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4) and dichromate (Cr 2 O 7 2−) anions are the principal ions at this oxidation state. They exist at an equilibrium, determined by pH: 2 [CrO 4] 2− + 2 H + ⇌ [Cr 2 O 7] 2− + H 2 O. Chromium(VI) oxyhalides are known also and include chromyl fluoride (CrO 2 F 2) and chromyl chloride (CrO 2 Cl 2). [6]
It is readily oxidized by the atmosphere. CrO is basic, while CrO 3 is acidic, and Cr 2 O 3 is amphoteric. [3] CrO occurs in the spectra of luminous red novae, which occur when two stars collide. It is not known why red novae are the only objects that feature this molecule; one possible explanation is an as-yet-unknown nucleosynthesis process. [4]
The oxidation states are also maintained in articles of the elements (of course), and systematically in the table {{Infobox element/symbol-to-oxidation-state}} See also [ edit ]
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Structure of CrO(O 2) 2 (pyridine).Hydrogen atoms bonded to carbon atoms are omitted. Color code: Cr = gray, C= black, H = white, O= red, N = blue. Chromium(VI) oxide peroxide is formed by the addition of acidified hydrogen peroxide solutions to solutions of metal chromates or dichromates, such as sodium chromate or potassium dichromate.
8, has been described as having a carbon oxidation state of − 8 / 3 . [19] Again, this is an average value since the structure of the molecule is H 3 C−CH 2 −CH 3, with the first and third carbon atoms each having an oxidation state of −3 and the central one −2.
For comparison of different reactions, all values of ΔG refer to the reaction of the same quantity of oxygen, chosen as one mole O (1 ⁄ 2 mol O 2) by some authors [2] and one mole O 2 by others. [3] The diagram shown refers to 1 mole O 2, so that e.g. the line for the oxidation of chromium shows ΔG for the reaction 4 ⁄ 3 Cr(s) + O 2 (g ...
The standard Gibbs free energy of formation (G f °) of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 bar of pressure and the specified temperature, usually 298.15 K or 25 °C).