Combust&Arson

Combust&Arson - Chapters9&10 &Arson...

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 4/10/11 Bell Text (Chapter 9) Girard Text (Chapter 10)
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 4/10/11 Introduction Arson crimes are difficult to solve Vandalisms is the leading cause of arson Approximately 25% of all arson fires are  drug related
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 4/10/11 Oxidation Reactions of Arson  Fire is the result of an oxidation reaction in which  a substance is burned in the presence of oxygen  (oxygen source can be NaHClO, KClO3, NH4NO3  as used in pipe bombs) CH4 + 2O2   CO2 + 2H2O Oxidation reactions can be differentiated  according to their rate: Slow (controlled):  rusting and bleaching
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 4/10/11 Oxidation-Reduction  An  oxidation  occurs  when an atom or ion  loses  electrons. reduction  occurs  when an atom or ion  gains  electrons. One cannot occur 
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 4/10/11 Oxidation Numbers To determine if an oxidation-reduction reaction  has occurred, we assign an  oxidation number  to  each element in a neutral compound or charged  entity.
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 4/10/11 Oxidation Number Rules Elements in their elemental form have an oxidation  number of zero. The oxidation number of a monatomic ion is the  same as its charge. Nonmetals tend to have negative oxidation  numbers, although some are positive in certain  compounds or ions. Oxygen has an oxidation number of −2, except in the  peroxide ion (O22-) in which it has an oxidation number of −1. Hydrogen is −1 when bonded to a metal, +1 when 
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 4/10/11 Oxidation Number Rules Nonmetals tend to have negative oxidation  numbers, although some are positive in certain  compounds or ions. Fluorine always has an oxidation number of −1. The other halogens have an oxidation number of −1 when  they are negative; they can have positive oxidation  numbers, however, most notably in oxyanions (ClO-). The sum of the oxidation numbers in a neutral  compound is zero. The sum of the oxidation numbers in a polyatomic 
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 4/10/11 Oxidation Number Practice  Determine the oxidation number for the indicated  element in each of the following compounds: A. Sn in SnCl3- A. Cl in KClO3 A. Br in HBrO
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 4/10/11 Principles of Combustion  Combustion reactions are spontaneous  chemical reactions Spontaneous chemical reactions require that the  potential energy in the bonds of the products be  more than the reactants CH4 + 2O2 7   CO2  + 2H2O  + heat energy Complete combustion produces the above  products; incomplete combustion produces CO,  soot
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Combust&Arson - Chapters9&10 &Arson...

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