7.2 Electrochemistry and Galvanic Cells
2 min read•july 25, 2024
Electrochemical cells are the unsung heroes of modern technology. From powering our devices to detecting diseases, these tiny powerhouses convert chemical energy into electrical energy, revolutionizing how we live and work.
Understanding the components and principles of electrochemical cells is crucial. We'll explore how anodes, cathodes, and salt bridges work together to create electricity, and how cell potentials are calculated and applied in real-world scenarios like biosensors and .
Electrochemical Cells and Their Applications
Components of galvanic cells
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- oxidizes, acts as negative electrode, loses electrons (zinc electrode in Daniell cell)
- reduces, acts as positive electrode, gains electrons (copper electrode in Daniell cell)
- Salt bridge maintains electrical neutrality, allows ion flow between half-cells (KCl solution)
- Voltmeter measures cell potential difference between electrodes
- Half-cells separate compartments for each electrode, contain electrolyte solutions (CuSO₄, ZnSO₄)
Calculation of standard cell potential
- Standard potentials tabulated for half-reactions, measured relative to standard hydrogen electrode (SHE)
- Cell potential calculation uses formula , always positive for spontaneous reactions
- relates cell potential to non-standard conditions
- Concentration effects impact cell potential, higher reactant concentration or lower product concentration increases potential
Gibbs free energy vs cell potential
- Gibbs free energy and cell potential related by , n represents electrons transferred, F is Faraday constant
- Spontaneous reactions have negative and positive
- Standard conditions use to calculate equilibrium constants
Applications in biosensors and fuel cells
- Biosensors utilize enzyme-based electrochemical reactions (glucose meters), detect specific DNA sequences (genetic testing)
- Fuel cells convert chemical energy to electrical energy (hydrogen fuel cells in vehicles), utilize bacteria for electricity generation (microbial fuel cells for wastewater treatment)
- Implantable medical devices employ long-lasting lithium-iodine (pacemakers), rechargeable batteries for continuous operation (cochlear implants)
Key Terms to Review (18)
Amperage: Amperage, or current, refers to the flow of electric charge through a conductor, measured in amperes (A). It plays a crucial role in electrochemistry and galvanic cells by determining how much electric current is produced or consumed during chemical reactions, thus influencing the overall efficiency and performance of these systems.
Anode: An anode is the electrode in an electrochemical cell where oxidation occurs, meaning it loses electrons. In a galvanic cell, the anode is often negative because it donates electrons to the external circuit, driving the electrochemical reaction. Understanding the role of the anode is essential in analyzing how cells generate electrical energy through spontaneous chemical reactions.
Batteries: Batteries are electrochemical devices that convert chemical energy into electrical energy through redox reactions. They play a crucial role in providing portable energy sources for various applications, from small electronic devices to electric vehicles. Understanding how batteries work involves knowledge of electrochemistry, galvanic cells, and the flow of electrons in a circuit.
Cathode: The cathode is the electrode in an electrochemical cell where reduction occurs, meaning it gains electrons. This electrode plays a crucial role in galvanic cells, which convert chemical energy into electrical energy, as well as electrolytic cells, where electrical energy drives a non-spontaneous reaction. The cathode is essential for understanding how these systems operate, as it interacts with ions in the electrolyte to facilitate electron flow.
Current: Current refers to the flow of electric charge, typically measured in amperes (A), which is essential for understanding electrochemical processes and the operation of galvanic cells. It represents the movement of electrons through a conductor, driven by a potential difference. In the context of electrochemistry, current plays a crucial role in facilitating redox reactions and enabling the conversion of chemical energy into electrical energy in galvanic cells.
Daniel Cell: The Daniel Cell, also known as the Daniell cell, is a type of electrochemical cell that converts chemical energy into electrical energy through redox reactions. It consists of two half-cells, one with zinc and the other with copper, which are connected by a salt bridge. This setup enables the flow of electrons from the anode (zinc) to the cathode (copper), illustrating key principles of electrochemistry and galvanic cells.
Electrode Potential: Electrode potential is the measure of the ability of an electrode to drive an electrochemical reaction, quantified in volts (V). It represents the tendency of a chemical species to be reduced or oxidized at the electrode surface, and is crucial in understanding how cells generate electric current through redox reactions. The value of the electrode potential helps predict the direction of electron flow and the feasibility of reactions within electrochemical cells.
Electrolytic cell: An electrolytic cell is an electrochemical cell that uses an external voltage source to drive a non-spontaneous chemical reaction. This type of cell involves the process of electrolysis, where electrical energy is converted into chemical energy to cause a reaction, often resulting in the decomposition of compounds. Electrolytic cells are crucial in various applications, such as electroplating, electrorefining, and the production of gases like hydrogen and oxygen.
Faraday's Laws of Electrolysis: Faraday's Laws of Electrolysis consist of two fundamental principles that quantify the relationship between electric current and chemical reactions occurring during electrolysis. These laws help to predict the amount of substance transformed at the electrodes based on the amount of electric charge passed through the electrolyte solution, linking concepts of electrochemistry with practical applications in galvanic cells.
Fuel cells: Fuel cells are electrochemical devices that convert chemical energy from fuels, typically hydrogen, directly into electricity through a chemical reaction with oxygen or another oxidizing agent. This process is highly efficient and produces only water and heat as byproducts, making fuel cells an attractive alternative energy source in various applications, including transportation and stationary power generation.
Galvanic cell: A galvanic cell is an electrochemical cell that converts chemical energy into electrical energy through spontaneous redox reactions. It consists of two half-cells, each containing an electrode and an electrolyte, where oxidation occurs at the anode and reduction occurs at the cathode. This process generates a flow of electrons through an external circuit, providing electric power.
Michael Faraday: Michael Faraday was a renowned English scientist who made significant contributions to the fields of electromagnetism and electrochemistry in the 19th century. His groundbreaking work laid the foundation for modern electrical engineering and chemistry, particularly through his exploration of oxidation-reduction reactions and the principles governing electrochemical cells.
Nernst Equation: The Nernst Equation is a mathematical formula that relates the concentration of ions to the voltage or electromotive force (EMF) of an electrochemical cell. It is used to calculate the equilibrium potential of an ion based on its concentration gradient across a membrane, providing insights into how changes in concentration can affect the cell's electrical potential. This equation is fundamental in understanding oxidation-reduction reactions and the behavior of galvanic cells.
Non-spontaneous reaction: A non-spontaneous reaction is a chemical reaction that does not occur naturally under standard conditions and requires an input of energy to proceed. These reactions often involve processes that are thermodynamically unfavorable, meaning they have a positive Gibbs free energy change ($$\Delta G > 0$$). In electrochemistry, non-spontaneous reactions are critical when discussing the function of electrolytic cells, where external energy is needed to drive the reaction forward.
Ohm's Law: Ohm's Law states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points and inversely proportional to the resistance (R) of the conductor. This fundamental principle is crucial in understanding how electrical circuits function, especially in the context of electrochemistry and galvanic cells, where the relationship between voltage, current, and resistance affects the efficiency and behavior of electrochemical reactions.
Oxidation: Oxidation refers to the process in which an atom, ion, or molecule loses electrons, resulting in an increase in its oxidation state. This process is fundamental to many chemical reactions, particularly oxidation-reduction reactions, where it often occurs simultaneously with reduction—the gain of electrons by another species. Understanding oxidation is essential for grasping how energy is transferred in chemical processes and the principles of electrochemistry.
Reduction: Reduction is a chemical process where a substance gains electrons, resulting in a decrease in its oxidation state. This process is fundamental to oxidation-reduction reactions, commonly known as redox reactions, where reduction occurs simultaneously with oxidation. Understanding reduction is crucial as it plays a vital role in energy transfer, chemical reactions, and electrochemical processes.
Voltage: Voltage, also known as electric potential difference, is the measure of electric potential energy per unit charge between two points in an electric field. It drives the flow of electric current in circuits and is crucial in the operation of electrochemical systems, influencing both the movement of electrons and the chemical reactions that occur in galvanic cells.