Chapter18_LEC - Chapter 18 Electrochemistry 2007, Prentice...

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Unformatted text preview: Chapter 18 Electrochemistry 2007, Prentice Hall Chemistry: A Molecular Approach , 1 st Ed. Nivaldo Tro Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Tro, Chemistry: A Molecular Approach 2 Redox Reaction one or more elements change oxidation number all single displacement, and combustion, some synthesis and decomposition always have both oxidation and reduction split reaction into oxidation half-reaction and a reduction half-reaction aka electron transfer reactions half-reactions include electrons oxidizing agent is reactant molecule that causes oxidation contains element reduced reducing agent is reactant molecule that causes reduction contains the element oxidized Tro, Chemistry: A Molecular Approach 3 Oxidation & Reduction oxidation is the process that occurs when oxidation number of an element increases element loses electrons compound adds oxygen compound loses hydrogen half-reaction has electrons as products reduction is the process that occurs when oxidation number of an element decreases element gains electrons compound loses oxygen compound gains hydrogen half-reactions have electrons as reactants Tro, Chemistry: A Molecular Approach 4 Rules for Assigning Oxidation States rules are in order of priority 1. free elements have an oxidation state = 0 Na = 0 and Cl 2 = 0 in 2 Na(s) + Cl 2 (g) 2. monatomic ions have an oxidation state equal to their charge Na = +1 and Cl = -1 in NaCl 3. (a) the sum of the oxidation states of all the atoms in a compound is 0 Na = +1 and Cl = -1 in NaCl, (+1) + (-1) = 0 Tro, Chemistry: A Molecular Approach 5 Rules for Assigning Oxidation States 1. (b) the sum of the oxidation states of all the atoms in a polyatomic ion equals the charge on the ion N = +5 and O = -2 in NO 3 , (+5) + 3(-2) = -1 2. (a) Group I metals have an oxidation state of +1 in all their compounds Na = +1 in NaCl 1. (b) Group II metals have an oxidation state of +2 in all their compounds Mg = +2 in MgCl 2 Tro, Chemistry: A Molecular Approach 6 Rules for Assigning Oxidation States 1. in their compounds, nonmetals have oxidation states according to the table below nonmetals higher on the table take priority Nonmetal Oxidation State Example F-1 CF 4 H +1 CH 4 O-2 CO 2 Group 7A-1 CCl 4 Group 6A-2 CS 2 Group 5A-3 NH 3 Tro, Chemistry: A Molecular Approach 7 Oxidation and Reduction oxidation occurs when an atoms oxidation state increases during a reaction reduction occurs when an atoms oxidation state decreases during a reaction CH + 2 O CO + 2 H O-4 +1 +4 2 +1 -2 oxidation reduction Tro, Chemistry: A Molecular Approach 8 OxidationReduction oxidation and reduction must occur simultaneously if an atom loses electrons another atom must take them the reactant that reduces an element in another reactant is called the reducing agent the reducing agent contains the element that is oxidized...
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Chapter18_LEC - Chapter 18 Electrochemistry 2007, Prentice...

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