Electrochemistry ZnSO4(aq) CuSO4(aq) Cu Zn Zn What will happen here? What will you see? Think about what will lose e- and what will gain. Can this setup light a light bulb or run a clock?

Electrochemistry Battery – uses the energy from a redox reaction to produce an electric current and do work. Electrochemistry – the study of the interchange of chemical and electrical energy.

Electrochemistry 2 Types of electrochemical processes The production of an electric current from a chemical (redox) reaction – battery, voltaic cell, galvanic cell. The use of an electrical current to produce a chemical change (redox reaction). Call this electrolysis. How do we harness this work to make a battery? When molecules collide, e- are transferred directly and no elec. Is produced. Key is to separate the oxid. And reducing agent so e- transfer will take place through a wire.

Electrochemistry How do we capture the energy? Separate the oxidizing agent (electron acceptor) from the reducing agent (electron donor) Requires the electron transfer to occur through a wire or an electric motor!

Figure 18.1: Schematic for separating the oxidizing and reducing agents in a redox reaction. Why is there no flow of electrons here? To get from the reducing agent to the oxidizing agent, the e- must travel through a wire. The current in the wire can be directed through a light or clock to do work. However in the above set up the electrons don’t flow. Why? 8H+ + MnO4- + 5e-  Mn2+ + 4H20 ; Fe2+  Fe3+ + e-

Figure 18.2: Electron flow. Build up of charges would require large amounts of energy Solutions must be connected to allow ions to flow E- flow in these conditions would lead to a build up of negative charge on the left and positive charge on the right, which will not occur without a large input of E. 8H+ + MnO4- + 5e-  Mn2+ + 4H20 ; Fe2+  Fe3+ + e-

Figure 18.4: The salt bridge contains a strong electrolyte. Figure 18.4: The porous disk allows ion flow. Salt bridge contains a strong electrolyte (define?) as a gell or sol., both ends are covered with a membrane often to allow only ions to pass. Porous disk – allows ion flow but not overall mixing.

Electrochemistry Want to allow ions to flow but not mix the solutions Electrons flow in the wire from reducing agent to oxidizing agent

Electrochemical battery (galvanic cell) A device powered by a redox reactions where the oxidizing agent is separated from the reducing agent so that the electrons must travel through a wire from reducing agent to oxidizing agent

Electrochemical battery (galvanic cell) Reducing agent loses electrons so it is oxidized Electrode where oxidation occurs is called the anode Oxidizing agent gains electrons and is reduced Electrode where reduction occurs is the cathode

Figure 18.5: Schematic of a battery. Anode - electrode where oxidation occurs Cathode – electrode where reduction occurs Complete picture of battery with ion flow, the circuit is completed Electron flow anode to cathode oxidation to reduction

Electrochemistry Go back to first cell with Zn and Cu and draw a voltaic cell. Label anode, cathode, and show direction of e- flow. Write out the two half reactions and then write out the complete reaction.

Cu/Zn Voltaic Cell Cu2+ + 2e-  Cu Cathode/reduction SO42- Zn2+ Cu2+ Zn2+ Cu2+ + 2e-  Cu Cathode/reduction Zn  Zn2+ + 2e- Anode/oxidation Cu2+ + Zn  Zn2+ + Cu

Electrochemistry