The respiratory chain is a set of red-ox reactions as a result of which H2 and electrons are transferred to O2 with the release of H2O and energy. As a result oxidative reactions In the Krebs cycle, catalyzed by dehydrogenases, protons and electrons are transferred from organic substrates to the cofactors NAD and FAD, reducing them to NADH and FADH2. These substances have high energy potential. Electrons from them are transferred to O2 through a series of red-ox reactions. Oxidation organic matter in cells, accompanied by the consumption of O2 and the formation of H2O, is called tissue respiration, and the electron transport chain is called the respiratory chain.
NADH and FADH2 molecules, formed in the oxidation reactions of carbohydrates, fatty acids, alcohols and AA, then enter the mitochondria, where the process of oxidative phosphorylation is carried out by enzymes of the respiratory chain.
The respiratory chain is part of the process of oxidative phosphorylation. Components of the respiratory chain catalyze the transfer of electrons from NADH + H+ or reduced ubiquinone (QH2) to molecular oxygen. Due to the large difference in the redox potentials of the donor (NADH + H+ and, accordingly, (QH2) and acceptor (O2), the reaction is highly exergonic. Most of the energy released in this case is used to create a proton gradient and, finally, to form ATP with using ATP synthase.
The principle of operation of the respiratory chain:
1) NADH and FADH2 formed in catabolic reactions transfer hydrogen atoms (i.e., hydrogen protons and electrons) to the enzymes of the respiratory chain.
2) Electrons move through the enzymes of the respiratory chain and lose energy.
3) This energy is used to pump H+ protons from the matrix into the intermembrane space.
4) At the end of the respiratory chain, electrons strike oxygen and reduce it to water.
5) H+ protons rush back into the matrix and pass through ATP synthase.
6) At the same time, they lose energy, which is used for the synthesis of ATP.
Thus, the reduced forms of NAD and FAD are oxidized by enzymes of the respiratory chain, due to which phosphate is added to ADP, i.e. phosphorylation. Therefore, the entire process is called oxidative phosphorylation.
In total, the electron transport chain includes about 40 different proteins, which are organized into 4 large membrane-bound multienzyme complexes. There is also another complex that is not involved in electron transfer, but synthesizes ATP.
There are 2 inputs in the respiratory chain: 1. Protons enter the chain via NADH; 2. As part of FADN2
Characteristics of the components of the respiratory chain (enzymatic complexes):
1) NADH dehydrogenase (NADH-CoQ oxidoreductase) is built into the inner membrane of mitochondria. This is a flavin-dependent enzyme, which includes vitamin B2. Complex, has 2 prosthetic groups: FMN (flavin mononucleotide active form vitamin B2) and iron-sulfur proteins (FeS proteins). The Fe atoms included in the FeS centers are non-heme (not part of the heme). The active center of NADHDH faces the mitochondrial matrix. NADH dehydrates NADH (splits off H2) and transfers protons and electrons first to FMN, and then through FeS centers to CoQ (reduced and converted into CoQH2 or ubiquinol).
Function: a) Receives electrons from NADH and transfers them to coenzyme Q (ubiquinone).
b) Transfers 4 H+ ions to the outer surface of the inner mitochondrial membrane.
2) CoQ (ubiquinone) non-protein carrier, is in a dissolved state, because is fat-soluble (dissolves in the lipid layer of membranes). Therefore, it can move both along and across the membrane (not charged). Therefore, it accepts electrons and protons from FADH2, i.e. h/z 2nd entrance to the respiratory chain. It is called an electron collector.
3) Cytochromes (b, c1, c, a, a3) complex proteins (hemeproteins), the non-protein part of which is heme containing Fe3+ (oxidized form). Fe heme can reversibly accept and donate electrons.
4) UbiquinolDH (CoQ-cytochrome c-oxidoreductase) is an enzyme complex consisting of cytochromes b and c1, which also includes FeS centers. Function:
a) Receives electrons from coenzyme Q and transfers them to cytochrome c (in this case Fe is reduced to 2x valence); b) Transfers 2 H+ ions to the outer surface of the inner mitochondrial membrane.
5) Cytochrome c-oxygen oxidoreductase - This complex contains cytochromes a and a3, it is also called cytochrome oxidase, contains 6 in total polypeptide chains. The complex also contains 2 copper ions. Function: a) Accepts electrons from cytochrome c and transfers them to oxygen to form water. b) Transfers 4 H+ ions to the outer surface of the inner mitochondrial membrane.
6) ATP synthase a complex consisting of many protein chains, divided into two large groups: one group forms the Fo subunit (pronounced with the sound “o” and not “zero” because it is oligomycin-sensitive) its function is channel-forming, along it, the hydrogen protons pumped out rush into the matrix. The other group forms the F1 subunit; its function is catalytic; it is the one that synthesizes ATP using the energy of protons.
"Chemiosmatic theory of conjugation, oxidation and phosphorylation" Mitchell:
“The transfer of electrons along the respiratory chain from NADH to O2 is accompanied by the pumping of protons from the mitochondrial matrix through the inner membrane into the intermembrane space. The transfer of protons is carried out due to the free energy released during the transfer of electrons along the redox potential gradient.”
Protons cannot return to the matrix, because The inner membrane of mitochondria is impermeable to them and to other charged particles. As a result, “+” charges are concentrated on the outside of the inner membrane, and “-” on the inside. An electrical potential difference (ΔΨ, “delta psi”) occurs across the membrane. Protons accumulate in the intermembrane space, the pH decreases, i.e. the environment will be acidic. And in the matrix there are fewer protons, a gradient of chemical potential (ΔpH) arises. ΔμH+ = ΔΨ + ΔрН (Mitchel’s electrochemical potential).
The most active transport of protons into the intermembrane space occurs at the points of conjugation, oxidation and phosphorylation. CoQ plays an important role in the process of proton transport. For every pair of electrons transferred along the respiratory chain from NADH to O2, 3 pairs of protons are produced. If electrons are transferred from FADH2, then 2 pairs of protons. Protons can only return to the matrix through the ion channels of the ATP synthase enzyme.
ΔμH+ generated by protons at each of the conjugation points is used for the synthesis of the first ATP molecule. The synthesized ATP passes into the mitochondrial matrix.
We have the largest information database in RuNet, so you can always find similar queries
This material includes sections:
Primary structure of proteins. Species specificity of proteins. Hereditary changes in the primary structure. Protein polymorphism. Hereditary proteinopathies: sickle cell anemia, other examples.
Conformation of protein molecules (secondary and tertiary structures). Types of intramolecular bonds in proteins. The role of the spatial organization of the peptide chain in the formation of active centers. Conformational changes during protein functioning.
Quaternary structure of proteins. Cooperative changes in protomer conformation. Examples of the structure and functioning of oligomeric proteins: hemoglobin (compared to myoglobin), allosteric enzymes.
Concept of enzymes. Specificity of enzyme action. Enzyme cofactors. Dependence of the rate of enzymatic reactions on the concentration of the substrate, enzyme, temperature and pH. Principles of enzyme quantification. Activity units.
The concept of the active center of an enzyme. Mechanism of action of enzymes. Enzyme inhibitors: reversible and irreversible, competitive. The use of inhibitors as drugs.
Regulation of enzyme action: allosteric mechanisms, chemical (covalent) modification. Protein-protein interactions. Examples of metabolic pathways regulated by these mechanisms. Physiological significance of regulation of enzyme action.
The role of enzymes in metabolism. Variety of enzymes. The concept of classification. Hereditary primary enzymopathies: phenylketonuria, alkaptonuria. Other examples of hereditary enzymopathies. Secondary enzymopathies. The importance of enzymes in medicine.
The concept of catabolism and anabolism and their relationship. Endergonic and exergonic reactions in metabolism. Methods of electron transfer. Features of the course of oxidative reactions in the body. Stages of breakdown of substances and release of energy (stages of ka
Oxidoreductases. Classification. Characteristics of subclasses. NAD-dependent dehydrogenases. Structure of oxidized and reduced forms. The most important substrates of NAD-dependent dehydrogenases. FAD-dependent dehydrogenases: succinate dehydrogenase and acylCoA dehydrogenase
Oxidative decarboxylation of pyruvate and the Krebs cycle: sequence of reactions, connection with the respiratory chain, regulation, significance.
Respiratory chain, components, structural organization. Electrochemical potential, its meaning.
Oxidative phosphorylation of ADP. Mechanism. Coupling and uncoupling of oxidation and phosphorylation in the respiratory chain. Ratio P/0. Regulation of the respiratory chain.
Substrate phosphorylation of ADP. Differences from oxidative phosphorylation. The main ways of using ATP. ADP-ATP cycle. The concept of free oxidation and its significance. Tissue features of redox processes.
Functions of carbohydrates. The body's need for carbohydrates. Digestion of carbohydrates. Disturbances in the digestion and absorption of carbohydrates. Unification of monosaccharides. The role of the liver in carbohydrate metabolism.
Biosynthesis and mobilization of glycogen: sequence of reactions, physiological significance. Regulation of glycogen metabolism. Glycogenoses and aglycogenoses.
Anaerobic breakdown of glucose: sequence of reactions, physiological significance. The role of anaerobic breakdown of glucose in muscles. The further fate of lactic acid.
Aerobic breakdown of glucose: sequence of reactions, physiological significance. The role of aerobic breakdown of glucose in muscles during muscular work. The role of aerobic glucose breakdown in the brain.
Glucose biosynthesis (gluconeogenesis): possible precursors, sequence of reactions. Glucose-lactate cycle (Cori cycle) and glucose-alanine cycle: physiological significance. The significance and regulation of gluconeogenesis from amino acids.
Pentose phosphate pathway for glucose conversion. Oxidative pathway for the formation of pentoses. An idea of the non-oxidative pathway for the formation of hexoses. Distribution, role, regulation.
Functions of lipids. Edible fats; daily intake rate, digestion, absorption of digestion products. Resynthesis of fats in intestinal cells. Chylomicrons, structure, significance, metabolism. Limits of changes in the concentration of fats in the blood.
Oxidation of glycerol and higher fatty acids. Sequence of reactions. Relationship between β-oxidation and the Krebs cycle and the respiratory chain. The physiological significance of fatty acid oxidation depending on the rhythm of nutrition and muscle activity.
Lipolysis and lipogenesis. Meaning. Dependence of lipogenesis on the rhythm of nutrition and food composition. Regulation of lipolysis and lipogenesis. Transport and use of fatty acids formed during fat mobilization.
Biosynthesis of fatty acids: sequence of reactions, physiological significance, regulation.
Pathways of formation and use of acetyl-CoA. Biosynthesis and significance of ketone bodies. The limits of changes in the concentration of ketone bodies in the blood are normal, during fasting and diabetes.
Cholesterol synthesis, regulation. Biological significance of cholesterol. Atherosclerosis. Risk factors for the development of atherosclerosis.
Transport lipoproteins in the blood: features of the structure, composition and functions of different lipoproteins. Role in the metabolism of fats and cholesterol. Limits of changes in the concentration of fats and cholesterol in the blood. Pathology of lipid metabolism.
Functions of peptides and proteins. Daily protein requirement. Digestion of proteins. Regulation of protein digestion. Pathology of protein digestion and absorption.
Decarboxylation of amino acids. His essence. Decarboxylation of histidine, serine, cysteine, ornithine, lysine and glutamate. The role of biogenic amines in the regulation of metabolism and functions.
Transamination of amino acids. Specificity of aminotransferases. The significance of transamination reactions. Indirect deamination of amino acids: sequence of reactions, enzymes, biological significance.
Formation and uses of ammonia. Urea biosynthesis: sequence of reactions, regulation. Hyperammonemia.
Metabolism of phenylalanine and tyrosine. Hereditary disorders of phenylalanine and tyrosine metabolism. The meaning of serine, glycine and methionine.
Creatine synthesis: sequence of reactions, meaning of creatine phosphate. Physiological creatinuria. The importance of creatine kinase and creatinine in diagnosis.
Nucleosides, nucleotides and nucleic acids, structure, meaning. Differences between DNA and RNA. Nucleoproteins. Digestion of nucleoproteins.
Catabolism of purine and pyrimidine bases. Hyperuricemia. Gout.
Biosynthesis of purine and pyrimidine nucleotides. Biosynthesis of deoxyribonucleotides. Regulation of these processes.
DNA replication: mechanism and biological significance. DNA damage, repair of damage and DNA replication errors.
Types of RNA: structural features, size and diversity of molecules, localization in the cell, functions. RNA biosynthesis (transcription). Structure of ribosomes and polyribosomes. Synthesis of aminoacyl-tRNA. Substrate specificity of aminoacyl-tRNA synthetases.
Biological code. The main components of the protein synthesizing system. Protein biosynthesis. Mechanism. Adapter function of tRNA and the role of mRNA in this process.
Regulation of protein biosynthesis. Induction and repression of protein synthesis using the example of the functioning of the lactose operon of Escherichia coli. Inhibitors of matrix biosynthesis: drugs, viral and bacterial toxins.
Hemoglobin. Structure. Synthesis and breakdown of hemoglobin. Forms of bilirubin. Ways of excretion of bilirubin and other bile pigments. Jaundice.
Protein fractions of blood plasma. Functions of blood plasma proteins. Hypo- and hyperproteinemia, the causes of these conditions. Individual blood plasma proteins: transport proteins, acute phase proteins.
Residual blood nitrogen. Hyperazotemia, its causes. Uremia.
Basic biochemical functions and features of the liver.
The relationship between the metabolism of fats, carbohydrates and proteins.
Biochemistry of regulation. Basic principles and meaning. Hierarchy of regulatory systems. Classification of intercellular regulators. Central regulation of the endocrine system: the role of liberins, statins and tropins.
Concept of receptors. The mechanism of action of hormones through intracellular receptors and plasma membrane receptors and second messengers (general characteristics).
Insulin. Structure, formation from proinsulin, metabolism, regulation of secretion. Effect on metabolism.
Diabetes. Pathogenesis. Metabolic disorders in diabetes mellitus. Determination of glucose tolerance in the diagnosis of diabetes mellitus.
Growth hormone, glucagon and other peptide hormones. Biological significance.
Hormones of the adrenal cortex. Synthesis, metabolism, regulation of secretion. Glucocorticosteroids, effect on metabolism. Hypo- and hypercortisolism
Structure, synthesis and metabolism of iodothyronines. Effect on metabolism. Hypo- and hyperthyroidism: mechanism of occurrence and consequences
Catecholamines. Synthesis, deposition and metabolism of catecholamines. Mechanism of action. Effect on metabolism
Functions of water in the body. Regulation of water metabolism by antidiuretic hormone
Functions of minerals. Regulation of salt metabolism by aldosterone and atrial hormones. Biochemical mechanisms of development of renal hypertension
Regulation of calcium and phosphorus metabolism. The role of parathyroid hormone and thyrocalcitonin. Vitamin D. The role of 1,25-dihydroxycalciferol in the regulation of calcium and phosphate. Rickets
Vitamins E. K and ubiquinone, their participation in metabolism
Participles and verbal adjectives
The letters N and НН in verbal adjectives and participles. Signs by which a part of speech can be determined (verbal adjective or participle). Difference between participle and adjective.
Training structure. Training process
The process of many years of training for athletes. Application of therapeutic physical culture. Adaptive Physical Culture and sports for the disabled. General Basics therapeutic physical culture.
Environment. Effect on the body. Answers to test questions
Eczema. Etiology. Classification
Eczema is a disease of the superficial layers of the skin, accompanied by polymorphism of rashes. Etiology. The causes of eczema can be external or internal.
Characteristics of frosted equipment
Diploma of work. Until now, system administrators have been limited in their choice of options for creating the central highways of their networks. With the advent of new technologies and the installation of vinyl, another problem is what to choose?
Living systems at all levels of organization are open systems. Therefore, the transport of substances through biological membranes is necessary condition life. Cell metabolic processes, bioenergetic processes, the formation of biopotentials, the generation of a nerve impulse, etc. are associated with the transfer of substances through membranes. Violation of the transport of substances through biomembranes leads to various pathologies. Treatment often involves drug penetration through cell membranes. The effectiveness of a drug largely depends on the permeability of the membrane. Great importance to describe the transport of substances has the concept of electrochemical potential.
Chemical potential of this substance m to is a quantity numerically equal to the Gibbs energy per mole of this substance. Mathematically, the chemical potential is defined as the partial derivative of the Gibbs energy, G, with respect to the amount of the kth substance, at constant temperature T, pressure P and the amounts of all other substances m l (l¹k).
m k = (¶G/¶m k) P , T , m
For a dilute solution of the concentration of substance C:
m = m 0 + RTlnC
where m 0 is the standard chemical potential, numerically equal to the chemical potential of a given substance at its concentration of 1 mol/l in solution.
Electrochemical potential m- a value numerically equal to the Gibbs energy G per one mole of a given substance placed in an electric field.
For dilute solutions
m = m o + RTlnC + ZFj (1)
where F = 96500 C/mol is the Faraday number, Z is the charge of the electrolyte ion (in elementary charge units), j is the potential electric field, T [K] – temperature.
Transport of substances across biological membranes can be divided into two main types: passive and active.
What will we do with the received material:
If this material was useful to you, you can save it to your page on social networks:
| Tweet |
All topics in this section:
Vitebsk
EE "VSU named after. P. M. Masherova" UDC 577 (075) BBK 28.071ya73 B 63 Published by decision of the scientific and methodological council
Biophysics as a science. Biophysics subject
Theoretical questions: 1. Subject and tasks of biophysics. Levels of biophysical research; research methods and requirements for them.
2. Isto
Subjects of the task of biophysics. History of the development of biophysics
Biophysics is a science that studies the physical and physicochemical processes that occur in biosystems at different levels of organization and are the basis of physiological acts. Its emergence was due to
Biophysics methodology Let us introduce the definition of the following terms: object of biophysical research, biological system, technique, method, methodology.- a set of interconnected certain patterns
Thermodynamics of biological processes
Theoretical questions: 1. Subject and methods of thermodynamics. Basic concepts of thermodynamics.
2. State parameters (intensive and extensive) Function with
Theorem of I. Prigogine. Onsager equations I. Prigogine’s postulate is that the total change in entropy dS open system
can occur independently or due to exchange processes with the external environment (deS
Relationship between entropy and information. The amount of biological information, its value
According to Boltzmann's formula, entropy is defined as the logarithm of the number of microstates possible in a given macroscopic system: S = kB ln W
Biomembranology. Structure and properties of biological membranes
Theoretical questions: 1. Structure of cell membranes.
2. Types of biological membranes. 3. Proteins in the structure of cell membranes, their structure Basic functions of biological membranes Elementary living system
capable of independent existence, development and reproduction is
living cell
- the basis of the structure of all animals and plants. The most important conditions of existence
Structure of biological membranes
The first model of the structure of biological membranes was proposed in 1902. It was noticed that substances that are highly soluble in lipids penetrate best through membranes, and on the basis of this it was made
Phase transitions of lipids in membranes A substance at different temperatures, pressures, and concentrations of chemical components can be in different physical states, for example, gaseous, liquid, solid, plasma. Crystalline Physics of substance transport processes through biological membranes
Theoretical questions: 1. Paths of penetration of substances through cell membranes.
2. driving forces membrane transport.
3. Types of transport
Passive transport of substances across a membrane
Passive transport is the transfer of matter from places with
great value electrochemical potential to places with its lower value. Active transport of substances. Ussing's experience
Active transport is the transfer of a substance from places with a lower electrochemical potential to places with a higher value.
One of the most important functions of a biological membrane is the generation and transmission of biopotentials. This phenomenon underlies the excitability of cells, the regulation of intracellular processes, the functioning of the nervous system,
Propagation of a nerve impulse along an excitable fiber
If an action potential has formed in any part of the excitable membrane, the membrane is depolarized, and excitation spreads to other parts of the membrane. Let us consider the propagation of excitations
Properties of ion channels of cell membranes
The excitable membrane model according to the Hodgkin-Huxley theory assumes the controlled transport of ions across the membrane. However, the direct passage of ions through the lipid bilayer is very difficult. Therefore he led
Types of controlled channels and pumps
1) The “gate” of the channel is connected by a system of “levers” to a dipole, which can be rotated
Participation of membranes in the transmission of intercellular information
An important property of all living beings is the ability to perceive, process and transmit information using biological membranes. Despite the enormous variety of different systems for obtaining
G proteins and second messengers
From the first link, the receptor (R), the signal is transmitted to the so-called N- or G-proteins - membrane proteins that are activated by the binding of guanosine triphosphate (GTP). G proteins are capable of transmitting information
Molecular basis of nerve impulse conduction in nerve fibers and synapses
Nature has created two fundamentally different ways intercellular signaling. One of them is that messages are transmitted using electric current; the second uses molecules, n
Special mechanisms for the transport of substances through the biomembrane (endo- and exocytosis)
Transport proteins ensure the penetration of many small polar molecules through cell membranes, but they are not capable of transporting macromolecules, for example, proteins, polynucleotides
Biophysics as a science
1. Remizov A.N. Medical and biological physics: textbook. for universities / A.N. Remizov, A.G. Maksina, A.Ya. Potapenko. – M., 2003. – P. 14–17.
2. Biophysics: textbook. for universities / V. F. Antonov [and
Biophysics of membranes. Structure and functions of biological membranes. Dynamics of biomembranes. Model lipid membranes
1. Remizov A.N. Medical and biological physics: textbook. for universities / A.N. Remizov, A.G. Maksina, A.Ya. Potapenko. – M., 2003. – P. 184–190.
1. Remizov A.N. Medical and biological physics: textbook. for universities / A.N. Remizov, A.G. Maksina, A.Ya. Potapenko. – M., 2003. – P. 191–213.
2. Biophysics: textbook. for universities / V.F. Antonov [
Lecture 15 1. Concept of electrochemistry . Atoms consist of charged particles - nuclei (+) and electrons (-), but in general they are electrically neutral. The presence of electrical charges may not be noticeable. But sometimes we encounter electrification. We comb our hair, but the hair on our head is flying away. Clothes stick to the body, and you can even hear the crackling sound of electrical discharges. This reveals one universal phenomenon - the emergence of electric charges at phase boundaries. Contacting surfaces sometimes spontaneously, sometimes with the expenditure of work (the case of electrification by friction) acquire opposite electric charges . Besides the obvious examples, surface charges are the cause of electric current in batteries; operation of thermoelements; charges on membranes nerve cells
ensure the conduction of nerve impulses; charges on nanoparticles stabilize dispersed systems, etc. The name electricity itself arose from the ability of amber to electrify (in Greek hlektro - amber.) Chapter physical chemistry , which studies the relationship between chemical and electrical phenomena, is called electrochemistry . The main problems of electrochemistry are the occurrence of electrical phenomena during chemical reactions and the course of chemical reactions
when exposed to electricity. The founders of electrochemistry are considered to be two Italian doctors, Luigi Galvani (1737–1798, Bologna) and Alessandro Volta (1745–1827). To the root galvano
there are 15 articles in the BME.
Galvanocaustics
Galvanization
Galvanotropism, etc.
The name galvanic cell comes from the surname Galvani. An electrochemical system is a heterogeneous system in which electricity
due to a spontaneous reaction (galvanic cell) or a non-spontaneous reaction occurs due to the expenditure of electrical work (electrolyzer). A dual action of the system is possible: in the charged state it acts as a current source, and during the charging process as an electrolyzer. This device is called a battery. All curious people know this.
An electrochemical reaction is a reaction accompanied by the transfer of charges across the phase boundary. 2. Varieties of surface potentials
– Contact potential occurs at the interface between two metals. In the case of contact between zinc and copper, zinc, which more easily gives up electrons, is charged positively, and copper negatively. Excess charges are concentrated along the metal interface, forming an electrical double layer.
If such a bimetal is immersed in acid, then electrons that reduce H + ions leave the copper surface, and at the same time zinc ions from the metal surface go into solution:
– Diffusion potential occurs at the interface between two liquid electrolytes. These can be solutions of the same substance with different concentrations, or solutions different substances, or solution and solvent. Obviously, such a boundary is unstable. Ion diffusion occurs, which leads to the emergence of a potential difference. Let us assume that the system consists of solutions of potassium chloride and hydrogen chloride of the same concentration of 1 mol/l. There is diffusion of K + ions into the HCl solution and counter diffusion of H + ions into the KCl solution. The diffusion of hydrogen ions occurs at a higher rate (the direction is shown by a longer arrow), as a result of which there is an excess of positive charge on the side of the KCl solution, and a negative charge on the side of the acid solution. A potential jump φ diff occurs.
– Membrane potential occurs on a membrane characterized by selective permeability to ions of different nature. Let us imagine solutions of chloride of different concentrations, separated by a membrane that allows chlorine ions to pass through, but sodium ions not to pass through. Then a certain amount of Cl – ions will move from a solution with a higher concentration to a solution with a lower concentration. The remaining excess Na + ions attracts Cl – ions and stops transport across the membrane. A certain potential jump is established, corresponding to the equilibrium state.
– Electrode potential arises at the interface between metal (conductor of the 1st kind) and electrolyte (conductor of the 2nd kind). The electrode potential has highest value in electrochemistry, since the operation of chemical current sources is based on this phenomenon. A system consisting of metal and electrolyte is called an electrode. Next we will talk about a number of types of electrodes. Now, as an example, consider a metal ion electrode (electrode of the 1st kind) Cu / Cu 2+. A plate of copper metal is immersed in a solution of a copper salt, for example CuSO 4 . The electrode is conventionally written with the symbol Cu | Cu 2+, where the vertical line means the interface between the metal and the electrolyte.
The concentration of copper ions in the metal and, accordingly, their chemical potential is higher than in solution. Therefore, a certain number of Cu 2+ ions pass from the metal surface to the electrolyte. An excess of electrons remains on the metal. From the electrolyte side, ions with positive charges are attracted to the metal surface. An electric double layer (EDL) appears. As a result of the movement of ions in the solution, a certain number of ions are removed from the surface, being in the diffusion layer. The equilibrium value of the potential jump in the electrical double layer is established. This potential jump j is called the electrode potential.
Let's consider what the value of the electrode potential depends on. The separation of charges in a DEL means the expenditure of electrical work, and the transfer of substance particles in the form of ions from the metal into a solution is a spontaneous chemical process that overcomes electrical resistance. In a state of balance
W el = –W chemical
Let us transform this equation for one mole of metal ions Me z+ (in our example this is Cu 2+):
Where F– Faraday constant 96485.3383 C mol –1 (according to the latest data). By physical meaning this is a charge of 1 mole elementary charges. Metal ion activity a(Me z+) in the case of sufficiently dilute solutions can be replaced by concentration With(Me z+). By dividing the written expression by zF we obtain the equation for calculating the electrode potential:
At A(Me z +) = 1; j = j o = DG°/zF. We make the substitution:
This equation is called the Nernst equation. According to this equation, the electrode potential depends on the activity (concentration) of electrolyte ions a(Me z+), temperature E and the nature of the Me/Me system z+ , which is implied in the value of the standard electrode potential j o.
Let us take for comparison another electrode obtained by immersing a zinc plate in a solution of zinc sulfate, denoted by the symbol Zn|Zn 2+:
Zinc is a more active metal than copper. A larger number of Zn 2+ ions pass from the metal surface to the electrolyte, and a greater excess of electrons remains on the metal (all other things being equal). As a result, it turns out that
j o (Zn 2+)< j о (Cu 2+)
In the activity series you know, metals are arranged in order of increasing standard electrode potentials.
3. Galvanic cell
Let's consider a system composed of two electrodes - copper and zinc. The electrolytes are connected by a curved tube filled with a potassium chloride solution. Ions can move through such a bridge. The mobilities of K + and Cl – ions are almost the same, and thus the diffusion potential is minimized. Metals are connected with copper wire. The contact between metals can be opened if necessary. A voltmeter can also be placed in the circuit. This system is an example of a galvanic cell, or chemical source current The electrodes in a galvanic cell are called half-elements.
When the contact between the metals is open, equilibrium values of the electrode potentials are established at the metal-electrolyte interfaces. Chemical processes are absent in the system, but there is a potential difference between the electrodes
Δφ = jо (Cu 2+) – jо (Zn 2+)
When the contact is closed, electrons begin to move from the zinc plate, where their surface concentration is higher and the potential is lower, to the copper plate. The potential on copper decreases, and on zinc it increases. The balance has been disrupted. On the copper surface, electrons react with ions in the electrical double layer to form atoms:
Cu 2+ + 2e – = Cu
The copper potential is again approaching equilibrium. On the surface of zinc, the lack of electrons is compensated by the transition of ions into the electrical double layer, and from it into the electrolyte:
Zn = Zn 2+ + 2e –
The potential on zinc is again approaching equilibrium. Processes on the electrodes maintain a potential difference between them, and the flow of electrons does not stop. Electric current flows in the circuit. In a copper half-cell, copper is deposited on the metal surface and the concentration of Cu 2+ ions in the solution decreases. In the zinc half-cell, the mass of the metal decreases, and at the same time the concentration of Zn 2+ ions in the solution increases. The galvanic cell operates as long as the conductor is closed, and until the initial components - zinc metal and copper salt - are used up. Adding up the reactions occurring at the electrodes, we obtain the overall reaction equation in the galvanic cell:
Zn + Cu 2+ = Zn 2+ + Cu, Δ r H= -218.7 kJ; Δr G= -212.6 kJ
If the same reaction is carried out under normal conditions between zinc and copper sulfate, then all the energy is released in the form of heat equal to 218.7 kJ. The reaction in a galvanic cell gives electrical work 212.6 kJ, and only 6.1 kJ remains as heat.
The potential difference between the electrodes in a galvanic cell is a measurable quantity called electromotive force , EMF. This is a positive value:
The potentials of the electrodes and the EMF of the element do not depend on the size of the system, but only on the materials and conditions. Therefore, current sources have different sizes depending on their purpose, as we see in commercially available batteries. Electrodes for practical and scientific measurements can be microsized, allowing them to be inserted into a cell to measure membrane potentials.
The considered galvanic cell in the standard state has EMF = 1.1 V.
EMF = |j o (Cu 2+ /Cu) - j o (Zn 2+ /Zn)| = 1.1 V.
The following conventional notation for the galvanic circuit is used:
|
|
Anode is an electrode at which oxidation occurs.
Cathode is the electrode at which reduction occurs.
The potential difference between the electrodes is measured with a voltmeter, but the electrode potential of an individual electrode cannot be determined experimentally. Therefore, the potential of a conventionally selected electrode is taken as zero, and the potentials of all other electrodes are expressed relative to it. A standard hydrogen electrode was taken as the zero electrode. It consists of a platinum plate coated with platinum black and dipped into an acid solution, into which hydrogen is passed under a pressure of 101.3 kPa. The electrode is written as follows:
By convention, jº(Pt, H 2 | H+) = 0 V.
If the hydrogen electrode in the galvanic cell under study turns out to be the cathode, then the second electrode in this element is the anode, and its potential is negative. In the opposite case, when the hydrogen electrode turns out to be the anode, the second electrode has a positive potential (cathode). In the series of metal activities, hydrogen is located between metals with negative and positive standard potentials. Standard electrode potentials, expressed relative to the hydrogen electrode, are given in the tables. We can use the table to find the potentials and calculate the emf of a copper-zinc galvanic cell:
j o (Cu 2+ /Cu) = +0.34 V; j o (Zn 2+ /Zn) = –0.76 V; EMF = 0.34 V – (–0.76 V) = 1.1 V.
Electrochemical potential or μ - physical quantity, connecting the chemical potential (μ) and electrical potential (φ) of some electrochemical system by the relation:
A = μ + e·φ
For the solute:
μ = μ 0 + R*T*lnC + z*F*φ
μ 0 - Standard chemical potential, depending on the nature of the solvent.
C - concentration of the substance
R - gas constant
T - temperature
z - ion valency
F - Faraday number
φ - electric potential
| This is a draft article on thermodynamics and statistical physics. You can help the project by adding to it. |
Write a review about the article "Electrochemical potential"
An excerpt characterizing the Electrochemical potential
- Is it okay, Petrov? - one asked.“Brother, it’s too hot.” Now they won’t interfere,” said another.
- Can't see anything. How they fried it in theirs! Not in sight; darkness, brothers. Would you like to get drunk?
French people last time were repulsed. And again, in complete darkness, Tushin’s guns, surrounded as if by a frame by buzzing infantry, moved somewhere forward.
In the darkness, it was as if an invisible, gloomy river was flowing, all in one direction, humming with whispers, talking and the sounds of hooves and wheels. In the general din, behind all the other sounds, the moans and voices of the wounded in the darkness of the night were clearest of all. Their groans seemed to fill all the darkness that surrounded the troops. Their groans and the darkness of this night were one and the same. After a while, there was a commotion in the moving crowd. Someone rode with his retinue on a white horse and said something as they passed. What did you say? Where to now? Stand, or what? Thank you, or what? - greedy questions were heard from all sides, and the entire moving mass began to push on itself (apparently, the front ones had stopped), and rumors spread that they were ordered to stop. Everyone stopped as they were walking, in the middle of the dirt road.
Let us consider in more detail the mechanism of occurrence of galvanic potentials using the example of a hydrogen electrode. The hydrogen electrode belongs to the electrodes of the first kind. Hydrogen electrode is platinized platinum immersed in an acid solution, such as HC1, and blown with a stream of hydrogen gas. A reaction occurs at the electrode
where H+ q denotes the solvated proton in aqueous solution(i.e. hydronium ion H e O +), and e(Pt) is the electron remaining in the platinum. At such an electrode, a hydrogen molecule dissociates to form a hydronium ion in solution and a conduction electron in platinum. In this case, the metal platinum is charged negatively, and the solution - positively. As a consequence, an electrical potential difference arises between the platinum and the solution. A double layer appears, consisting of negative and positive charges, resembling a flat electric capacitor. The hydrogen electrode is reversible with respect to the cation.
When considering the equilibrium for the given dissociation reaction, it is necessary to take into account that the resulting H + cation, leaving the platinum, does work against electrical forces. This work is done due to the thermal energy of the solution. It is equal to the stored electrical energy. Therefore, the chemical potential of aquated protons, p(H ^ q), will not be equal to the simple sum p°(Hgq) + R71ntf(Hg q), since the solution has an electrical potential different from platinum. Taking into account the work against the electric field forces in the process of proton transfer, for p(H* a) we obtain
where cp(Pt) is the electrical potential of the platinum electrode; (p) is the electric potential of the solution; d(HM - activity of hydrogen cations in solution; F- Faraday number (F= 96485 C/mol); value sr (R)- f(P0 is the galvanic potential at the platinum-solution boundary D^f. The Faraday number arose because chemical potentials are usually calculated per mole, and not per electron. Work against electric field forces P[f(/>) - - f(P0] is accomplished due to the thermal energy of the solution. It is this work that ensures the charging of the electrodes, the discharge of which, when the external circuit is closed, is accompanied by the production of electrical energy.
A quantity of type p(H + q) is called electrochemical potential. Equating the chemical potentials for substances in the left and right sides of reaction (16.1) in equilibrium, we obtain
where p)
