03 Notes - Spontaneous Redox

03 Notes - Spontaneous Redox - In order for a redox...

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Aim: What causes a redox reaction to occur spontaneously? QQ: Pb + NaNO 3 PbO + NaNO 2 a) Provide the half reactions b) Identify the oxidizing and reducing agent Do Now: When will reactions occur spontaneously? Spontaneous Reaction: reaction that leads to an overall decrease in energy (usually by decreasing enthalpy and increasing entropy). Reaction #1 Zn (s) + Cu 2+ (aq) Zn 2+ (aq) + Cu (s) Oxidation: Zn 0 Zn 2+ + 2e- Reduction: Cu 2+ + 2e- Cu 0 Reaction #2 Cu (s) + Zn 2+ (aq) Cu 2+ (aq) + Zn (s) Oxidation: Cu 0 Cu 2+ + 2e- Reduction: Zn 2+ + 2e- Zn 0 Why does the system with solid zinc and aqueous copper ions work while the reverse does not? Activity Series (See Reference Table J) The higher the metal, the more likely it is to be oxidized (better anode). The higher the nonmetal, the more likely it is to be reduced (better cathode).
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Unformatted text preview: In order for a redox reaction to occur spontaneously… • The more active metal (higher) is oxidized • The less active metal (lower) is reduced The opposite can occur, but will require energy Practice: Write the balanced, spontaneous redox reactions between the following pairs of metals and their ions. 1. Mn (s)/Mn 2+ (aq) and Ni (s)/Ni 2+ (aq) 2. Fe (s)/Fe 3+ (aq) and Pb (s)/ Pb 4+ (aq) 3. Au (s)/Au 3+ (aq) and Sn (s)/Sn 2+ (aq) Conclusions • Not all redox reactions will occur spontaneously • Use the activity series (table J) to predict spontaneity ▫ Metals towards the top need to be oxidized ▫ Metals towards the bottom need to be reduced • Non-spontaneous redox reactions can occur, but require energy to do so...
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This note was uploaded on 01/01/2012 for the course CHEM 101 taught by Professor Donahue during the Spring '11 term at Long Island U..

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03 Notes - Spontaneous Redox - In order for a redox...

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