Difference Between Galvanic Cell And Electrolytic Cell

Dua jenis sel elektrokimia yang paling umum adalah sel galvanik dan sel elektrolitik, masing-masing memanfaatkan reaksi redoks untuk menghasilkan atau mengonsumsi energi listrik. Meskipun keduanya melibatkan elektroda dan elektrolit, prinsip kerja dan aplikasinya sangat berbeda. Memahami perbedaan antara keduanya sangat penting dalam bidang kimia, ilmu material, dan berbagai aplikasi industri.

Galvanic Cell vs. Electrolytic Cell: Unveiling the Electrochemical Dichotomy

Sel galvanik, juga dikenal sebagai sel volta, memanfaatkan reaksi redoks spontan untuk menghasilkan energi listrik. Sebaliknya, sel elektrolitik menggunakan energi listrik untuk mendorong reaksi redoks non-spontan. Perbedaan mendasar ini menghasilkan perbedaan signifikan dalam desain, fungsi, dan aplikasi kedua jenis sel ini.

Fundamental Principles

• Galvanic Cells: These cells convert chemical energy into electrical energy. They operate based on the principle of spontaneous redox reactions, where electrons are transferred from one species to another through an external circuit.
• Electrolytic Cells: These cells convert electrical energy into chemical energy. They utilize an external source of electrical energy to drive non-spontaneous redox reactions, forcing electrons to flow in a direction that would not occur naturally.

Key Differentiating Factors

Anatomy of a Galvanic Cell

Sebuah sel galvanik biasanya terdiri dari dua setengah sel, masing-masing berisi elektroda yang terendam dalam larutan elektrolit. Kedua setengah sel dihubungkan oleh jembatan garam atau membran berpori, yang memungkinkan ion bermigrasi untuk mempertahankan netralitas listrik.

• Electrodes: The electrodes are conductive materials (typically metals) where oxidation and reduction reactions occur.
  • Anode: The electrode where oxidation occurs (loss of electrons). In a galvanic cell, the anode is negatively charged as it releases electrons.
  • Cathode: The electrode where reduction occurs (gain of electrons). In a galvanic cell, the cathode is positively charged as it receives electrons.
• Electrolyte: The electrolyte is a solution containing ions that can conduct electricity. The electrolyte in each half-cell must contain ions of the same metal as the electrode.
• Salt Bridge/Porous Membrane: The salt bridge or porous membrane connects the two half-cells and allows ions to flow between them, maintaining electrical neutrality. This prevents the buildup of charge in either half-cell, which would stop the reaction.

Anatomy of an Electrolytic Cell

Sebuah sel elektrolitik juga terdiri dari dua elektroda yang terendam dalam larutan elektrolit, tetapi tidak seperti sel galvanik, sel tersebut memerlukan sumber energi listrik eksternal, seperti baterai atau catu daya, untuk mendorong reaksi non-spontan.

• Electrodes: Similar to galvanic cells, electrolytic cells also have two electrodes:
  • Anode: The electrode where oxidation occurs (loss of electrons). In an electrolytic cell, the anode is positively charged as it is connected to the positive terminal of the external power source.
  • Cathode: The electrode where reduction occurs (gain of electrons). In an electrolytic cell, the cathode is negatively charged as it is connected to the negative terminal of the external power source.
• Electrolyte: The electrolyte is a solution containing ions that will be oxidized and reduced.
• External Power Source: An external power source (e.g., battery) is required to provide the electrical energy needed to drive the non-spontaneous reaction.

The Nernst Equation: Quantifying Cell Potential

Persamaan Nernst menghubungkan potensial sel dari sel elektrokimia dengan kondisi standar, suhu, dan konsentrasi reaktan dan produk. Ini memungkinkan kita untuk menghitung potensial sel di bawah kondisi non-standar.

The Nernst equation is expressed as:

E = E° - (RT/nF) * ln(Q)

where:

• E = Cell potential under non-standard conditions
• E° = Cell potential under standard conditions
• R = Ideal gas constant (8.314 J/(mol·K))
• T = Temperature in Kelvin
• n = Number of moles of electrons transferred in the balanced redox reaction
• F = Faraday's constant (96485 C/mol)
• Q = Reaction quotient

Standard Electrode Potentials

Potensi elektroda standar adalah ukuran kecenderungan setengah sel untuk mengalami reduksi dalam kondisi standar (298 K, tekanan 1 atm, dan konsentrasi 1 M). Nilai-nilai ini dirujuk terhadap elektroda hidrogen standar (SHE), yang memiliki potensi elektroda standar yang ditetapkan sebesar 0 V.

Potensi elektroda standar digunakan untuk menghitung potensial sel standar (E°cell) dari sel galvanik:

E°cell = E°cathode - E°anode

Applications of Galvanic Cells

Sel galvanik banyak digunakan dalam berbagai aplikasi, termasuk:

• Batteries: Batteries are a common example of galvanic cells. They are used to power a wide range of devices, from smartphones and laptops to cars and power tools.
  • Dry Cells: Dry cells are a type of battery commonly used in flashlights and portable electronic devices. They use a paste-like electrolyte instead of a liquid electrolyte.
  • Lead-Acid Batteries: Lead-acid batteries are used in cars and other vehicles. They are rechargeable and have a high energy density.
  • Lithium-Ion Batteries: Lithium-ion batteries are used in smartphones, laptops, and electric vehicles. They have a high energy density and a long lifespan.
• Fuel Cells: Fuel cells convert the chemical energy of a fuel (e.g., hydrogen) into electricity. They are more efficient than traditional combustion engines and produce fewer emissions.
• Corrosion Prevention: Galvanic cells can be used to protect metals from corrosion. This is done by connecting the metal to be protected to a more reactive metal, which will corrode instead.

Applications of Electrolytic Cells

Sel elektrolitik digunakan dalam berbagai proses industri, termasuk:

• Electroplating: Electroplating is the process of coating a metal object with a thin layer of another metal. This is done to improve the appearance, durability, or corrosion resistance of the object.
• Electrolysis of Water: Electrolysis of water is the process of using electricity to split water into hydrogen and oxygen. This process can be used to produce hydrogen fuel.
• Production of Metals: Electrolytic cells are used to extract metals from their ores. For example, aluminum is produced by the electrolysis of aluminum oxide.
• Chlor-Alkali Process: The chlor-alkali process uses electrolysis to produce chlorine gas, hydrogen gas, and sodium hydroxide from brine (a concentrated solution of sodium chloride).

Examples of Galvanic and Electrolytic Cells

Contrasting Electrode Polarities

Perbedaan penting antara sel galvanik dan sel elektrolitik terletak pada polaritas elektroda.

• Galvanic Cells:
  • Anode: Negatif (sumber elektron)
  • Cathode: Positif (penerima elektron)
• Electrolytic Cells:
  • Anode: Positif (terhubung ke terminal positif dari sumber daya eksternal)
  • Cathode: Negatif (terhubung ke terminal negatif dari sumber daya eksternal)

Polaritas elektroda dalam sel elektrolitik berlawanan dengan polaritas pada sel galvanik karena sumber daya eksternal memaksa elektron mengalir ke arah yang berlawanan.

Cell Diagrams and Conventions

Diagram sel adalah representasi singkat dari sel elektrokimia. Mereka memberikan informasi tentang komposisi elektroda, elektrolit, dan pengaturan sel.

• Galvanic Cell Diagram: Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
  • The single vertical lines (|) represent a phase boundary between the electrode and the electrolyte solution.
  • The double vertical lines (||) represent the salt bridge or porous membrane.
• Electrolytic Cell Diagram: Typically, electrolytic cell diagrams are not used as frequently as galvanic cell diagrams because the focus is on the overall reaction and the external power source.

Quantitative Aspects of Electrolysis: Faraday's Laws

Hukum Faraday tentang elektrolisis mengaitkan jumlah zat yang diproduksi atau dikonsumsi pada elektroda selama elektrolisis dengan jumlah listrik yang melewati sel.

• Faraday's First Law: The mass of a substance produced or consumed at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the cell.
• Faraday's Second Law: The masses of different substances produced or consumed at the electrodes during electrolysis by the same quantity of electricity are proportional to their equivalent weights.

The quantity of electricity (Q) is related to the current (I) and time (t) by the equation:

Q = I * t

The number of moles of electrons (n) transferred during electrolysis is related to the quantity of electricity (Q) and Faraday's constant (F) by the equation:

n = Q / F

Limitations and Considerations

• Overpotential: In electrolytic cells, the actual voltage required to drive a non-spontaneous reaction may be higher than the theoretical voltage calculated from standard electrode potentials. This additional voltage is called overpotential and is due to various factors, such as electrode kinetics and concentration polarization.
• Electrode Material: The choice of electrode material is crucial in both galvanic and electrolytic cells. The electrode material must be conductive, chemically inert, and have a high overpotential for unwanted side reactions.
• Electrolyte Concentration: The concentration of the electrolyte can affect the cell potential and the rate of the reaction. In galvanic cells, the Nernst equation can be used to calculate the cell potential under non-standard conditions.
• Temperature: Temperature can also affect the cell potential and the rate of the reaction. In general, increasing the temperature will increase the rate of the reaction.

Future Trends

The field of electrochemistry is constantly evolving, with new materials and technologies being developed. Some of the future trends in galvanic and electrolytic cells include:

• Advanced Battery Technologies: Research is ongoing to develop batteries with higher energy densities, longer lifespans, and improved safety. This includes the development of new electrode materials, electrolytes, and cell designs.
• Electrocatalysis: Electrocatalysis is the use of catalysts to improve the efficiency of electrochemical reactions. This is particularly important for fuel cells and electrolytic cells.
• Electrochemical Sensors: Electrochemical sensors are used to detect and measure a wide range of substances. These sensors are used in environmental monitoring, medical diagnostics, and industrial process control.
• Green Chemistry: Electrochemical methods are increasingly being used in green chemistry to develop more sustainable and environmentally friendly chemical processes.

Conclusion

Sel galvanik dan sel elektrolitik adalah dua jenis sel elektrokimia yang berbeda dengan prinsip kerja dan aplikasi yang berbeda. Sel galvanik memanfaatkan reaksi redoks spontan untuk menghasilkan energi listrik, sedangkan sel elektrolitik menggunakan energi listrik untuk mendorong reaksi redoks non-spontan. Memahami perbedaan antara kedua jenis sel ini sangat penting dalam berbagai bidang ilmiah dan industri.