ChE102_Notes_-_Chap_2

# ChE102_Notes_-_Chap_2 - ChE102 Div 9 10 Fall 2009 CHAPTER 2...

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ChE102 – Div 9 & 10 Fall 2009 CHAPTER 2 – Chemical Reactions Petrucci: 4.1-4.5 Some Reaction Definitions A Chemical Reaction is a process by which a chemical change occurs Reactants – substances that are transformed Products – substances that are produced Evidence of a chemical reaction: o o o o The Chemical Equation Chemical equations describe the changes that occur in chemical reactions: N 2 O 5 NO 2 + O 2 Chemical equations must be balanced , so that the number of atoms on the reactant side are equal to the number of atoms on the product side: Stoichiometric chemical equation describes only the net changes taking place in a reaction and does not necessarily correspond to what occurs at the molecular level The Mechanistic Equation Mechanistic equations describe the steps required to go from reactants to products at the molecular level For the above equation, a possible mechanistic equation could be: 2 N 2 O 5 2 NO 2 + 2 NO 3 NO 3 + NO 2 NO + NO 2 + O 2 NO 3 + NO 2 NO 2 . 2 N 2 O 5 4 NO 2 + O 2 Mechanistic equations must add up to the stoichiometric chemical equation. Chapter 2 1

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ChE102 – Div 9 & 10 Fall 2009 Stoichiometric Calculations Stoichiometric relationships are used to calculate the proportions of atoms in a molecule or the proportions of products and reactants in a given chemical reaction For the reaction: aA + bB cC + dD For example, 2N 2 O 5 4NO 2 + O 2 2 moles N 2 O 5 : 4 moles NO 2 : 1 mole O 2 EXAMPLE 1
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