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A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. Often, the concept of half reactions is used to describe what occurs in an electrochemical cell, such as a Galvanic cell battery. Half reactions can be written to describe both the metal undergoing oxidation (known ...
Electrode potentials of successive elementary half-reactions cannot be directly added. However, the corresponding Gibbs free energy changes (∆G°) must satisfy ∆G° = – z FE°, where z electrons are transferred, and the Faraday constant F is the conversion factor describing Coulombs transferred per mole electrons. Those Gibbs free energy ...
The electric potential also varies with temperature, concentration and pressure. 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.
In electrochemistry, the Nernst equation is a chemical thermodynamical relationship that permits the calculation of the reduction potential of a reaction (half-cell or full cell reaction) from the standard electrode potential, absolute temperature, the number of electrons involved in the redox reaction, and activities (often approximated by concentrations) of the chemical species undergoing ...
In the above equation, the Iron (Fe) has an oxidation number of 0 before and 3+ after the reaction. For oxygen (O) the oxidation number began as 0 and decreased to 2−. These changes can be viewed as two "half-reactions" that occur concurrently: Oxidation half reaction: Fe 0 → Fe 3+ + 3e −; Reduction half reaction: O 2 + 4e − → 2 O 2−
The anode oxidation half-reaction is Al + 3OH − → Al(OH) 3 + 3e − +2.31 V. The cathode reduction half-reaction is O 2 + 2H 2 O + 4e − → 4OH − +0.40 V. The total reaction is 4Al + 3O 2 + 6H 2 O → 4Al(OH) 3 +2.71 V. About 1.2 volts potential difference is created by these reactions and is achievable in practice when potassium ...
If zinc chloride is substituted for ammonium chloride as the electrolyte, the anode reaction remains the same: Zn + 2 Cl − → ZnCl 2 + 2 e −. and the cathode reaction produces zinc hydroxide and manganese(III) oxide. 2 MnO 2 + ZnCl 2 + H 2 O + 2 e − → Mn 2 O 3 + Zn(OH) 2 + 2 Cl −. giving the overall reaction Zn + 2 MnO 2 + H 2 O → ...
A half-metal is any substance that acts as a conductor to electrons of one spin orientation, but as an insulator or semiconductor to those of the opposite orientation. Although all half-metals are ferromagnetic (or ferrimagnetic), most ferromagnets are not half-metals. Many of the known examples of half-metals are oxides, sulfides, or Heusler ...