Name: oxidation states in redox reactions
Uploaded: 2020-03-26T07:22:24.000Z
Duration: 4 min 56 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.9

CHEM.9.B

Redox Reactions

Redox, que es la abreviatura de reducción-oxidación, es un tipo de reacción química clasificada por la transferencia neta de electrones. En esta reacción, una molécula pierde electrones, lo que se denomina oxidación, y la otra molécula gana electrones, lo que se denomina reducción.
Para ayudarlo a diferenciar entre los dos, recuerde la frase 'OIL-RIG', que significa 'la oxidación es perder, la reducción es ganar'. La molécula que se oxida se llama agente reductor porque reduce el otro reactivo. Del mismo modo, la molécula que se reduce se denomina agente oxidante porque oxida a la otra molécula.
Ahora que tenemos la terminología ordenada, veamos un ejemplo de una reacción redox, la formación del mineral óxido de magnesio. Durante la reacción, cada átomo de magnesio pierde dos electrones. Por lo tanto, el magnesio se oxida. Cada átomo de oxígeno gana dos electrones; Por lo tanto, el oxígeno se reduce.
Sin embargo, no todas las reacciones son reacciones redox. Por ejemplo, la reacción del óxido de calcio con el dióxido de carbono para formar carbonato de calcio no es una reacción redox. Entonces, ¿cómo podemos identificar una reacción redox?
Para ello, realizamos un seguimiento del número de oxidación de cada elemento a medida que pasa de reactivo a producto. El número de oxidación es la carga hipotética que tendría un átomo si sus enlaces a diferentes elementos fueran iónicos, lo que significa que los electrones se asignan al átomo más electronegativo. La suma de los números de oxidación en una molécula es igual a su carga total.
Echemos un vistazo al óxido de magnesio. Es un compuesto neutro, por lo que la suma de los números de oxidación del magnesio y el oxígeno es igual a cero. El magnesio puede dar dos electrones, por lo que su número de oxidación es más dos. El oxígeno puede aceptar dos electrones, por lo que su número de oxidación es menos dos.
¿Qué tal la reacción? Los compuestos elementales neutros puros tienen un número de oxidación de cero. Por lo tanto, tanto el magnesio como el oxígeno comienzan con números de oxidación de cero. Los números de oxidación del magnesio y el oxígeno cambiaron durante la reacción, por lo que se trata de una reacción redox.
Ahora, veamos la reacción del carbonato de calcio que vimos anteriormente. Ambos reactivos son neutros, por lo que la suma de los números de oxidación de ambos compuestos es cero. Como vimos con el óxido de magnesio, el calcio tiene un número de oxidación de más dos y el oxígeno menos dos. Entonces, el carbono en la molécula de dióxido de carbono tiene un número de oxidación de más cuatro y cada oxígeno menos dos.
¿Qué te parece el producto? El calcio es más dos y el carbono más cuatro, al igual que en los reactivos. Cada oxígeno es menos dos, totalizando menos seis, con el número de oxidación neta cero. Dado que ninguno de los números de oxidación ha cambiado, no se trata de una reacción redox.
Ahora vamos a presentar los cuatro tipos de reacciones redox. La primera es una reacción de desplazamiento único, en la que un átomo desplaza a otro. Verás esto en una reacción de termita, donde un metal se reduce y el otro metal se oxida.
El siguiente tipo es una reacción de combustión, que se produce entre un combustible y un oxidante para formar productos oxidados y calor. Esto se ve en el laboratorio durante la combustión de metano con oxígeno cuando se usa un quemador Bunsen.
La tercera es una reacción de síntesis, en la que dos reactivos se combinan para formar un solo producto, como en la síntesis de amoníaco, donde el nitrógeno se combina con el hidrógeno para formar amoníaco.
Finalmente, el cuarto tipo es una reacción de descomposición, donde un reactivo absorbe suficiente energía para romper sus enlaces y formar compuestos más pequeños. Esto es lo que sucede con los fuegos artificiales, donde el clorato de potasio se descompone en cloruro de potasio y oxígeno después de calentarse.
En este laboratorio, realizará e identificará varios tipos de reacciones redox que transforman el cobre sólido en óxido de cobre y luego nuevamente en cobre sólido.

reacciones redox

<h4>Oxidación y reducción</h4>
Algunas reacciones químicas se pueden clasificar como reacciones de reducción-oxidación o reacciones redox. La oxidación es el proceso en el que la materia, como un átomo o una molécula iónica, pierde uno o más electrones, y la reducción es el proceso en el que la materia gana uno o más electrones.
<h4>Estados de oxidación</h4>
Cada átomo de una molécula tiene su propio estado de oxidación o número de oxidación. El estado de oxidación describe qué tan oxidada está una molécula en relación con su forma elemental libre. El estado de oxidación se expresa como la carga que tendría un átomo si cada uno de sus enlaces a otros elementos fuera puramente iónico. Esto significa que los electrones en el enlace se asignan al átomo más electronegativo. El estado de oxidación de un átomo en su forma elemental libre se define como 0.
Hay algunas reglas que se siguen para determinar el estado de oxidación. Los elementos del Grupo I y del Grupo II suelen tener estados de oxidación de +1 y +2, respectivamente. El hidrógeno y el oxígeno suelen tener estados de oxidación de +1 y -2, respectivamente, y los halógenos suelen tener un estado de oxidación de -1. Además, los estados de oxidación de los átomos de una molécula siempre se suman a la carga de la molécula. Por lo tanto, a menudo se puede deducir el estado de oxidación de un átomo no mencionado anteriormente. Por ejemplo, considere el dióxido de carbono (CO2), que es una molécula neutra. Si cada una de las dos moléculas de oxígeno contribuye con -2, el estado de oxidación del carbono debe ser +4 para cancelar el -4 de los oxígenos.
Para un enfoque más general, dibuje la estructura de Lewis de la molécula, identifique los enlaces entre diferentes átomos y asigne cada enlace al átomo más electronegativo. Luego, cuenta el número de electrones en cada átomo, y cada enlace contribuye con dos electrones. Reste el número de electrones que están actualmente en el átomo del número estándar de electrones de valencia para que ese átomo obtenga el número de oxidación.
Consideremos de nuevo el dióxido de carbono. Cada oxígeno tiene dos pares solitarios de electrones y está conectado al carbono central por un doble enlace. El oxígeno es más electronegativo que el carbono, por lo que cada enlace C = O, que representa cuatro electrones, se asigna a su oxígeno. Por lo tanto, a cada oxígeno se le asigna un total de ocho electrones (cuatro de los pares solitarios y cuatro del doble enlace), y al carbono no se le asigna ninguno. El número predeterminado de electrones de valencia para el oxígeno es seis, por lo que el número de oxidación para cada oxígeno es 6 – 8 = -2. El número predeterminado de electrones de valencia para el carbono es cuatro, por lo que el número de oxidación para el carbono es 4 – 0 = +4.
<h4>Reacciones redox</h4>
No todas las reacciones químicas se clasifican como reacciones redox. Una reacción redox es cualquier reacción en la que hay un cambio en el estado de oxidación de un átomo. Por lo tanto, para verificar si una reacción es una reacción redox, determine los estados de oxidación de cada átomo en los reactivos y productos y busque cualquier cambio.
Muchas reacciones redox implican una transferencia de electrones directamente de una molécula o átomo a otro. En esas reacciones, si una molécula, o átomo, gana un electrón, otra molécula, o átomo, debe perder un electrón. Una forma sencilla de recordar las definiciones de oxidación y reducción es a través de la frase OIL-RIG, que significa: Oxidación Is Losing – Reduction Is Gaining.
La molécula que gana un electrón se reduce, pero se llama oxidante o agente oxidante porque está oxidando a la otra molécula. Del mismo modo, la molécula que pierde un electrón se oxida, pero se llama agente reductor o reductor porque reduce la otra molécula.
Hay cuatro tipos principales de reacciones que suelen implicar procesos redox.
<ol>
	<li style="font-size:17px">Reacción de desplazamiento único: Un átomo desplaza a otro átomo que es parte de un compuesto, y lo reemplaza.</li>
	<li style="font-size:17px">Reacción de combustión: Un compuesto es reducido por un oxidante fuerte, típicamente gas oxígeno. Las reacciones de combustión que se producen entre los hidrocarburos y los compuestos orgánicos suelen producir dióxido de carbono y agua.</li>
	<li style="font-size:17px">Reacción de síntesis: Dos reactivos forman un solo producto.</li>
	<li style="font-size:17px">Reacción de descomposición: Un solo reactivo se rompe en dos o más productos.</li>
</ol>
<h4>Referencias</h4>
1. Harris, D. C. (2015). Análisis químico cuantitativo. Nueva York, NY: W. H. Freeman and Company.

Reacciones redox

Oxidación y reducción
Algunas reacciones químicas se pueden clasificar como reacciones de reducción-oxidación o reacciones redox. La oxidación es el proceso de ...

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oxidation states in redox reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number.

Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding electrons are assigned to the more electronegative atom. An atom in its elemental form has an oxidation state of 0.

Several rules help determine oxidation states. Group I elements usually have +1, and Group II elements usually have +2. Hydrogen is typically +1, oxygen is typically -2, and halogens usually are -1. The oxidation states in a molecule or ion must add up to the total charge, so unknown values can often be found from the rest.

Carbon dioxide is a clear example. CO2 is neutral, so its total oxidation states must add to zero. Each oxygen is usually -2, so carbon must be +4 to balance the two oxygens. Another way to find oxidation numbers is to draw the Lewis structure, assign each bond to the more electronegative atom, and count electrons on each atom.

In CO2, oxygen is more electronegative than carbon, so each C=O bond is assigned to oxygen. Each oxygen gets eight electrons total, including lone pairs and bonding electrons. Oxygen has six valence electrons by default, so its oxidation number is 6 - 8 = -2. Carbon has four valence electrons by default and is assigned none, so its oxidation number is 4 - 0 = +4.

A reaction is a redox reaction when an atom’s oxidation state changes from reactants to products. To check for redox, compare oxidation states on both sides of the reaction. Many redox reactions also involve direct electron transfer between atoms or molecules. If one species gains an electron, another must lose one.

The phrase OIL-RIG helps remember the process: oxidation is losing, and reduction is gaining. The species that gains electrons is reduced, but it is also called the oxidizing agent or oxidant because it oxidizes the other species. The species that loses electrons is oxidized, but it is also called the reducing agent or reductant because it reduces the other species.

Four major reaction types often involve redox processes. In single displacement reactions, one atom replaces another atom in a compound. In combustion reactions, a compound is reduced by a strong oxidant, usually oxygen gas, and hydrocarbons or other organic compounds often produce carbon dioxide and water. In synthesis reactions, two reactants form one product. In decomposition reactions, one reactant breaks into two or more products.

Oxidation States in Redox Reactions

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An acid-base reaction is one in which a hydrogen ion, H+, is transferred from one chemical species to another. Such reactions are of central importance to ...

Reaction Stoichiometry

A balanced chemical equation provides a great deal of information in a very succinct format. Chemical formulas provide the identities of the reactants and ...

Limiting Reactant

The relative amounts of reactants and products represented in a balanced chemical equation are often referred to as stoichiometric amounts. However, in ...

Reaction Yield

The theoretical yield of a reaction is the amount of product estimated to form based on the stoichiometry of the balanced chemical equation. The ...

Stoichiometry, Product Yield, and Limiting Reactants

Chemical equations represent how a chemical reaction proceeds from reactants to products through physical or chemical change using chemical formulas.
...

CHEM.9.C

Science concepts. The student understands how matter is accounted for in chemical reactions. The student is expected to:

Oxidation States in Redox Reactions

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