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Lecture 6 1-18-08 Heats of Formation

Lecture 6 1-18-08 Heats of Formation - Lecture...

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Lecture Demonstration Reaction of Na with H 2 O •What are the products of the reaction? •What are the signs of q, w, Δ E and Δ H •Compare Δ E and Δ H. Why and how do the differ

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Heats of Reaction from Standard Enthalpies of Formation The enthalpy change of a reaction is equal to the total formation enthalpy of the products minus that of the reactants. is the mathematical symbol meaning “the sum of”, and m and n are the coefficients of the substances in the chemical equation . . ( ) ( ) nts reacta H m products H n H f f Δ Δ = Δ 0 0 0
A Problem to Consider Large quantities of ammonia are used to prepare nitric acid according to the following equation: 4 NH 3 (g) + 5 O 2 (g) 4 NO(g) + 6 H 2 O(g) What is the standard enthalpy change, Δ H 0 for this reaction?

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A Problem to Consider 4 NH 3 (g) + 5 O 2 (g) 4 NO(g) + 6 H 2 O(g) Δ H 0 = 4 Δ H f 0 (NO) + 6 Δ H f 0 (H 2 O) - 4 Δ H f 0 (NH 3 ) - 5 Δ H f 0 (O 2 ) Δ H 0 = [4(90.3) + 6(-241.8) -4(-45.9) -5(0)] kJ Δ H 0 = -906 kJ Why does this work? Construct an indirect pathway between initial and final states that goes through standard states and is equivalent to the direct reaction Products (final state) - Reactants (initial state)

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