Name: electron transfer in redox
Uploaded: 2019-03-11T09:21:00.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Systems

ESS.EES.3.1

Redox Reactions

- [Istruttore] Durante la
riduzione dell'ossidazione,

o le reazioni di ossidoriduzione,

gli elettroni vengono
trasferiti tra gli atomi.

La molecola che dona un
elettrone viene ossidata,

e la molecola che riceve
un elettrone viene ridotta.

Ha una carica meno positiva.

Per esempio, quando gli atomi
neutrali di sodio e cloro

diventano ioni, il sodio perde
un elettrone, viene ossidato,

e il cloro guadagna un
elettrone, venendo così ridotto.

Inoltre, la molecola che dona un elettrone

è chiamato agente riducente,

mentre la molecola che riceve l'elettrone

è l'agente di ossidazione.

Di nuovo, il sodio è ossidato,
quindi è l'agente riducente,

e il cloro è ridotto,
quindi è l'agente ossidante.

Flowers, P., Theopold, K., Langley, R., Robinson, W. R., Clark, M. A., Douglas, M., Choi, J. Sezione 4.2: Classificazione delle reazioni chimiche. In Chimica 2e. OpenStax. Houston, Texas (2019).

reazioni di ossidoriduzione

Le reazioni di riduzione dell'ossidazione, o redox, modificano gli stati di ossidazione degli atomi attraverso il trasferimento di elettroni da un atomo, l'agente di riduzione, ad un altro atomo che riceve l'elettrone, l'agente ossidante. Qui, l'atomo che dona elettroni viene ossidato, perde gli elettroni, e l'atomo che accetta gli elettroni si riduce, ha una carica meno positiva perché guadagna elettroni. Il movimento dell'energia nelle reazioni redox dipende dal potenziale degli atomi di attirare elettroni leganti, la loro elettronegatività. Se l'agente ossidante è più elettronegativo dell'agente depuratore, l'energia viene rilasciata. Tuttavia, se l'agente ossidante è meno elettronegativo dell'agente di riduzione, è necessario l'input di energia.

<h4>Riduzione degli agenti otteneti</h4>

L'ossidazione è una perdita o un guadagno di elettroni? La terminologia può confondere. L'acronimo OIL RIG è comunemente usato per ricordare. Sta per ossidazione è la perdita; riduzione è guadagno. Quindi, se un atomo viene ossidato, allora perde gli elettroni. Come agente di riduzione, l'atomo ossidato trasferisce gli elettroni ad un altro atomo, causandone la riduzione. Con OIL RIG in mente, la maggior parte delle domande sui membri di una reazione redox può essere risolta.

<h4>Elettronegatività ed Energia</h4>

Le reazioni di Redox producono o richiedono energia. Se un atomo perde un elettrone per un atomo più elettronegativo, allora è una reazione energeticamente favorevole e l'energia viene rilasciata. Questo è in realtà molto logico, simile a un uomo forte che vince un tiro alla fune con un uomo più debole, perché un atomo più elettronegativo ha una maggiore capacità di tirare gli elettroni a se stesso. Un esempio biologico di questo tipo di reazione è la respirazione cellulare, in cui l'energia viene rilasciata e utilizzata per creare ATP, una forma di energia che le cellule possono facilmente utilizzare.

Altre reazioni redox richiedono, piuttosto che rilasciare, energia. Se un elettrone passa da un atomo più elettronegativo a un atomo meno elettronegativo, deve essere utilizzata l'energia. Questo è come un uomo più debole che vince il tiro alla fune con un uomo più forte: richiede energia da una fonte esterna. Un esempio biologico è la fotosintesi, in cui gli elettroni vengono trasferiti dall'acqua all'anidride carbonica con l'aiuto dell'energia sotto forma di luce.

<h4>Trasferimento incompleto di elettroni</h4>

Una reazione redox può verificarsi non solo quando un elettrone viene trasferito, ma anche quando c'è un cambiamento nella condivisione di un elettrone in un legame covalente! Ad esempio, quando il metano e l'ossigeno reagiscono, producono anidride carbonica e acqua. In questo caso, il carbonio nel metano viene ossidato. Questo perché gli elettroni nel metano sono equamente condivisi tra carbonio e idrogeno, mentre il carbonio nell'anidride carbonica è parzialmente positivo poiché l'ossigeno attira gli elettroni più del carbonio.

Reazioni di ossidoriduzione

Oxidation-reduction or redox reactions involve the transfer of electrons from one molecule or atom to another. When an atom gains an electron, another ...

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KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

electron transfer in redox

Redox reactions are chemical reactions that involve electron transfer between atoms or molecules. When one particle gains electrons, another must lose them at the same time. That is why oxidation and reduction always happen together.

The two roles in a redox reaction are linked. The atom that is oxidized acts as the reducing agent, or reductant. The atom that is reduced acts as the oxidizing agent, or oxidant. A simple way to remember the ideas is OIL-RIG, which means oxidation is losing electrons and reduction is gaining electrons.

Redox reactions also change oxidation states, or oxidation numbers. An oxidation state is the charge an atom would have if all of its bonds were purely ionic. Checking whether oxidation numbers change in the reactants can help identify a redox reaction.

A sodium and chlorine reaction makes this idea clear. Sodium is oxidized, and chlorine is reduced to form sodium chloride. The process can be shown with half-reactions, which separate the fate of each reactant. In these equations, sodium goes from an oxidation number of 0 to 1+, while chlorine in Cl2 goes from 0 to 1-.

Electron transfer is not always complete. A redox reaction can also happen when the sharing of electrons changes in a covalent bond. Methane and oxygen can react to form carbon dioxide and water. In methane, electrons are shared equally between carbon and hydrogen, but in carbon dioxide the carbon is partially positive because oxygen pulls electrons more strongly. In that reaction, carbon dioxide is oxidized and oxygen is reduced.

Electron Transfer in Redox

the periodic table and organismal elements

the-periodic-table-and-organismal-elements

Periodic Table Basics for Living Things

The periodic table helps explain which elements living things need and how those elements are related. Elements are the smallest units of matter that cannot be broken down further by chemical processes. There are 118 known elements, but not all occur naturally, and even fewer are essential for life. Living matter is made mostly of carbon, nitrogen, hydrogen, and oxygen. Together, these elements make up most of the human body and are also found in all life on Earth. Smaller amounts of calcium,...

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covalent bonds

Electronegativity and Covalent Bond Polarity

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ionic bonds

Ionic Compounds and Electrolytes

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hydrogen bonds

Hydrogen Bonds in Water

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van der waals interactions

Intermolecular Forces in Polar Solutions

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Elements, Compounds, and Bonding

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redox reactions

Redox reactions are chemical reactions that involve electron transfer between atoms or molecules. When one particle gains electrons, another must lose them at the same time. That is why oxidation and reduction always happen together. The two roles in a redox reaction are linked. The atom that is oxidized acts as the reducing agent, or reductant. The atom that is reduced acts as the oxidizing agent, or oxidant. A simple way to remember the ideas is OIL-RIG, which means oxidation is losing...

cohesion

Water Molecules and Surface Tension

Water molecules stick to each other through cohesion. Water is neutral overall, but it is a polar molecule. The oxygen atom in one water molecule has a partial negative charge, and it can bind with a hydrogen atom that has a partial positive charge in another water molecule. This forms a hydrogen bond. Each water molecule can form up to four hydrogen bonds with other water molecules, and these bonds give water its cohesive nature. Cohesion helps water form droplets on a surface. Water does not...

adhesion

Water Climbing by Adhesion

Water can climb or stick to surfaces because of adhesion, which is the attraction between different kinds of molecules. In water, this is easy to see on polar surfaces such as glass or cellulose in plants. The positive hydrogen side of water is more attracted to the negative oxygen in silica than to nearby water molecules. This attraction helps explain capillary action. If a narrow glass tube is placed in a beaker of water, water molecules attach to the tube’s surface and the water level rises.

states of water

Water Phase Changes and Ice Density

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specific heat

How Specific Heat Affects Temperature

Specific heat capacity describes how much energy a substance needs to rise by 1 degree Celsius for each gram. It is often written with calories, grams, and degrees Celsius, but it can also be shown in joules, kilograms, and Kelvin. For water, 1 gram needs 1 calorie to increase by 1°C, which is also written as 1 cal/g-°C or 4186 J/kg/K. Water has a high specific heat capacity, so it takes in a large amount of heat before its temperature changes much. It also gives off a lot of heat when it...

vaporization

Vaporization, Boiling, and Evaporation

Vaporization changes a liquid into vapor when temperature adds enough kinetic energy to overcome intermolecular forces. It is a surface phenomenon, which means it starts at the liquid’s surface. The energy needed to vaporize a set amount of liquid at a given pressure and constant temperature is called the heat of vaporization. Water shows this process clearly. When liquid water is vaporized, it becomes steam. One way this happens is boiling, which occurs when vapor bubbles form beneath the...

solvents

Water as a Biological Solvent

Water acts as a biological solvent in many living systems. A solvent is a substance, usually a liquid, that dissolves another substance called a solute. When a solvent and a solute mix, they form a solution, which is a uniform mixture of both parts. Water is called a universal biological solvent because its polar structure helps it dissolve many other polar compounds. Polarity means that one side of the molecule has a slight positive charge and the other side has a slight negative charge.

carbon skeletons

Carbon Backbones in Biomolecules

Carbon backbones give biological molecules their structure and flexibility. Living things are built from macromolecules that contain carbon atoms, and organic compounds are defined by a carbon backbone. Carbon is tetravalent, so each carbon atom can bond with four other atoms. Its valence electrons are stable, so carbon rarely becomes an ion. As carbon chains get longer, they can form ring structures, double bonds, and branching side chains. Carbon-carbon bonds create the carbon skeleton.

key terms and concepts

Learn how redox reactions move electrons, change oxidation states, and use half-reactions to track sodium, chlorine, methane, and oxygen.

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Electron Transfer in Redox

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