Oxidation Numbers As Determinants Of Oxidation-Reduction Reactions
Strings (SiPjAjk) = S7P5A52 Base Sequence = 12735 String Sequence = 12735 - 5 - 52
Figure 14.49 presents a heterogeneous synthesis reaction of sodium and chlorine.
This chemical reaction is also an oxidation-reduction reaction. Why?
S7P5A52 (Change - Chemical Change)
Pj Problem of Interest is of type change (chemical change).
The common meaning of burning is the combining of fuel with oxygen in air. However, burning can also occur in the absence of atmospheric oxygen. The type of reaction that allows burning to occur in the absence of atmospheric oxygen is called the oxidation-reduction reaction (also known as redox reaction).
The term oxidation was derived from the reaction of oxygen with other elements. Chemists later discovered that the process of oxidation was not unique to reactions with oxygen. In other words, other nonmetallic elements react with substances in a manner similar to that of oxygen. For example, Iron burns in fluorine. Hydrogen, sodium and antimony all burn in chlorine. The similarity in these reactions is that the element that is burning loses electrons. Consequently, chemists decided to define oxidation as the loss of electrons from an atom or ion.
The term reduction originated from the reaction in which oxide ores were reduced to their respective metals by removing oxygen from the ores, a process in which the metals gain eletrons. When chemists discovered that non oxides can also be reduced, they decided to define reduction as the gain of electrons by an atom or ion.
In general, oxidation can be described as de-electronation (loss of electrons) and reduction as electronation (gain of electrons). Usually, in ordinary oxidation-reduction reactions (redox), both processes occur simultaneously, sometimes by direct transfer of electrons from the atoms that are oxidized to those that are reduced. The substance in a redox reaction that gives up electrons is called the reducing agent while the substance that gains electrons is called the oxidizing agent. The reducing agent contains the atoms that are oxidized (the atoms that lose electrons) while the oxidizing agent contains the atoms that are reduced (the atoms that gain electrons).
The transfer of electrons between atoms during a chemical reaction is used to determine the occurrence of a redox reaction. This determination is carried out by analyzing changes in the oxidation numbers of the participating atoms in the chemical reaction. The following general rules are helpful rules used in the determination of changes in the oxidation numbers of atoms in a redox reaction:
(1) The oxidation number of any free element is 0. This statement is applicable to all atomic and molecular structures whether they are monoatomic, diatomic or polyatomic.
(2) The oxidation number of a monoatomic ion is equal to the charge on the ion. For example, Na+, Ca2+, Al3+ and Cl- have oxidation numbers of 1+, 2+, 3+ and 1- respectively. Some atoms such as Iron (Fe) and Tin (Sn) have more than one oxidation number. Fe can be either 2+ or 3+; Sn, 2+ or 4+.
(3) The oxidation number of each hydrogen atom in most of its compound is 1+. In compounds, such as lithium hydride (LiH) in which hydrogen is the more electronegative atom, its oxidation number is 1-
(4) The oxidation number of oxygen in most of its compounds is 2-. In peroxides (Na2O2, H2O2), each oxygen is assigned an oxidation number of 1-.
(5) The sum of the oxidation numbers of all the atoms in a substance must equal the apparent charge of the substance.
(6) In compounds, the elements of Group 1 (1A), Group 2 (IIA), and Aluminum have positive oxidation numbers of 1+, 2+, and 3+, respectively.
The given reaction presented in figure 14.49, 2Na(cr) + Cl2(g) -> 2NaCl(cr)
is a reaction in which sodium reacts with chlorine to produce sodium chloride. As a reactant, each sodium atom has an oxidation number of 0. In the product, the oxidation number of each sodium atom is 1+. As a reactant, each chlorine atom has an oxidation number of 0. In the product, each chlorine atom has an oxidation number of 1-. The changes in oxidation numbers implies that sodium has been oxidized because it is the element that has lost an electron (the reducing agent). Chlorine has been reduced because it has gained an electron (the oxidizing agent). So the reaction is a redox reaction.
Redox reactions are important components of many chemical reactions. They are present in the corrosion of metals, most forms of energy productions and many life processes that involve the transfer of electrons.
The point . is a mathematical abstraction. It has negligible size and a great sense of position. Consequently, it is front and center in abstract existential reasoning.
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