Redox reactions can be in solutions {cell, redox reaction}|. Conducting plates can be in two connected half-cells. Current from one electrode goes through wire to other electrode and then through solution.
potential
Metal and metal ion have potential difference, because electrons and ions separate. If potential > 0, metal favors reduction. If potential < 0, metal favors metal oxidation.
Nernst equation
If electrode voltage is > 0, reaction is spontaneous. At equilibrium, voltage = 0 and current = 0.
tables
Tables can show reduction-half-reaction potentials. Hydrogen electrode has standard potential 0 V.
diffusion
In fast reactions, diffusion controls reaction rate. Moving electrode or stirring solution minimizes diffusion effects.
salt bridge
Agar and potassium-chloride salt bridge can connect half-cells.
membrane
Membranes that block and allow ion flows can have potential difference, because membrane sides have different ion concentrations. Membrane-permeable ion diffuses through until electrostatic repulsion from higher-concentration side stops ion flow.
Redox reaction has two parts {half-reaction}| {half-cell} that interact, reducing-agent oxidation and oxidizing-agent reduction. Cell redox reactions oxidize reducing agent and reduce oxidizing agent. For example, half-reaction for hydrogen electrode is 2 H+ + 2 e- [+ and - are superscripts] <-> 1 H2 [2 is subscript].
Potential difference produced by open circuit {electromotive force}| (emf) is voltage that can make electricity.
Devices that make electric current have resistance force {back electromotive force}| to current. Maximum battery power has battery back electromotive force equal to circuit resistance.
Voltage applied to cells {electrolytic cell}| can force current through cell and cause reverse redox reaction. In electrolytic cells, cathode is electron source, and anode is electron sink. Applying voltage and current can split molecules by electrolysis. For example, water can form hydrogen and oxygen. Aluminum salts can make aluminum.
Spontaneous redox reaction in cells {galvanic cell}| can make current. In galvanic cells, anode oxidizes and is negative, while cathode reduces and is positive. Metal or metal-oxide electrode can be in solution {wet cell} or paste {dry cell}. Different metal or metal oxide can be in same solution or paste, or another solution or paste connected to first by conductor, to make two coupled cells and a battery. Metal reacts with solution to make ions. Metal anode loses electrons and becomes positive. Metal cathode gains electrons and becomes negative. Electrodes have potential difference.
battery types
Batteries can have nickel and cadmium in acid solution. Edison cells have nickel oxide and iron electrodes in alkaline solution. Batteries can have lead and lead oxide in acid solution.
Galvanic cells {fuel cell}| can have continuous fuel supply. Fuel cells make electric current by oxidizing hydrides or other substances. Fuel cells are efficient, cool, and clean.
Electrolysis can put metal on conducting surfaces {electroplating}|. In silver plating, gold plating, and zinc plating, metal derives from salt solution. Electric current adds electrons to change ion to metal at electrode.
In electrolytic cells, oxidation is at positively charged electrode {anode, cell}|. In galvanic cells, reduction is at positively charged electrode.
In electrolytic cells, reduction is at negatively charged electrode {cathode, cell}|. In galvanic cells, oxidation is at negatively charged electrode.
5-Chemistry-Inorganic-Oxidation-Reduction
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Date Modified: 2022.0225