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Redox Reactions. A special characteristic of many of the five types of reactions is the ability of elements to gain or lose electrons when they react with other elements. What is a redox reaction?.
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Redox Reactions A special characteristic of many of the five types of reactions is the ability of elements to gain or lose electrons when they react with other elements.
What is a redox reaction? Oxidation-reduction reaction: Any chemical reaction in which electrons are transferred from one atom to another; also called a redox reaction.
A Familiar Example When magnesium burns in the presence of oxygen, each Mg atom loses 2 electrons and each oxygen atom gains 2 electrons.
Another Redox Example Sodium and chloride react violently to form table salt, NaCl. Each Na atom loses 1 electron while each Cl atom gains 1 electron.
Some Basic Definitions Oxidation: The loss of electrons from the atoms of a substance; increases an atom's oxidation number. Reduction: The gain of electrons by the atoms of a substance; decreases an atom's oxidation number.
Origins of the Terminology Oxidation: came from observing combustion reactions in which whatever element combined with oxygen lost electrons. Reduction: came from observing metals being separated from oxygen, in which large amounts of metal ore were reduced to a much smaller and purer piece of metal.
Current Meaning of Oxidation-Reduction Now the terms oxidation and reduction are applied to any reaction in which electrons are lost and gained.
A Mnemonic Device to Remember the Processes LEO the lion says GER Lose Electrons Oxidation Gain Electrons Reduction
Two More Important Terms Oxidizing agent: The substance that oxidizes another substance by accepting its electrons. (The oxidizing agent is the substance that is reduced.) Reducing agent: The substance that reduces another substance by losing electrons. (The reducing agent is the substance that is oxidized.)
Just a Few Examples of Redox Reactions in Everyday Life Bleach to whiten clothes: sodium hypochlorite oxidizes dyes, stains, and other materials that discolor clothes stain molecules(s) + OCl-(aq) => colorless molecules(s) + Cl-(aq) Hydrogen peroxide: used as an antiseptic because it oxidizes some of the vital biomolecules of germs A redox reaction is what propels the space shuttle during its initial launch into space.
A Few More Examples Bioluminescence in fireflies and deep-sea fish is caused by redox reactions to release the energy stored up in chemical bonds Photography uses a series of redox reactions in the image capture and development processes Potassium chromate is used in breath analyzers to estimate alcohol content by observing the color of the chromate ion
Redox and Electonegativity Even in reactions where there are no ionic compounds present, that is, where there is no obvious transfer of electrons, we may still consider them to be redox reactions. In such reactions, we treat the more electronegative atom as if it is reduced by gaining electrons from the other atom. We treat the less electronegative atom as if it is oxidized by losing electrons.
Oxidation Numbers Oxidation numbers are tools that scientists use in writing chemical equations to help them keep track of the movement of electrons in a redox reaction. They are written with the positive or negative sign before the number, e.g. +2, -1. Oxidation numbers do not have an exact physical meaning, but they help indicate the general distribution of electrons among bonded atoms in a molecular compound or in a polyatomic ion.
Different Oxidation States Some elements, such as chromium, can have several different oxidation states, such that each oxidation state exhibits a different color.
Determining Oxidation Numbers We assign oxidation numbers based on definite rules in order to keep track of electron distributions in molecular as well as ionic compounds. (For the rules for determining oxidation numbers, see class handout.)
