Name: battery power from redox reactions
Uploaded: 2020-03-26T07:22:26.000Z
Duration: 3 min 31 s
Channel: JoVE

전기화학 반응은 두 물질 사이에서 전자가 전달되는 과정으로, 하나는 전자를 잃고 다른 하나는 전자를 얻습니다. 물질이 전자를 잃을 때, 우리는 그것이 산화를 겪었거나 산화되었다고 말합니다. 전자를 얻을 때, 우리는 그것이 환원을 겪었거나 환원되었다고 말합니다. 이 둘을 구별하는 데 도움이 되도록 'oil rig'라는 문구를 기억하십시오. 일부 전기화학 반응은 자발적으로 발생하며, 이는 갈바닉 셀에서 연구할 수 있습니다.
갈바닉 셀에는 네 가지 주요 부분이 있습니다. 첫째, 두 개의 금속 전극이 있으며 각 전극은 서로 다른 전해질 용액에 잠겨 있습니다. 용액은 각 전극에서 발생하는 반쪽 반응, 즉 산화 또는 환원 반응에 필요한 이온으로 구성됩니다. 용액은 소금 다리로 연결되어 이온의 흐름을 가능하게 하고 용액의 전하 중성을 유지합니다. 전극은 외부 회로로 연결되어 있으며, 전자는 반응 중에 이를 통해 이동합니다.
양극은 반응에서 전자를 포기하거나 산화되는 전극입니다. 음극은 전자를 얻고 감소하는 전극입니다. 이 두 레이블을 구별하는 데 도움이 되도록 음극에서 환원이 발생하므로 'red cat'이라는 문구를 기억하십시오.
그렇다면 어떤 금속이 양극 역할을 하고 어떤 금속이 음극 역할을 하는지 어떻게 알 수 있을까요? 우리는 금속의 표준 전극 전위를 사용할 수 있으며, 이는 금속이 전자를 잃는 경향을 측정한 것입니다. 음극 전위가 더 크다는 것은 금속이 전자를 잃는 경향이 더 높다는 것을 의미합니다. 전자는 항상 표준 전위가 낮은 금속에서 표준 전위가 더 큰 금속으로 흐릅니다.
갈바닉 셀에서 전자는 양극에서 음극으로 흐르므로 양극은 표준 전위가 낮은 금속이고 음극은 표준 전위가 더 높은 금속입니다. 전자가 두 전극 사이를 이동할 때 전위가 측정됩니다. 생성된 전압의 크기는 음극의 표준 전위에서 양극의 표준 전위를 뺀 값과 같습니다.
따라서 예를 들어 납 및 주석과 같이 유사한 표준 전극 전위를 가진 두 개의 금속이 갈바닉 셀에 사용되는 경우 생성되는 전압의 크기가 낮아집니다. 금속이 은과 마그네슘과 같이 다른 표준 전위를 갖는 경우 생성된 전압이 높아집니다.
이 실험실에서는 두 개의 금속 전극을 사용하여 갈바닉 셀을 구성하고 산화 및 환원 반응이 발생할 때 생성되는 전위를 측정합니다. 그런 다음 알려진 표준 전위를 사용하여 알려지지 않은 금속 전극을 식별하고 생성된 전압의 크기를 결정합니다.

갈바닉 셀

Galvanic Cells

전기화학
전기화학은 전기 에너지와 화학적 변화 사이의 관계를 연구하는 화학의 한 분야입니다. 이러한 화학 반응은 한 종에서 다른 종으로 전자의 이동을 포함합니다. 이 움직임은 전류를 생성하거나 적용된 전류에 의해 구동됩니다.
전기화학의 핵심 반응은 산화 환원 또는 산화 환원 반응입니다. 산화 환원 반응은 두 개의 반쪽 반응으로 구성됩니다. 물질이 전자를 잃는 산화 반응과 물질이 전자를 얻는 환원 반응. 이 화학 반응으로 인해 각 물질이 산화 상태가 변합니다.
전자를 잃거나 산화되는 원자 또는 분자가 환원제입니다. 전자를 받아들이거나 환원되는 원자 또는 분자는 산화제입니다. 이러한 관계를 기억하는 한 가지 방법은 '석유 굴착 장치'라는 문구를 사용하는 것인데, 이는 'oxidation is losing – reduction is gaining'을 의미합니다.
<h4>전기화학 전지</h4>
전기화학 전지는 산화 환원 반응에서 방출된 에너지에서 전류를 생성하는 장치입니다. 전기화학 셀은 반응 챔버 또는 챔버와 두 개의 전도성 전극(양극과 음극)으로 구성됩니다. 양극과 음극은 전기적으로 연결되어 있으며 반응 챔버는 전해질로 채워져 있습니다. 두 챔버 사이에는 회로를 완성하고 이온이 전극 사이를 이동할 수 있도록 하는 소금 다리가 있습니다.
환원은 음극에서 발생하고 산화는 양극에서 발생합니다. 이것은 니모닉 "빨간 고양이"를 사용하여 쉽게 기억할 수 있는데, 이는 고양이호드에서 붉은uction이 발생한다는 것을 의미합니다.
전기화학 전지에는 두 가지 유형이 있습니다. 하나는 전기 에너지를 사용하여 비자발적 반응을 일으키는 전해 전지입니다. 이러한 유형의 셀에서는 외부 전원에서 전기 에너지가 공급됩니다. 다른 유형의 전지는 전기 에너지를 생성하기 위해 자발적 반응을 사용하는 갈바닉 전지입니다. 배터리는 갈바닉 셀의 예입니다.
<h4>갈바닉 셀</h4>
볼타 전지라고도 하는 갈바닉 전지는 두 개의 반쪽 전지로 구성됩니다. 각 반쪽 셀에는 전해질에 잠긴 금속 전극이 포함되어 있습니다. 외부 회로는 두 전극을 연결하고 염교는 두 전해질 용액을 연결합니다. 전자는 양극에서 음극으로 흐릅니다. 산화 반쪽 반응은 양극에서 일어나고 환원 반쪽 반응은 음극에서 발생합니다. 예를 들어, 구리와 마그네슘 사이의 갈바닉 셀에서는 음극에서 다음과 같은 반쪽 반응이 발생합니다.
Cu2+ + 2e- → Cu
그리고 다음과 같은 반쪽 반응이 양극에서 발생합니다.
Mg → Mg2+ + 2e-
전자는 양극에서 산화되는 동안 손실되기 때문에 외부 회로를 통해 이동하여 음극을 줄여 전류를 생성합니다.
양극이 산화됨에 따라 전해질에서 양이온의 농도가 증가합니다. 마찬가지로, 음극이 감소함에 따라 전해질에서 음이온의 농도가 증가합니다. 전기 중립성을 유지하기 위해 이온은 소금 다리를 가로질러 이동합니다. 양극에서 양이온이 생성되면 음이온은 염교를 사용하여 양극 측의 용액에서 이동합니다. 음극 측에서는 음이온이 생성되어 양이온이 소금 다리에서 음극 측의 용액으로 이동하도록 유도합니다. 전자는 외부 회로 와이어를 통해 이동하고 이온은 소금 다리와 용액을 통해 흐른다는 것을 기억하는 것이 중요합니다.
<h4>저감 가능성</h4>
일부 금속은 다른 금속보다 전자를 잃는 경향이 더 큽니다. 따라서 갈바닉 셀에서 생성되는 전류의 크기는 금속 전극의 유형에 따라 다릅니다. 물질의 표준 전극 전위(Eo)는 물질이 전자를 잃는 경향을 측정한 것입니다. 전극 전위가 거의 동일한 두 개의 금속을 사용하면 생성되는 전류의 크기가 작아집니다. 전극 전위가 매우 다른 두 개의 금속을 사용하면 전류의 크기가 커집니다. 환원 전위가 클수록 금속이 환원되어 산화제로 작용할 가능성이 높아집니다.
구리-마그네슘 갈바닉 셀로 돌아가서 구리의 표준 전극 전위는 0.337볼트이고 마그네슘의 표준 전극 전위는 -2.370볼트입니다. 이 예에서 구리는 음극이고 마그네슘은 양극입니다.
갈바닉 전지 실험을 수행할 때 멀티미터를 사용하여 두 전극 간의 전위차를 모니터링합니다. 측정된 전압은 두 반쪽 반응 사이의 전위 차이와 같습니다.
ΔEº = Eº음극 - Eº양극
표준 전극 전위는 두 반쪽 전지가 모두 1M, 1bar 및 298.15K(25°C)의 표준 조건에 있다고 가정합니다. 전압은 전해질 용액의 농도에 따라 달라지며, 이는 Nernst 방정식을 사용하여 결정할 수 있습니다.
<img src="/CDNSource/lm/labs/52/52_Concepts_4.jpg">
여기서, E는 전위차 또는 측정된 전압에 해당하고, E는 표준 환원 전위, R은 범용 기체 상수(8.314462618 J/mol·K), T는 켈빈 단위로 측정된 온도, F는 패러데이 상수(96,485.33212 C⋅mol-1), n은 반응에서 전달된 전자의 수, Qh는 반응 지수입니다. 반응 지수는 평형 상수에 해당하는 전기화학적 등가물입니다.
<h4>참조</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). 화학 및 화학 반응성. 캘리포니아 벨몬트 : Brooks / Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). 화학: 물질과 변화의 분자적 성질. 매사추세츠주 보스턴: 맥그로 힐.</li>
	<li style="font-size:17px">Harris, D.C. (2015). 정량적 화학 분석. 6차 개정판. 뉴욕, 뉴욕 : WH 프리먼 앤 컴퍼니.</li>
</ol>

전기화학
전기화학은 전기 에너지와 화학적 변화 사이의 관계를 연구하는 화학의 한 분야입니다. 이러한 화학 물질은 ...

Education

교육

JoVE Lab Manual

Chemistry

화학

battery power from redox reactions

Electrochemistry studies how chemical change and electrical energy are linked. In this branch of chemistry, electrons move from one species to another. That movement can either produce current or be driven by an applied current. The main reaction in electrochemistry is the oxidation-reduction, or redox, reaction. A redox reaction has two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. These changes also shift the oxidation state of each substance. The species that loses electrons is the reducing agent, and the species that gains electrons is the oxidizing agent. A common memory aid is “oil-rig,” which means oxidation is losing and reduction is gaining.

An electrochemical cell is a device that turns the energy from a redox reaction into electric current. It includes reaction chamber or chambers and two conductive electrodes, an anode and a cathode. The electrodes are connected electrically, and the chamber contains an electrolyte. A salt bridge sits between the two chambers. It completes the circuit and lets ions move between the electrodes. Reduction occurs at the cathode, and oxidation occurs at the anode. Students often remember this with “red cat,” which means reduction occurs at the cathode. The two main kinds of electrochemical cells are electrolytic cells and galvanic cells. An electrolytic cell uses external electrical energy to drive a nonspontaneous reaction. A galvanic cell uses a spontaneous reaction to generate electrical energy. Batteries are examples of galvanic cells.

Galvanic cells, also called voltaic cells, have two half-cells. Each half-cell contains a metal electrode immersed in an electrolyte. An external circuit connects the electrodes, and a salt bridge connects the two electrolyte solutions. Electrons flow from the anode to the cathode. Oxidation happens at the anode, and reduction happens at the cathode. In a copper-magnesium galvanic cell, copper is reduced at the cathode through the half-reaction Cu2+ + 2e- → Cu. Magnesium is oxidized at the anode through the half-reaction Mg → Mg2+ + 2e-. As electrons move through the external circuit, they reduce the cathode and generate current. As the anode is oxidized, the concentration of cations increases in that electrolyte. As the cathode is reduced, the concentration of anions increases in that electrolyte.

The salt bridge keeps the cell electrically neutral. When cations are created at the anode, anions move from the anode side through the salt bridge. On the cathode side, anions are created, so cations move from the salt bridge into that solution. It is important to separate electron flow from ion flow. Electrons travel through the external wires. Ions move through the salt bridge and the solutions.

Some metals lose electrons more easily than others. For that reason, the current produced by a galvanic cell depends on the metals used for the electrodes. The standard electrode potential, E°, measures this tendency. If two metals have nearly equal electrode potentials, the current is small. If their electrode potentials are very different, the current is larger. A larger reduction potential means a metal is more likely to be reduced and act as the oxidizing agent. In the copper-magnesium cell, copper has a standard electrode potential of 0.337 volts, and magnesium has a standard electrode potential of -2.370 volts. That is why copper is the cathode and magnesium is the anode.

In a galvanic cell experiment, a multimeter is used to measure the potential difference between the two electrodes. The measured voltage equals the difference between the two half-reactions, written as ΔE° = E° cathode - E° anode. Standard electrode potential assumes standard conditions of 1 M, 1 bar, and 298.15 K, or 25 °C. The voltage also depends on electrolyte concentration. That dependence can be found with the Nernst equation. In the equation, E is the measured potential difference, E° is the standard reduction potential, R is the universal gas constant, T is temperature in Kelvin, F is Faraday’s constant, n is the number of electrons transferred, and Qh is the reaction quotient. The reaction quotient is the electrochemical equivalent of the equilibrium constant.

Battery Power from Redox Reactions

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electrolytic cells

Electroplating with Electrolytic Cells

Electrochemistry links electrical energy with chemical change, and electrolytic cells show how electricity can drive a nonspontaneous reaction. In these reactions, electrons move from one species to another. The key chemistry is a redox reaction, or oxidation-reduction reaction, which happens in two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. The substance that loses electrons is the reducing agent, and the substance that gains electrons is the...

proper lab notebook keeping

Recording a Reproducible Lab Experiment

Accurate lab notebook records are essential in science and organic chemistry labs. Without clear notes, descriptions, quantities, and observations, an experiment cannot be repeated or checked. Good record keeping supports reproducibility, which means other people can follow the same work and get similar results. A laboratory notebook is useful in school labs, research settings, and industry. It can also become a legal record when an idea, process, substance, or technique is patented and...

basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

Organic chemistry labs use specific glassware, careful weighing steps, and controlled heating to keep reactions safe and accurate. Beakers and Erlenmeyer flasks are often used for mixing or holding solvents, but they are not meant for measuring volume unless only an approximate amount is needed. Volumetric glassware is used when a precise volume matters. This group includes graduated cylinders, volumetric pipettes, and volumetric flasks. A graduated cylinder is commonly used in the organic lab...

melting points

How Impurities Change Melting Points

Melting point helps identify an organic compound by showing the temperature where a solid turns into a liquid at 1 atmosphere of pressure. It is a physical property, like solubility, density, color, and electronegativity. Because the exact start of melting is hard to measure, the result is reported as a range. The lower end is when the first drops of liquid appear. The upper end is when the last solid has melted. Scientists compare this range with literature values to help identify a compound. <br...

boiling points

Boiling Point and Vapor Pressure

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value. Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas...

recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

chemistry

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Battery Power from Redox Reactions

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