General Chemistry
Electrolytic cells are a type of electrochemical cell where oxidation and reduction reactions occur. Unlike galvanic cells, electrolytic cells require an external voltage source, such as a battery, to function. The two electrodes in solution containing ionic compounds called electrolytes allow redox reactions and electron transfer to occur. The first electrode, known as the anode, is the site of oxidation and carries a positive charge. Anions from the cell solution are attracted to the anode. The second electrode, the cathode, is where reduction takes place and carries a negative charge. Cations within the cell solution are attracted to the negatively charged cathode.
Electrolytic cells have a positive ΔG, meaning they house non-spontaneous reactions that require energy input. They perform electrolysis, using electricity to drive non-spontaneous reactions. These cells have a negative electromotive force (EMF), with the amount of pure product produced being proportional to the moles of electrons transferred between electrodes. Electrolytic cells can be used to produce pure metals or gas and the amount produced can be calculated using the equation: moles of metal = I T / N F.
Lesson Outline
<ul> <li>Introduction to electrolytic cells</li> <ul> <li>Comparison with galvanic cells: galvanic cells generate voltage, electrolytic cells require external voltage source</li> <li>Rechargeable batteries as electrolytic cells</li> </ul> <li>Structure of an electrolytic cell</li> <ul> <li>Two electrodes in solution containing ionic compounds called electrolyte</li> <li>Anode (site of oxidation)</li> <li>Cathode (site of reduction)</li> </ul> <li>Charge and electron flow in electrolytic cells</li> <ul> <li>Anode is attached to the positive end of a battery</li> <li>Cathode is attached to the negative end of a battery</li> <li>Electrons flow from the anode to the cathode</li> <li>Current flows from the cathode to the anode</li> </ul> <li>Properties of electrolytic cells</li> <ul> <li>Positive delta G (non-spontaneous reactions)</li> <li>Negative electromotive force (EMF)</li> <li>Electrodes can be in the same compartment and made of any material</li> </ul> <li>Applications of electrolytic cells</li> <ul> <li>Obtaining pure elements from compounds</li> <li>Extracting metals from ore</li> </ul> <li>Calculating moles of product in an electrolytic cell</li> <ul> <li>Faraday's equation: moles of metal = I x T / (n x F)</li> </ul> </ul>
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FAQs
Galvanic cells are devices that generate electrical energy through spontaneous redox reactions, whereas electrolytic cells use electrical energy to drive non-spontaneous redox reactions. In a galvanic cell, such as a battery or fuel cell, the reaction produces a flow of electrons, which creates an electric current. In an electrolytic cell, an external voltage source is used to apply a potential difference, causing the reaction to proceed in the non-spontaneous direction. Applications of galvanic cells include batteries and fuel cells, while electrolytic cells are commonly used in electroplating, electrosynthesis, and electrolysis of various compounds.
In both galvanic and electrolytic cells, the anode is the electrode where oxidation occurs, and the cathode is the electrode where reduction takes place. The primary difference is in the direction of the electron flow. In a galvanic cell, electrons flow spontaneously from the anode (where the material gets oxidized) to the cathode (where the material gets reduced). In an electrolytic cell, the anode and cathode are swapped relative to what they would be in a galvanic cell, so electron flow from anode to cathode is nonspontaneous and must be driven by an external voltage source.
Redox reactions are fundamental to the functioning of both galvanic and electrolytic cells. In these reactions, the transfer of electrons from one chemical species (oxidation) to another (reduction) occurs. This electron transfer allows the generation of electrical energy in galvanic cells, while in electrolytic cells, the externally supplied electrical energy drives the redox reactions in a non-spontaneous manner. The coupled redox reactions are essential to various applications, such as energy storage in batteries, large-scale production of elements and chemicals through electrolysis, and metal surface treatments like electroplating.
Rechargeable batteries, such as lithium-ion or nickel-metal hydride batteries, function as galvanic cells when discharging and electrolytic cells when recharging. When discharging, the battery operates as a galvanic cell, generating electricity through spontaneous redox reactions. Upon recharging, the application of an external voltage source reverses the reactions, and the battery operates as an electrolytic cell, thus restoring the original chemical compositions of the electrodes. This reversible redox process allows the rechargeable battery to be used multiple times, switching between the galvanic and electrolytic cell modes.
ΔG, or Gibbs free energy change, and electromotive force (EMF) are related parameters that help determine the spontaneity of redox reactions in electrochemical and electrolytic cells. In general, if ΔG is negative for a reaction, it is considered spontaneous, and when it is positive, the reaction is non-spontaneous. EMF, or cell potential, is a measure of the tendency of the redox reaction to proceed in a given direction. A positive EMF indicates a spontaneous reaction, while a negative EMF signifies non-spontaneity. In galvanic cells, spontaneous reactions occur with positive EMF, while in electrolytic cells, a non-spontaneous reaction is driven by applying an external voltage greater than the absolute value of negative EMF.
