Lec06_drobny_11 - Lecture 6: Standard Enthalpies •...

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Unformatted text preview: Lecture 6: Standard Enthalpies • Reading: Zumdahl 9.6 • Recommended Problems:9.61, 9.63, 9.67, 9.69 • Outline – What is a standard enthalpy? – Defning standard states. – Using standard enthalpies to determine Δ H° rxn Defnition oF Δ H° F • We saw in the previous lecture the utility oF having a series oF reactions with known enthalpies. •What iF one could deal with combinations oF compounds directly rather than dealing with whole reactions to determine Δ H rxn ? Defnition oF Δ H° F (cont.) • Standard Enthalpy oF ¡ormation, Δ H° F : “The change in enthalpy that accompanies the Formation oF 1 mole oF a compound From its elements with all substances at standard state .” • We envision taking elements at their standard state, and combining them to make compounds, also at standard state. What is Standard State? • Standard State: A precisely defned reFerence state. It is a common reFerence point that one can use to compare thermodynamic properties. • Defnitions oF Standard State: – ¡or a gas: P = 1 atm. – ¡or solutions: 1 M (mol/L). Note : diFFerent convention in some biochemistry applications… – ¡or liquids and solids: pure liquid or solid – ¡or elements: The Form in which the element exists under conditions oF 1 atm and 298 K. Defnitions (cont.) • Standard elemental states (cont.): – Hydrogen: H 2 (g) (not atomic H) – Oxygen: O 2 (g) – Carbon: C (gr)..graphite as opposed to diamond • We will denote the standard state using the superscript “°”....
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This note was uploaded on 01/18/2012 for the course CHEM 152A taught by Professor Chiu during the Fall '12 term at University of Washington.

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Lec06_drobny_11 - Lecture 6: Standard Enthalpies •...

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