Electrochemical Cells (Batteries) Chemical reaction produces electricity. Called “voltaic cells” Happens SPONTANEOUSLY.

Moving Electrons = Electricity Electrons from oxidized substance travel towards substance reduced. Traveling electrons move through “external circuit” where they do work.

Parts of a Simple Battery (Voltaic Cell) Made of Two “Half Cells” containing: 2 Metal Electrodes 2 Solutions of Ions External Wire Salt Bridge Zinc Copper Galvanic Cell: 2:30 https://www.youtube.com/watch?v=0oSqPDD2rMA

“Charge” (as either electrons or ions) flows in a “circuit” that is connected in a continuous loop. External Wire: allows ELECTRONS to flow between metal electrodes Salt Bridge: Allows IONS to flow between salt solutions

What is Ox/Red? Start with Table J Electrons travel from more “Active” metal toward less active metal. Metal above = oxidized Ion on Metal below = reduced Ex: Ox: Zn Red: Cu+2

flow in the external wire? Which way do electrons flow in the external wire? Electrons flow “Down Table J” From oxidized metal above to positive ion of metal below from Zn to Cu+2 e-

Which electrode is negative or positive? e- Electrons flow from negative to positive electrode. Negative electrode: Zn Positive electrode: Cu e-

Which electrode is the anode or cathode? Anode: metal electrode where oxidation occurs Ex: Zn Cathode: metal electrode where reduction occurs Ex: Cu Note: Electrodes are always pieces of pure metal (not ions)

Remember AN OX RED CAT Anode is where oxidation happens Cathode is where reduction happens

What are the Half Reactions? Ox: Zn0 Zn+2 + 2e- Red: Cu+2 + 2e- Cu0 What is the Net Equation? Net: (add ½ reactions) Zn0 + Cu+2 Zn+2 + Cu0 Make sure final net equation is balanced for electrons and atoms! Galvanic Cell Animation 2:00 https://www.youtube.com/watch?v=C26pH8kC_Wk e-

Which electrode gains/loses weight? Look at half reactions!! Which forms solid metal? Which forms dissolved ions? Ox: Zn0 Zn+2 + 2e- Red: Cu+2 + 2e- Cu0 Dissolved ion Solid metal

“The negative ions complete the circuit” Which way do the ions in the salt bridge “migrate” or move? Remember: “The negative ions complete the circuit” (The ions actually end up moving towards the solution of opposite charge that forms.) 1:30 https://www.youtube.com/watch?v=J1ljxodF9_g

Draw and label Battery Mg/Mg+2//Al+3/Al What is oxidized ________reduced_______ Neg. electrode_____ Positive electrode____ What is the anode _______cathode_______ Which way do e- flow in wire? To the ________ + ions flow _____ - ions flow _____in salt bridge? Table J Mg Al

Mg/Mg+2//Al+3/Al Battery Ox. Half Reaction: Red. Half Reaction: Net Equation: Which electrode gains mass ____ Which electrode loses mass ____

Means the reaction in the battery has Dead Battery Voltage = 0 Means the reaction in the battery has reached EQUILIBRIUM.

Practice  Given the balanced ionic equation representing the reaction in an operating voltaic cell: Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) The flow of electrons through the external circuit in this cell is from the (1) Cu anode to the Zn cathode (2) Cu cathode to the Zn anode (3) Zn anode to the Cu cathode (4) Zn cathode to the Cu anode

In the completed external circuit, the electrons flow from Given the balanced equation representing the reaction occurring in a voltaic cell: Zn(s) + Pb2+(aq) Zn2+(aq) + Pb(s) In the completed external circuit, the electrons flow from (1) Pb(s) to Zn(s) (2) Pb2+(aq) to Zn2+(aq) (3) Zn(s) to Pb(s) (4) Zn2+(aq) to Pb2+(aq)

Which statement is true for any electrochemical cell? (1) Oxidation occurs at the anode, only. (2) Reduction occurs at the anode, only. (3) Oxidation occurs at both the anode and cathode. (4) Reduction occurs at both the anode and cathode

Finding Voltage of a Battery (Honors) Use Voltage Table Find your half reactions and record voltage Note: All ½ reactions shown are reductions. For oxidation, reverse the sign of the voltage DO NOT multiply voltage by coefficients in balanced eq. http://employees.oneonta.edu/viningwj/sims/standard_potentials_s.html

Nerntz Equation (Honors)  

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