It has been suggested that Electrode potential be merged into this article or section. (Discuss)

It has been suggested that Reduction potential be merged into this article or section. (Discuss)

Introduction: Image File history File links Please see the file description page for further information. ... This article may be too technical for most readers to understand. ... Image File history File links Please see the file description page for further information. ... Reduction Potential Reduction Potential is defined as the tendency of a species to acquire electrons and be reduced. ...

The basis for an electrochemical cell such as the galvanic cell is always a redox reaction which can be broken down into two half-reactions: oxidation at anode (loss of electron) and reduction at cathode (gain of electron). Electricity is generated due to electric potential created as a result of difference between individual potentials of the two metal electrodes at the cathode and at the anode terminals. Although the overall potential of a cell can be measured, there is no way to measure the individual potentials of the electrodes in isolation. The electric potential also varies with temperature, concentration and pressure. The standard electrode potential (abbreviated E⁰) is the measure of individual potential of any electrode at standard conditions (temperature 298K, solutes at 1 M and gases at 1 atm). Since the oxidation potential of a half-reaction is the negative of the reduction potential in a redox reaction, it is sufficient to calculate either one of the potentials. Therefore, standard electrode potential is commonly written as standard reduction potential. An electrochemical cell is a setup used for creating an electromotive force(voltage) in a conductor separating two reactions. ... The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ... The most fundamental reactions in chemistry are the redox processes. ... A half reaction is either the oxidation or reduction reaction component of a redox reaction. ... The most fundamental reactions in chemistry are the redox processes. ... Reduction or reducing has several meanings: In mathematics, reduction is the process of manipulating a series of equations or matrices into a desired simpler format. ... Electricity is a property of matter that results from the presence of electric charge. ... Electric potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. ... Alternative meanings: There is also an Electric-type Pokémon named Electrode. ... Temperature and air pressure can vary from one place to another on the Earth, and can also vary in the same place with time. ...

Calculation of Standard Electrode Potential:

As noted before, in order to overcome the difficulty of measuring individual potential of an electrode, the electrode of unknown reduction potential at anode can be paired with a cathode whose potential is set to zero. Such a zero potential electrode, called the standard hydrogen electrode, consists of a platinum electrode in contact with 1 M H⁺ ions and bathed by hydrogen gas at 1 atm. Given that the potential of cathode (reduction half-reaction) is set to be zero, the potential at the anode (oxidation half-reaction at the unknown electrode) can be measured. For example, to measure the standard reduction potential of zinc metal electrode, an electrochemical cell can be built with the anode compartment containing zinc metal electrode in 1 M ZnSO₄ solution. The anode oxidation half-reaction is then: Image File history File links Download high resolution version (1600x1065, 185 KB) Summary http://wps. ... A standard hydrogen electrode (abbreviated SHE) is a redox electrode which is placed in the basis of the thermodynamic scale of oxidation-reduction potentials. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ...

Zn_(s) → Zn²⁺_(aq) + 2e^-

The electrons produced at the anode flow through the wire and at the cathode, the reduction half-reaction occurs as follows: Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ...

2H⁺_(aq) + 2e^- → H_2(g)

Where concentration of H⁺ is 1 M and pressure of H₂ gas is at 1 atm. The line notation for this cell is:

Zn_(s) | Zn²⁺_(aq),(1M) || 2H⁺_(aq) | H_2(g),(1atm)

Since the reduction half-reaction has a potential of zero, the reading of the voltmeter E⁰_cell (or EMF) corresponds to the potential of the zinc metal because: Two digital voltmeters A voltmeter is a measuring instrument for measuring the voltage between two points in an electric circuit. ... EMF stands for: electromotive force (voltage) electromagnetic field the U.K. band EMF Electronic Music Foundation Microsoft Enhanced Metafile Eclipse Modeling Framework EMF Broadcasting (Educational Media Foundation) Extreme Measures Federation (online pro-wrestling fantasy league) Categories: Disambiguation | TLAs ...

E^o_cell(0.76V)= E^o_2H⁺(aq) → H_2(g)(0V) + E^o_Zn(s) → Zn²⁺_(aq)(0.76V)

where the superscript ^o denotes the standard states that are employed. Through this way, the standard reduction potentials for common electrodes can be measured. (See Table of standard electrode potentials) The values below are standard electrode potentials taken at 25°C in aqueous solution. ...

Since the conventional values are given as reduction potentials, in combining two half-reactions in a redox reaction, the sign of the known reduction potential for the metal electrode being oxidized must be reversed. Also, since the number of electrons lost must equal the number gained, the half-reactions must be balanced by multiplying with an integer. However, the value of standard reduction potential is independent of the number of times the reaction occurs. Thus the value of E⁰_cell is not changed when the half-reactions are multiplied by an integer.

The Standard Reduction Potential table:

Since the values are given in their ability to be reduced, the bigger the standard reduction potentials, the easier they are to be reduced, in other words, they are simply better oxidizing agents. For example, F₂ has 2.87V and Li⁺ has -3.05V. F₂ reduces easily and is therefore a good oxidizing agent. In contrast, Li⁺ would rather undergo oxidation (hence a good reducing agent). Thus Zn²⁺ whose standard reduction potential is -0.76V can be oxidized by any other electrode whose standard reduction potential is greater than -0.76V (eg. H⁺(0V), Cu²⁺(0.16V), F₂(2.87V)) and can be reduced by any electrode with standard reduction potential less than -0.76V (eg. H₂(-2.23V), Na⁺(-2.71V), Li⁺(-3.05V)). Image File history File links Download high resolution version (1467x1200, 226 KB) Summary http://wps. ... A reducing agent is the element or a compound in a redox (reduction-oxidation) reaction ( see electrochemistry ) that reduces another species. ... In ring theory, a ring R is said to be reduced if it has no non-zero nilpotent elements. ...

In a galvanic cell, where a spontaneous redox reaction drives the cell to produce an electric potential, Gibbs free energy ΔG⁰ must be negative. For spontaneous, see Spontaneous bacterial peritonitis Spontaneous combustion Spontaneous emission Spontaneous fission Spontaneous human combustion Spontaneous Music Ensemble Spontaneous order Spontaneous process Spontaneous reaction Spontaneous remission Spontaneous symmetry breaking This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... In thermodynamics the Gibbs free energy is a thermodynamic potential and is therefore a state function of a thermodynamic system. ...

(If E^o_cell> 0, we have a spontaneous process (galvanic cell)

If E^o_cell< 0, we have a nonspontaneous process (electrolytic cell)) Electrolytic cells are composed of an electrolyte (usually water or another solvent capable of dissolving various ions of interest), a cathode and an anode. ...

ΔG⁰_cell is related to E⁰_cell by the equation:

ΔG⁰_cell = -nFE⁰_cell

where n is number of moles of electrons per mole of products The word mole when used alone, has several possible meanings in the English language: Mole (animal): a small burrowing mammal. ...

F is the Faraday constant, ~96,485 C/mol In physics and chemistry, the Faraday constant is the amount of electric charge of one mole of electrons. ...

Thus in order to have a spontaneous reaction (-ΔG⁰), E^o_cell must be positive, where

E^o_cell= E^o_anode + E^o_cathode

where E⁰_anode is the standard potential at the anode (reverse the sign of the standard reduction potential value for the electrode) and E⁰_cathode is the standard potential at the cathode as given in the table of standard electrode potential.

Non-standard condition:

The standard electrode potentials are measured at standard conditions. Yet in most cases, real cells may operate under non-standard conditions. Given the standard potential of the cell, the non-standard cell potential can be calculated using the Nernst equation: In electrochemistry, the Nernst equation gives the electrode potential (E), relative to the standard electrode potential, (E0), of the electrode couple or, equivalently, of the half cells of a battery. ...

E_cell= E^o -

External Links

• Standard Hydrogen Potential [1]
• Redox Equilibria [2]
• Chemistry of Batteries [3]
• Electrochemical reactions [4]

References

Zumdahl, Steven S.; Zumdahl, Susan A. (2000). Chemistry (5th ed.), Houghton Mifflin Company. ISBN: 0-395-98583-8

Atkins, Peter; Jones, Loretta. (2005). Chemical Principles(3rd ed.), W.H. Freeman and Company. ISBN:0-7167-5701-X