Cells and Voltage

Explain the operation of a voltaic (galvanic) cell at the visual, particulate and symbolic level Include: writing half-cell reactions and overall reaction Additional KEY Terms line notation anode cathode salt bridge

Electrical current made with spontaneous redox Volta (1745-1827) Electrical current made with spontaneous redox Half-cells are separated from each other Transfer of electrons forced through wire Load can be run with high enough voltage Voltaic cells (also called Galvanic cells) use a spontaneous redox reaction to convert chemical energy into electrical energy

Electric current (I) – a flow of electrons. e- move through conductors redox e- transferred between metal electrodes Voltage (V) – measure of e- ability to do work also called electrical potential (E°)

The following applies to ALL electrochemical cells node – electrode where xidation occurs o e- produced at anode negative electrode athode – where eduction occurs C r e- consumed at cathode positive electrode

2 Ag+(aq) + Cu(s) → 2 Ag(s) + Cu2+(aq) Electrons will be transferred from copper to silver

electrons move from anode to cathode ("A to C") Anode loses mass: e- are donated by metal ions dissolve in solution – (s) into (aq) Eventually, anode is completely oxidized to ions electrons move from anode to cathode ("A to C") Anode loses mass: e- are donated by metal ions dissolve in solution – (s) into (aq) anode slowly “used up” Cathode gains in mass: e- are accepted by cations cations are reduced – (aq) into (s) “Plate out” onto the cathode

You will have to completely label a diagram like this one

Salt bridge - maintains charge balance filled with an electrolyte solution (salt or acid) allows movement of ions, without mixing cells neutralizes half-cell products Ions build-up in both half-cells as the cell operates – if a cell solution gets too + or – electrons will stop moving through

The excess positive and negative ions in the solution are neutralized by the salt bridge ions allowing the redox reaction to continue

2 Ag+(aq) + Cu(s) → 2 Ag(s) + Cu2+(aq) Line notation a short hand notation of a voltaic cell. 2 Ag+(aq) + Cu(s) → 2 Ag(s) + Cu2+(aq)

An electrochemical cell with Cu (II) oxidizing Zn is constructed. Identify the anode and cathode. Write the net equation for the reaction. What direction do the electrons move? What is the line notation?

Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s) 1. Copper is the cathode – reduction. Zinc is the anode – oxidation. 2. Oxidation: Zn(s) → Zn2+(aq) + 2 e– Reduction: Cu2+(aq) + 2 e– → Cu(s) Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s) 3. e- move from zinc half-cell to copper half-cell. 4. Zn(s) / Zn2+(aq) // Cu2+(aq) / Cu(s)

CAN YOU / HAVE YOU? Explain the operation of a voltaic (galvanic) cell at the visual, particulate and symbolic level Include: writing half-cell reactions and overall reaction Additional KEY Terms line notation anode cathode salt bridge