anode electrode at which an oxidation half-reaction occurs in an electrochemical cell
battery voltaic cell used to produce electricity through a chemical reaction
cathode electrode at which a reduction half-reaction occurs in an electrochemical cell
cell potential potential difference in volts of an electrochemical cell
cell voltage synonym for cell potential
corrosion oxidation of a metal by the action of air, water, and/or salt solutions
electric potential synonym for cell potential
electrochemical cell device in which electrons of a redox reaction pass through an electrical circuit
electrolytic cell electrochemical cell in which a nonspontaneous reaction is carried out by electrolysis
electromotive force (EMF) synonym for cell potential
galvanic cell electrochemical cell in which a spontaneous chemical reaction produces electricity
half-cell combination of reduced and oxidized forms of a given species upon which a redox equilibrium is established
nonspontaneous type of reaction when cell potential is negative
salt bridge device used to join two half-cells and containing a salt solution that permits the flow of ions between two half-cells
spontaneous type of reaction when cell potential is positive
voltaic cell synonym for galvanic cell
1. "Electrons can flow through solutions."
In "conduction of electricity" through solutions, electrons themselves do not pass through the solutions. Rather, charge balance is maintained in the solution by movement of cations and anions toward the electrodes where charge transfer takes place at the solution interface.
2. "Water is a good conductor of electricity."
Water is a very poor "conductor" of electricity. (Recall that the ionization constant for water is very small.) The reason it is dangerous to insert a light bulb while standing in a puddle of water is that water is a great solvent for ionic compounds. Tap water and fresh water typically contain dissolved ions in sufficient concentrations to enable the solution to be conductive. However, ions in solution carry the charge and are thereby responsible for the current, not the water itself.
3. "Only batteries are electrochemical cells."
Both voltaic and electrolytic cells are electrochemical cells. Voltaic cells produce electrical energy from differences in chemical potential energy. Electrolytic cells use electrical energy to produce products of higher chemical potential energy.
1. Half-cell reduction potentials and voltaic cell potentials are intensive properties like density and temperature. Therefore, they are independent of the quantity of material present. That is the reason why multiplying half-reactions by a constant in balancing a redox equation does not affect the value of the potential for the reaction. Because the half-cell potential is an intensive property, it does not change when the amount of reacting material is changed. This is different from Hess's Law calculations and other calculations of thermodynamic quantities such as enthalpy, entropy, and free energy. As extensive properties, they do depend on the amount of substance present.
2. The numeric value for an oxidation potential is the negative of the reduction potential. When you reverse the equation for a reduction reaction, it becomes an oxidation equation and the direction (i.e., the sign) of the potential changes.
3. When obtaining a reduction potential value in a standard table of half-reactions, the equation of interest must be identical to the one represented in the table. This includes phase (solid, liquid, gas, aqueous solution, etc.) as well as cases in which a precipitate might be involved such as the reduction of AgCl(s) to Ag(s) and Cl (aq). Often, standard tables contain several equations that are very similar but have different half-cell potentials. Also, be aware that the reduction potentials in standard tables are calculated from thermodynamic quantities. Actual values measured in the laboratory may vary from these standard values. If you are interested in reasons, refer to the concept of overvoltage in a college chemistry text.
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