Presentation on theme: "Batteries Katy Swancutt ENGR 302I December 2007. What is a battery? It is something that converts chemical energy into electrical energy. They produce."— Presentation transcript:
Batteries Katy Swancutt ENGR 302I December 2007
What is a battery? It is something that converts chemical energy into electrical energy. They produce current via redox reactions: –Red=reduction (gaining electrons) –Ox=oxidation (losing electrons) Batteries are essentially Voltaic Cells connected in series.
What is a voltaic cell? Major components: Metals ZINC COPPER
What is a voltaic cell? Major components: Metals Electrolytes ZINC COPPER CuSO 4 (aq) ZnSO 4 (aq)
What is a voltaic cell? Major components: Metals Electrolytes “Salt Bridge” Wire ZINC COPPER CuSO 4 (aq) 1.0 Molar ZnSO 4 (aq 1.0 Molar WIRE AGAR Battery lifetime depends on the mass of metal in the electrodes.
What is a voltaic cell? ZINC COPPER CuSO 4 (aq) ZnSO 4 (aq) WIRE AGAR ANODE CATHODE
How does it make energy? The solid zinc anode oxidizes and becomes Zn 2+ Electrons travel through the wire toward the cathode The aqueous Cu 2+ is reduced and adds to the solid copper cathode
How much energy can it make? You can predict the voltage (direct current) between any two materials based on reduction potentials. A reduction potential, E o cell, is the difference between the standard reduction potential of the cathode (E o red(cathode) ) and the anode (E o red(anode) ). E o cell = E o red(cathode) -E o red(anode)
How much energy can it make? Step 1: Write the reaction. Zn (s) +Cu 2+ (aq) →Zn 2+ (aq) +Cu (s) Step 2: Look up values. E o red(cathode) = 0.337V E o red(anode) = V E o cell = 0.337V-(-0.763V) E o cell = 1.10V Actual voltage=1.044V Volts
How can you get more energy? 1.Connect several cells in series (1.044V+1.044V+1.044V…) 2.Work outside of standard conditions (concentration, temp, etc.) 3.Use different compounds for the electrodes. The greatest voltages are from a combination of the compound with the most negative potential (anode) and the most positive (cathode). These happen to be Li and F, respectively.
Electrode Combinations Below: Magnesium anode and Zinc cathode Expected V o cell =1.607V Observed V o cell =0.63V Above: Zinc anode and Iron III cathode Expected V o cell =1.534V Observed V o cell =0.70V
Electrode Combinations Above: Iron III anode and Copper cathode Expected V o cell =0.434V Observed V o cell =0.432V Below: Magnesium anode and Copper cathode Expected V o cell =2.707V Observed V o cell =1.923V
Electrode Combinations Above: Magnesium anode and Iron III cathode Expected V o cell =3.141V Observed V o cell =1.373V
Environmental Impacts Some electrodes are made of hazardous materials –Cadmium in Ni-Cd batteries –Lead in lead-acid batteries (like a car battery) –Mercury-electrode batteries (banned in 1996) –Arsenic and Antimony in lead-acid batteries
Environmental Impacts When batteries are not recycled, they ultimately end up contaminating soil, air, water, and finally end up in the food chain. Using secondary (rechargeable) batteries helps to prevent pollution.