University:
Eastern Kentucky University
Course:
CHE 111 | General Chemistry
Academic year:

2020
Views:

284

Pages:

1
Author:

ui4s3l4md25

General Chemistry 12: Electrochemistry Galvanic Cell Electrochemical Cells Anode: Always the site of oxidation. It attracts anions. Cathode: Always the site of reduction. It attracts cations. Electrolytic Cell Emf & Thermodynamics Electromotive force and change in free energy always have OPPOSITE signs. Red Cat = Reduction at the Cathode Concentration Specialized form of galvanic cell in which both electrodes are Cells: made of the same material. It is the concentration gradient between the two solutions that causes mvmt of charge. Rechargeable Can experience charging (electrolytic) and discharging Batteries: (galvanic) states. Lead-Acid: Discharging: Pb anode, PbO2 cathode in a concentrated sulfuric acid solution. Low energy density. DG ° Galvanic + - - + Concentration 0 0 Current Flow: Cathode ® Anode Electrolytic Cells: House non-spont reactions. +DG, -Emf, -𝐸°%#&& Anode = POS, Cathode = NEG 𝑬°𝐜𝐞𝐥𝐥 Electrolytic e- Flow Anode ® Cathode ° Galvanic Cells: House spontaneous reactions. -DG, +Emf, +𝐸%#&& (Voltaic) Anode = NEG, Cathode = POS ° Type of Cell ° ° 𝐸%#&& =𝐸"#$,%-./0$# ∆𝐺° ° −𝐸"#$,-20$# ° =−𝑛3F3𝐸%#&& ∆𝐺° =−R3𝑇3ln3(𝐾>? ) ∆𝐺 =3 ∆𝐺° +R3𝑇3ln3(𝑄) Faraday constant (F): 96,485 C 13C= E F Ni-Cd: Discharging: Cd anode, NiO(OH) cathode in a concentrated KOH solution. Higher energy density than lead-acid batteries. NiMH: More common than Ni-Cd because they have higher energy density. Describes the relationship between the concentration of species in a solution under nonstandard conditions and the emf. Cell Potentials Reduction Potential: Quantifies the tendency for a species to gain eand be reduced. More positive Ered = greater tendency to be reduced. Standard Reduction Potential: Nernst Equation ° 𝐸"#$ . Calculated by comparison to the standard hydrogen electrode (SHE). ° Standard Electromotive Force: 𝐸%#&& . The difference in standard reduction potential between the two half-cells. ° Galvanic Cells: +𝐸%#&& ° Electrolytic Cells: -𝐸%#&& When Keq > 1, then +𝐸°%#&& When Keq < 1, then -𝐸°%#&& =0 When Keq = 1, then 𝐸°%#&& GH ° 𝐸%#&&=𝐸%#&& −3 ln3(𝑄) IJ ° −3 𝐸%#&&=𝐸%#&& K.KMNO I log3(𝑄)