy is absolute not relative like

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S = k ln(W) = 0 Entropy is absolute, not relative like energy. Kelvin temperature is a measure of accessible states and available energy. 4 7 Standard Molar Entropy Unlike energy, there is an absolute 0 for entropy. T = 0 K then S system = 0. Since entropy is absolute, entropy values can be tabulated for any system and any conditions. The standard molar entropy is a measure of the number of states over which energy has been dispersed in going from the perfect crystal at 0 K to the situation at 298 K, 1 atm pressure, and 1 M concentrations. Values in text p. 648 and Appendix 4. 8 Calculation of Standard Entropy Changes from Standard Molar Entropy Values S o reaction = S o products S o reactants Calculate the standard entropy change for the following reaction. 2H 2 (g) + O 2 (g) 2H 2 O(g) 190 H 2 O 205 O 2 130 H 2 S o J K –1 mol –1 Is +58 J/K the correct answer? A)Yes B)No C)Haven’t a clue! 5 Calculation of Standard Entropy Changes from Standard Molar Entropy Values S o reaction = S o products S o reactants Calculate the standard entropy change for the following reaction. 2H 2 (g) + O 2 (g) 2H 2 O(g) 190 H 2 O 205 O 2 130 H 2 S o J K –1 mol –1 S o = 2(190) – 205 – 2(130) = – 85 J/K The – sign means the entropy decreased as a result of the reaction. The energy is spread out over the states of 2 molecules in the products and over the states of 3 in the reactants. The energy is less dispersed in the products so the entropy decreased. 10 Entropy S, Energy Flow q, & Temperature T S = k ln(W) If energy, q, is added to or removed from a system, the number of accessible microstates changes.  #### You've reached the end of your free preview.

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• Spring '08
• LaceyandHanson
• Entropy, Law of Thermodynamics, standard molar entropy
• • •  