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Lecture5 - Lecture 5 Standard Enthalpies • Reading...

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Unformatted text preview: Lecture 5: Standard Enthalpies • Reading: Zumdahl 9.6 • Outline – What is a standard enthalpy? – Defining standard states. – Using standard enthalpies to determine D H° rxn 1 • 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 ∆H rxn ? A + B = C 10 KJ D + 5B = 3C + 4F 20 KJ 2K + B = 2F 50 KJ 3A + 4K = D + X KJ 2 CO (g) + 1/2O 2 (g) = CO 2 (g) D H = ?? (a): C (gr) + 1/2O 2 (g) = CO (g) D H = -110.5 kJ/mol (b): C (gr) + O 2 (g) = CO 2 (g) D H = -393.5 KJ/mol -(a): CO (g) = C (gr) + 1/2O 2 (g) D H = +110.5 kJ/mol (b): C (gr) + O 2 (g) = CO 2 (g) D H = -393.5 KJ/mol CO (g) + C (gr) + O 2 (g) = CO 2 (g) + C (gr) + 1/2O 2 (g) D H = -393.5 + 110.5 KJ/mol 1/2 3 CO (g) + 1/2O 2 (g) = CO 2 (g) D H = ?? C (gr) + 1/2O 2 (g) D H = -110.5 kJ/mol D H = -393.5 + 110.5 KJ/mol C (gr) + O 2 (g) D H = -393.5 kJ/mol 4 Definition of ΔH° f • Standard Enthalpy of Formation , ΔH° f : “The change in enthalpy that accompanies the formation of 1 mole of a compound from its elements with all substances at standard state .” Going from where to where? element1 + element2 + element3 = compound A (Standard state) (Standard state) (Standard state) (Standard state) (1 mole) Design this reaction: ΔH rxn = ΔH° f 5 What is Standard State ?...
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Lecture5 - Lecture 5 Standard Enthalpies • Reading...

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