Lecture 31 11072008 - Announcements Hf:enthalpy...

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Announcements
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Standard Heats of Formation Standard Heats of Formation ( H ° f ):  enthalpy  change for the formation of 1 mole of substance in  its standard state from its constituent elements in  their standard states. The standard heat of formation for any element in  its standard state is defined as being  ZERO . H ° f     =  0  for an element in its standard state Reference point from which all enthalpy changes are  measured
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Standard Heats of Formation
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Standard Heats of Formation Calculating  H °  for a reaction: H ° reaction  =  H ° (Products) –  H ° (Reactants) For a balanced equation, each heat of formation  must be multiplied by the stoichiometric coefficient. a A +  b B         c C +  d D H °  = [ c H ° f    (C) +  d H ° f    (D)] – [ a H ° f    (A) +  b H ° f   
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Standard Heats of Formation
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Standard Heats of Formation  Example Calculate  H °  (in kilojoules) for the reaction of  ammonia with O 2  to yield nitric oxide (NO) and  H 2 O( g ), a step in the Ostwald process for the  commercial production of nitric acid.
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