Name: galvanic cells and battery reactions
Uploaded: 2020-09-24T15:06:52.000Z
Duration: 2 min 47 s
Channel: JoVE

自发的氧化还原反应会产生电能，可以为电气设备供电。但它是如何工作的呢？请考虑铜和硝酸银溶液 之间的氧化还原反应。当放在一个容器中时，铜 被氧化成亚铜离子，而银离子 被还原成银沉淀。这里，电子转移是直接的，不产生电流。然而，当这些半反应 在物理上被隔开，并通过 外部电路连接时，就会观察到电流。这种装置称为电化学电池，进一步 定义为自发氧化还原反应的原电池 或伏打电池。原电池由两个半电池组成，在其相应的电解质溶液中包含固体金属电极 的半电池反应混合物。这里指的是硝酸铜水溶液中的铜 和硝酸银水溶液中的银。被隔开的反应物具有电池电势，但由于没有外部连接，不会发生反应或产生电子流。一旦与外部连接，电子将被迫间接流过外部电路，从而使反应在各自的电极上发生。按照惯例，氧化反应发生在带负电荷的 阳极，还原反应发生在带正电荷的 阴极。随着电子的转移，在氧化半电池中形成正离子，在还原半电池中形成负离子。这会导致正电荷和负电荷的积聚，阻止电子进一步流动，必须 不断中和才能使反应持续进行。因此，两个半电池通过一个 盐桥连接：一个倒置的 U 形管，里面装有惰性电解质的糊状或凝胶状物质，比如硝酸钠。随着氧化还原反应的进行，反离子流入各自的半电池中，来确保电荷中和，而不会混合电解质。这是用来描述原电池的 特殊符号或电池示意图。左边是氧化反应，右边是还原反应。垂直双线表示连接两个半电池的盐桥，垂直单线表示 组分相之间的界面。如果同一相中存在两个或多个组分，则用逗号分隔。

伏打/ 伽凡尼电池

Voltaic/Galvanic Cells

自发化学反应 
 自发的氧化还原反应在性质上非常强烈。 为遥控器供电的一次性 AA 电池中发生的化学反应就是自发氧化还原反应的一个例子。 另一个示例是将卷绕铜线浸入一个水性银硝酸盐溶液中。 反应表明，颜色从无色变为明亮的蓝色，并在铜线上形成灰色沉淀物，色彩逐渐，视觉上令人印象深刻。 在这项实验中，铜会被氧化以形成铜质离子，从而使溶液呈蓝色，而银色离子则会被还原为在电线上形成银沉淀。 
 这种反应可以归纳如下： 
 <img alt="Eq1" src="/files/ftp_upload/11434/11434_Equation_1.png" style="text-align: center; height: 105px;" />
 在这里，电子从铜线直接和自发地转移到水化银离子。 
 电化学细胞和原电池（伽凡尼电池） 
 假设设备包含氧化还原系统的所有反应物和生成物，但阻止反应物之间的物理接触。 因此，电子的直接传输是被阻止的；相反，它是通过与分离的反应物相接触的外部电路间接发生的。 这类装置通常称为电化学细胞。 
 电化学电池是一种仪器，在该仪器中，氧化还原反应产生电流，而反应原子之间不会直接接触。 因自发氧化还原反应而产生电流的电化学细胞称为电镀或伏打电池 (以 Luigi Galvani 和 Alessandro Volta 命名)。 
 原电池（伽凡尼电池）的组件 
 图 1 所示为基于铜和银 (i) 之间自发反应的原电池（伽凡尼电池）。 典型的原电池（伽凡尼电池）由两个半电池组成，每个共轭都包含一个氧化还原反应物对或一对单个。 左侧的半电池包含铜 (0) /Cu (II) 对数，形式为实心铜箔和硝酸铜水溶液。 右侧半电池包含 Ag (i) /Ag (0) 对数作为固体银箔和水化银硝酸盐溶液。 外部电路通过其实心箔连接到每个半电池，这意味着 Cu 和 Ag 箔各自充当电极。 反应发生在每个半电池反应混合物及其相应电极之间的接口处。 阳极是发生氧化的电极，它具有负电荷，而阴极是发生还原的电极，它具有正电荷。 
 这两个半电池通过盐桥连接，盐桥是一个倒 U 形管，其中含有一种凝胶或惰性电解质的糊状物，如氯化钾或硝酸铵。 盐桥有助于使反应混合物保持分离，同时确保反应的电荷平衡。 该细胞中的自发反应会在阳极半电池中产生 Cu2+ 阳离子，并在阴极半电池中消耗 AA+ 离子，从而产生来自盐桥的惰性离子补偿性流动，从而保持电荷平衡。 盐桥提供惰性离子的流动，确保通过中和阳极和阴极处的正负离子的积聚来继续反应。 因此，阳极半电池中 Cu2+ 浓度的增加是由盐桥流入 NO3− 来平衡的，而 Na+ 流入阴极半电池的流量补偿了 AA+ 浓度的下降。 
 <img alt="Image1" src="/files/ftp_upload/11434/11434_Image1.png" style="text-align: center; height: 350px;" />
 图 1 ：基于铜离子和银离子之间自发反应的原电池（伽凡尼电池）。 
 使用电池示意图或电池符号表示原电池（伽凡尼电池）。 
 使用电池示意图或电池符号象征性地表示原电池（伽凡尼电池）。 
 • 在电池示意图中，组件相位之间的所有接口都由垂直平行线表示。 
 •  如果两个或多个组件在同一阶段存在，它们将以逗号分隔。 
 •  阳极在原理图的左侧表示，阴极在右侧表示。 
 •  双垂直线表示两个半反应之间的盐桥或多孔分区。 
 •  根据惯例，原理图以阳极开始，从左到右依次识别单元内遇到的相位和接口，最后是阴极。 
 例如，上述原电池（伽凡尼电池）由一个实心铜阳极组成，该阳极浸入通过盐桥连接到一个水银 (i) 硝酸盐溶液，其中是实心银阴极。 按照上述准则将此语句转换为符号，将生成单元格原理图： 
 <img alt="Eq2" src="/files/ftp_upload/11434/11434_Equation_2.png" style="text-align: center; height: 48px;" />
 本文改编自<a href="https://openstax.org/books/chemistry-2e/pages/17-2-galvanic-cells"> Openstax, 化学 2e,</a><a href="https://openstax.org/books/chemistry-2e/pages/17-2-galvanic-cells"></a><a href="https://openstax.org/books/chemistry-2e/pages/17-2-galvanic-cells"> 第17.2节：原电池（伽凡尼电池）。 </a>

自发化学反应  
自发的氧化还原反应在自然界中广泛存在。在为一次性AA电池供电的化学反应中……

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KEY TERMS AND CONCEPTS

关键术语与概念

galvanic cells and battery reactions

Galvanic cells use spontaneous redox reactions to produce electric current. A common example is a disposable AA battery, which powers devices by turning chemical energy into electrical energy. Another example is a copper wire placed in silver nitrate solution, where the solution slowly turns bright blue and a grey solid forms on the wire.

In the copper and silver reaction, copper is oxidized and silver ions are reduced. Copper forms cuprous ions, which give the solution its blue color. At the same time, silver ions gain electrons and become silver metal on the copper wire. This is a direct, spontaneous transfer of electrons from copper to the aqueous silver ions.

An electrochemical cell keeps the reactants and products of a redox reaction in the same device but prevents the reacting atoms from touching. Because of this separation, electrons move indirectly through an external circuit instead of moving by direct contact. When the current comes from a spontaneous redox reaction, the cell is called a galvanic cell or a voltaic cell. These names come from Luigi Galvani and Alessandro Volta.

A galvanic cell has two half-cells, and each half-cell contains one redox couple. In the copper-silver cell, the left half-cell contains the Cu(0)/Cu(II) couple as solid copper foil in copper nitrate solution. The right half-cell contains the Ag(I)/Ag(0) couple as solid silver foil in silver nitrate solution. Each metal foil is an electrode because the external circuit connects to it.

The reaction happens at the boundary between each solution and its electrode. Oxidation occurs at the anode, which carries a negative charge. Reduction occurs at the cathode, which carries a positive charge. The two half-cells are joined by a salt bridge, an inverted U-tube with a gel or paste of an inert electrolyte such as potassium chloride or ammonium nitrate.

The salt bridge keeps the half-reactions separate and helps maintain charge balance. As copper ions build up in the anode half-cell, inert nitrate ions move in to balance the charge. At the cathode, silver ions are used up, so inert sodium ions can move in to compensate. This ion flow helps the cell keep running.

A galvanic cell can also be written as a cell notation, or cell schematic. Vertical lines show phase boundaries, and a double line shows the salt bridge or a porous partition. By convention, the anode is written on the left and the cathode on the right. The notation starts with the anode and moves left to right through each phase and interface until it ends at the cathode, such as in the copper-silver cell described here.

Galvanic Cells and Battery Reactions

balancing redox equations

Redox Reactions and Half-Reaction Balancing

Redox reactions involve electron transfer and changes in oxidation number. In electrochemistry, these reactions connect chemical changes with electrical energy. They also power technologies such as industrial metal processing and rechargeable batteries used in electric vehicles. Oxidation number is a way to track how an atom's electronic environment changes compared with the pure element, where the oxidation number is zero. For a simple ionic compound, the oxidation number matches the ion...

electromotive force

Cell Voltage and Electron Flow

Electric current is the flow of electric charge through a conducting medium or a solution. In wires, that charge is carried by electrons. In some solutions, ions can also move and carry charge. When electrons move through a wire, they produce an electric current. This idea connects to redox reactions, where electrons are lost and gained. In the spontaneous reaction between zinc and copper ions, zinc is oxidized to zinc ions. Copper ions are reduced to solid copper. Even so, this direct...

voltaic/galvanic cells

Galvanic cells use spontaneous redox reactions to produce electric current. A common example is a disposable AA battery, which powers devices by turning chemical energy into electrical energy. Another example is a copper wire placed in silver nitrate solution, where the solution slowly turns bright blue and a grey solid forms on the wire. In the copper and silver reaction, copper is oxidized and silver ions are reduced. Copper forms cuprous ions, which give the solution its blue color. At the...

standard electrode potentials

Using Electrode Potentials to Predict Reactions

Electrode potentials help predict whether a redox reaction will happen on its own. A redox reaction involves electron transfer. In electrochemistry, the measured value is called cell potential or cell voltage. It shows the energy linked to charge transfer and is measured in volts, where 1 volt equals 1 joule per coulomb. A single half-cell cannot be measured by itself because electron transfer needs both a donor and a receiver. For that reason, scientists measure the difference between two...

cell potential and free energy

Redox Cell Potential, ΔG°, and K

Redox cell potential connects chemical energy, free energy change, and the equilibrium constant in an electrochemical cell. In these reactions, chemical energy is converted into electrical energy. That link helps predict whether a reaction is spontaneous and how far it may proceed. Thermodynamics is the study of how heat and other forms of energy are related. In an electrochemical cell, cell potential can also reflect oxidizing strength or reducing strength. A similar idea appears in acid-base...

the nernst equation

Cell Potential Under Changing Conditions

Cell potential changes when a redox reaction does not run at standard conditions. Standard cell potentials connect with standard free energy change, ΔG°, and the equilibrium constant K, but those relationships only hold at 1 M concentration, 298 K, and 1 atmosphere. A zinc(II) and tin(II) redox cell with E°cell = +0.291 V and ΔG° = −56.2 kJ is spontaneous under those standard conditions. As a cell discharges, the reactant concentration changes and the cell potential steadily drops. Many redox...

concentration cells

Cell Potential from Concentration Differences

Concentration cells are voltaic cells that use two almost identical half-cells. The half-cells use the same electrode and the same half-reaction. They differ only in the concentration of one redox species, so the cell potential depends on that concentration difference. In a concentration cell, the Nernst equation can be used to find the cell potential. For the zinc example shown, the calculated cell potential is positive. A positive cell potential means the overall reaction is spontaneous. <br...

batteries and fuel cells

Primary, Rechargeable Batteries and Fuel Cells

Batteries and fuel cells are galvanic cells that supply electrical power for many applications. They range from tiny button batteries in wristwatches to large systems that can provide backup energy to municipal power grids. Some are primary cells, which are single-use and cannot be recharged. Others are secondary cells, which use reversible reactions and can be charged again by an external power source. A common primary battery is the dry cell. It uses zinc as both the container and the anode,...

corrosion

Rusting and Metal Protection

Corrosion is the natural breakdown of metals through electrochemical reactions. It can appear as rust on iron, tarnish on silver, or a blue-green patina on copper. In each case, the metal is oxidized. Some corrosion products can protect the surface, while others keep damaging the metal. Rusting is the harmful type of corrosion seen in iron. It happens when iron is exposed to oxygen and water. A galvanic cell forms on the iron surface, and this drives oxidation at the anodic region and...

electrolysis

Electrolysis in Batteries and Metal Production

Electrolysis uses electrical energy to drive a nonspontaneous redox reaction. In a galvanic cell, a spontaneous redox reaction does electrical work on the surroundings by sending electrons through an external circuit. In electrolysis, an external circuit does work on the redox system by applying a voltage large enough to force the reaction in the opposite direction. This process is used in several real-world settings. Recharging a battery is one example, because an outside power source drives...

key terms and concepts

Explore how galvanic cells turn spontaneous redox reactions into electric current, using battery chemistry, half-cells, electrodes, salt bridges, and cell notation.

Galvanic Cells and Battery Reactions | JoVE K12

chemistry

JoVE Core 化学通过简单明了且通俗易懂的动画视频课程，将普通化学概念带入到现实生活当中。此外，在科学家行动视频中，我们演示了在实验室中进行的经典和原始研究实验。

Galvanic Cells and Battery Reactions

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