Energy+Part+4 - 2 g 0.5O 2 g C → 2 H 5 OH l H ∆ o f =...

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Energy and Chemical Reactions – Part 4 Standard Heats of Reaction (∆H o rxn ) Standard States For a gas, the standard state is 1 atm and the gas behaving ideally. For a substance in aqueous solution, the standard state is 1 M concentration. For a pure substance (element or compound), the standard state is usually the most stable form of the substance at 1 atm and the temperature of interest, usually 298 K. Formation Equation – 1 mol of a compound forms from its elements. C(graphite) + 2H 2 ( g ) CH 4 ( g ) H o f = 74.9 kJ Na( s ) + 0.5Cl 2 ( g ) NaCl( s ) H o f = 411.1kJ 2C(graphite) + 3H
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Unformatted text preview: 2 ( g ) + 0.5O 2 ( g ) C → 2 H 5 OH( l ) H ∆ o f = 277.6kJ − • An element in its standard state is assigned a H ∆ o f = 0 • Most compounds have negative H ∆ o f (A compound is more stable than its component elements. H ∆ o rxn = ∑ m H ∆ o f(products) −∑ n H ∆ o f(reactants) Problem: Use the following information to find H ∆ o f of methanol. CH 3 OH( l ) + 3/2O 2 ( g ) CO → 2 ( g ) + 2H 2 O( g ) H ∆ o comb = 638.5 kJ − H ∆ o f of CO 2 ( g ) = 393.5 kJ / mol − H ∆ o f of H 2 O( g ) = 241.8kJ / mol −...
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This note was uploaded on 04/13/2008 for the course CHM 2045 taught by Professor Mitchell during the Fall '07 term at University of Florida.

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