Nov_07 - Enthalpy of Formation Standard States Definitions of Standard States Gases gas at partial pressure of 1 atm Solutes a conc of 1M at an

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Enthalpy of Formation
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Standard States Definitions of Standard States : • Gases: gas at partial pressure of 1 atm • Solutes: a conc. of 1M at an applied P of 1atm • Pure liquids or solids: the pure liquid or solid • Elements: the elemental form that exists at 1 atm
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Standard Enthalpy of Formation ( H f °) ∆Η f º - enthalpy change for the formation of 1 mole of a compound from its elements all at standard states H f º for an element in its standard state equals zero • Normally reported in kJ per mole of the compound • There is no standard temperature. ∆Η f º depends on temperature and is often reported for 298 K
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reactants → products ΔHº reaction ΔHº reaction = Σ ΔH f º (products) – Σ ΔH f º (reactants)
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H Δ f º - example e.g. Calculate Hº Δ reaction at 298 K for : 4 NH 3 (g) + 7 O 2 (g) -----> 4 NO 2 (g) + 6 H 2 O(l) Look up in table of H Δ f º values at 298 K: H Δ f º (NH 3 (g)) = - 46 kJ/mol H Δ f º (O 2 (g)) = 0 kJ/mol <----- Definition H Δ f º (NO 2 (g)) = 34 kJ/mol H Δ f º (H 2 O(l)) = - 286 kJ/mol Δ reaction
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This note was uploaded on 01/20/2011 for the course CHEM 154 CHEM 154 taught by Professor Yang during the Spring '10 term at The University of British Columbia.

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Nov_07 - Enthalpy of Formation Standard States Definitions of Standard States Gases gas at partial pressure of 1 atm Solutes a conc of 1M at an

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