In thermodynamics, chemical potential of a species is energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition. The chemical potential of a species in a mixture is defined as the rate of change of a free energy of a thermodynamic system with respect to the change in the number of atoms or molecules of the species that are added to the system. Thus, it is the partial derivative of the free energy with respect to the amount of the species, all other species' concentrations in the mixture remaining constant; the molar chemical potential is known as partial molar free energy. When both temperature and pressure are held constant, chemical potential is the partial molar Gibbs free energy. At chemical equilibrium or in phase equilibrium the total sum of the product of chemical potentials and stoichiometric coefficients is zero, as the free energy is at a minimum. In semiconductor physics, the chemical potential of a system of electrons at a temperature of zero Kelvin is known as the Fermi energy.
Particles tend to move from higher chemical potential to lower chemical potential. In this way, chemical potential is a generalization of "potentials" in physics such as gravitational potential; when a ball rolls down a hill, it is moving from a higher gravitational potential to a lower gravitational potential. In the same way, as molecules move, dissolve, etc. they will always tend to go from a higher chemical potential to a lower one, changing the particle number, conjugate variable to chemical potential. A simple example is a system of dilute molecules diffusing in a homogeneous environment. In this system, the molecules tend to move from areas with high concentration to low concentration, until the concentration is the same everywhere; the microscopic explanation for this is based in the random motion of molecules. However, it is simpler to describe the process in terms of chemical potentials: For a given temperature, a molecule has a higher chemical potential in a higher-concentration area, a lower chemical potential in a low concentration area.
Movement of molecules from higher chemical potential to lower chemical potential is accompanied by a release of free energy. Therefore, it is a spontaneous process. Another example, not based on concentration but on phase, is a glass of liquid water with ice cubes in it. Above 0 °C, an H2O molecule, in the liquid phase has a lower chemical potential than a water molecule, in the solid phase; when some of the ice melts, H2O molecules convert from solid to liquid where their chemical potential is lower, so the ice cubes shrink. Below 0 °C, the molecules in the ice phase have the lower chemical potential, so the ice cubes grow. At the temperature of the melting point, 0 °C, the chemical potentials in water and ice are the same. A third example is illustrated by the chemical reaction of dissociation of a weak acid HA: HA ⇌ H+ + A−Vinegar contains acetic acid; when acid molecules dissociate, the concentration of the undissociated acid molecules decreases and the concentrations of the product ions increase.
Thus the chemical potential of HA decreases and the sum of the chemical potentials of H+ and A− increases. When the sums of chemical potential of reactants and products are equal the system is at equilibrium and there is no tendency for the reaction to proceed in either the forward or backward direction; this explains why vinegar is acidic, because acetic acid dissociates to some extent, releasing hydrogen ions into the solution. Chemical potentials are important in many aspects of equilibrium chemistry, including melting, evaporation, osmosis, partition coefficient, liquid-liquid extraction and chromatography. In each case there is a characteristic constant, a function of the chemical potentials of the species at equilibrium. In electrochemistry, ions do not always tend to go from higher to lower chemical potential, but they do always go from higher to lower electrochemical potential; the electrochemical potential characterizes all of the influences on an ion's motion, while the chemical potential includes everything except the electric force.
The chemical potential μi of species i is defined, as all intensive quantities are, by the phenomenological fundamental equation of thermodynamics expressed in the form, which holds for both reversible and irreversible processes d U = T d S − P d V + ∑ i = 1 n μ i d N i,where dU is the infinitesimal change of internal energy U, dS the infinitesimal change of entropy S, dV is the infinitesimal change of volume V for a thermodynamic system in thermal equilibrium, dNi is the infinitesimal change of particle number Ni of species i as particles are added or subtracted. T is absolute temperature, S is entropy, P is pressure, V is volume. Other work terms, such as those involving electric, magnetic or gravitational fields may be added. From the above equation the chemical potential is given by μ i =
A solvent is a substance that dissolves a solute, resulting in a solution. A solvent is a liquid but can be a solid, a gas, or a supercritical fluid; the quantity of solute that can dissolve in a specific volume of solvent varies with temperature. Common uses for organic solvents are in dry cleaning, as paint thinners, as nail polish removers and glue solvents, in spot removers, in detergents and in perfumes. Water is a solvent for the most common solvent used by living things. Solvents find various applications in chemical, pharmaceutical and gas industries, including in chemical syntheses and purification processes; when one substance is dissolved into another, a solution is formed. This is opposed to the situation. In a solution, all of the ingredients are uniformly distributed at a molecular level and no residue remains. A solvent-solute mixture consists of a single phase with all solute molecules occurring as solvates, as opposed to separate continuous phases as in suspensions and other types of non-solution mixtures.
The ability of one compound to be dissolved in another is known as solubility. In addition to mixing, the substances in a solution interact with each other at the molecular level; when something is dissolved, molecules of the solvent arrange around molecules of the solute. Heat transfer is involved and entropy is increased making the solution more thermodynamically stable than the solute and solvent separately; this arrangement is mediated by the respective chemical properties of the solvent and solute, such as hydrogen bonding, dipole moment and polarizability. Solvation does not cause a chemical chemical configuration changes in the solute. However, solvation resembles a coordination complex formation reaction with considerable energetics and is thus far from a neutral process. Solvents can be broadly classified into two categories: non-polar. A special case is mercury; the dielectric constant of the solvent provides a rough measure of a solvent's polarity. The strong polarity of water is indicated by its high dielectric constant of 88.
Solvents with a dielectric constant of less than 15 are considered to be nonpolar. The dielectric constant measures the solvent's tendency to cancel the field strength of the electric field of a charged particle immersed in it; this reduction is compared to the field strength of the charged particle in a vacuum. Heuristically, the dielectric constant of a solvent can be thought of as its ability to reduce the solute's effective internal charge; the dielectric constant of a solvent is an acceptable predictor of the solvent's ability to dissolve common ionic compounds, such as salts. Dielectric constants are not the only measure of polarity; because solvents are used by chemists to carry out chemical reactions or observe chemical and biological phenomena, more specific measures of polarity are required. Most of these measures are sensitive to chemical structure; the Grunwald–Winstein mY scale measures polarity in terms of solvent influence on buildup of positive charge of a solute during a chemical reaction.
Kosower's Z scale measures polarity in terms of the influence of the solvent on UV-absorption maxima of a salt pyridinium iodide or the pyridinium zwitterion. Donor number and donor acceptor scale measures polarity in terms of how a solvent interacts with specific substances, like a strong Lewis acid or a strong Lewis base; the Hildebrand parameter is the square root of cohesive energy density. It can not accommodate complex chemistry. Reichardt's dye, a solvatochromic dye that changes color in response to polarity, gives a scale of ET values. ET is the transition energy between the ground state and the lowest excited state in kcal/mol, identifies the dye. Another correlated scale can be defined with Nile red; the polarity, dipole moment and hydrogen bonding of a solvent determines what type of compounds it is able to dissolve and with what other solvents or liquid compounds it is miscible. Polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best: "like dissolves like".
Polar compounds like sugars or ionic compounds, like inorganic salts dissolve only in polar solvents like water, while non-polar compounds like oils or waxes dissolve only in non-polar organic solvents like hexane. Water and hexane are not miscible with each other and will separate into two layers after being shaken well. Polarity can be separated to different contributions. For example, the Kamlet-Taft parameters are dipolarity/polarizability, hydrogen-bonding acidity and hydrogen-bonding basicity; these can be calculated from the wavelength shifts of 3–6 different solvatochromic dyes in the solvent including Reichardt's dye and diethylnitroaniline. Another option, Hansen's parameters, separate the cohesive energy density into dispersion and hydrogen bonding contributions. Solvents with a dielectric constant (more relative
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough and sometimes rigid, it provides the cell with both structural support and protection, acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae and fungi but in other eukaryotes including animals. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters; the composition of cell walls varies between species and may depend on cell type and developmental stage. The primary cell wall of land plants is composed of the polysaccharides cellulose and pectin. Other polymers such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess cell walls made of glycoproteins and polysaccharides such as carrageenan and agar that are absent from land plants. In bacteria, the cell wall is composed of peptidoglycan; the cell walls of archaea have various compositions, may be formed of glycoprotein S-layers, pseudopeptidoglycan, or polysaccharides.
Fungi possess cell walls made of the N-acetylglucosamine polymer chitin. Unusually, diatoms have a cell wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665. However, "the dead excrusion product of the living protoplast" was forgotten, for three centuries, being the subject of scientific interest as a resource for industrial processing or in relation to animal or human health. In 1804, Karl Rudolphi and J. H. F. Link proved. Before, it had been thought that fluid passed between them this way; the mode of formation of the cell wall was controversial in the 19th century. Hugo von Mohl advocated the idea. Carl Nägeli believed that the growth of the wall in thickness and in area was due to a process termed intussusception; each theory was improved in the following decades: the apposition theory by Eduard Strasburger, the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the "living" symplast from the "dead" plant region, the latter of which included the cell wall.
By the 1980s, some authors suggested replacing the term "cell wall" as it was used for plants, with the more precise term "extracellular matrix", as used for animal cells, but others preferred the older term. Cell walls serve similar purposes in those organisms, they may give cells offering protection against mechanical stress. In multicellular organisms, they permit the organism to hold a definite shape. Cell walls limit the entry of large molecules that may be toxic to the cell, they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition and form may change during the cell cycle and depend on growth conditions. In most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength; the apparent rigidity of primary plant tissues is enabled by cell walls, but is not due to the walls' stiffness. Hydraulic turgor pressure creates this rigidity, along with the wall structure.
The flexibility of the cell walls is seen when plants wilt, so that the stems and leaves begin to droop, or in seaweeds that bend in water currents. As John Howland explains Think of the cell wall as a wicker basket in which a balloon has been inflated so that it exerts pressure from the inside; such a basket is rigid and resistant to mechanical damage. Thus does the prokaryote cell gain strength from a flexible plasma membrane pressing against a rigid cell wall; the apparent rigidity of the cell wall thus results from inflation of the cell contained within. This inflation is a result of the passive uptake of water. In plants, a secondary cell wall is a thicker additional layer of cellulose which increases wall rigidity. Additional layers may be formed by suberin in cork cell walls; these compounds are rigid and waterproof. Both wood and bark cells of trees have secondary walls. Other parts of plants such as the leaf stalk may acquire similar reinforcement to resist the strain of physical forces.
The primary cell wall of most plant cells is permeable to small molecules including small proteins, with size exclusion estimated to be 30-60 kDa. The pH is an important factor governing the transport of molecules through cell walls. Cell walls evolved independently including within the photosynthetic eukaryotes. In these lineages, the cell wall is related to the evolution of multicellularity, terrestrialization and vascularization; the walls of plant cells must have sufficient tensile strength to withstand internal osmotic pressures of several times atmospheric pressure that result from the difference in solute concentration between the cell interior and external solutions. Plant cell walls vary from 0.1 to several µm in thickness. Up to three strata or layers may be found in plant cell walls: The primary cell wall a thin and extensible layer formed while the cell is growing; the secondary cell wall, a thick layer formed inside the primary cell wall after the cell is grown. It is not found in all cell types.
Some cells, such as the conducting cells in xylem, possess a secondary wall containing lignin, which strengthens and waterproofs the wall. The middle lamella, a layer rich in pectins; this outermost layer
In statistical mechanics, entropy is an extensive property of a thermodynamic system. It is related to the number Ω of microscopic configurations that are consistent with the macroscopic quantities that characterize the system. Under the assumption that each microstate is probable, the entropy S is the natural logarithm of the number of microstates, multiplied by the Boltzmann constant kB. Formally, S = k B ln Ω. Macroscopic systems have a large number Ω of possible microscopic configurations. For example, the entropy of an ideal gas is proportional to the number of gas molecules N. Twenty liters of gas at room temperature and atmospheric pressure has N ≈ 6×1023. At equilibrium, each of the Ω ≈ eN configurations can be regarded as random and likely; the second law of thermodynamics states. Such systems spontaneously evolve towards the state with maximum entropy. Non-isolated systems may lose entropy, provided their environment's entropy increases by at least that amount so that the total entropy increases.
Entropy is a function of the state of the system, so the change in entropy of a system is determined by its initial and final states. In the idealization that a process is reversible, the entropy does not change, while irreversible processes always increase the total entropy; because it is determined by the number of random microstates, entropy is related to the amount of additional information needed to specify the exact physical state of a system, given its macroscopic specification. For this reason, it is said that entropy is an expression of the disorder, or randomness of a system, or of the lack of information about it; the concept of entropy plays a central role in information theory. Boltzmann's constant, therefore entropy, have dimensions of energy divided by temperature, which has a unit of joules per kelvin in the International System of Units; the entropy of a substance is given as an intensive property—either entropy per unit mass or entropy per unit amount of substance. The French mathematician Lazare Carnot proposed in his 1803 paper Fundamental Principles of Equilibrium and Movement that in any machine the accelerations and shocks of the moving parts represent losses of moment of activity.
In other words, in any natural process there exists an inherent tendency towards the dissipation of useful energy. Building on this work, in 1824 Lazare's son Sadi Carnot published Reflections on the Motive Power of Fire which posited that in all heat-engines, whenever "caloric" falls through a temperature difference, work or motive power can be produced from the actions of its fall from a hot to cold body, he made the analogy with that of. This was an early insight into the second law of thermodynamics. Carnot based his views of heat on the early 18th century "Newtonian hypothesis" that both heat and light were types of indestructible forms of matter, which are attracted and repelled by other matter, on the contemporary views of Count Rumford who showed that heat could be created by friction as when cannon bores are machined. Carnot reasoned that if the body of the working substance, such as a body of steam, is returned to its original state at the end of a complete engine cycle, that "no change occurs in the condition of the working body".
The first law of thermodynamics, deduced from the heat-friction experiments of James Joule in 1843, expresses the concept of energy, its conservation in all processes. In the 1850s and 1860s, German physicist Rudolf Clausius objected to the supposition that no change occurs in the working body, gave this "change" a mathematical interpretation by questioning the nature of the inherent loss of usable heat when work is done, e.g. heat produced by friction. Clausius described entropy as the transformation-content, i.e. dissipative energy use, of a thermodynamic system or working body of chemical species during a change of state. This was in contrast to earlier views, based on the theories of Isaac Newton, that heat was an indestructible particle that had mass. Scientists such as Ludwig Boltzmann, Josiah Willard Gibbs, James Clerk Maxwell gave entropy a statistical basis. In 1877 Boltzmann visualized a probabilistic way to measure the entropy of an ensemble of ideal gas particles, in which he defined entropy to be proportional to the natural logarithm of the number of microstates such a gas could occupy.
Henceforth, the essential problem in statistical thermodynamics, i.e. according to Erwin Schrödinger, has been to determine the distribution of a given amount of energy E over N identical systems. Carathéodory linked entropy with a mathematical definition of irreversibility, in terms of trajectories and integrability. There are two related definitions of entropy: the thermodynamic definition and the statistical mechanics definition; the classical thermodynamics definition developed first. In the classical thermodynamics viewpoint, the system is composed of large numbers of constituents and the state of the system is described by the average thermodynamic properties of those constituents.
The cell is the basic structural and biological unit of all known living organisms. A cell is the smallest unit of life. Cells are called the "building blocks of life"; the study of cells is called cellular biology. Cells consist of cytoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Organisms can be classified as multicellular; the number of cells in plants and animals varies from species to species, it has been estimated that humans contain somewhere around 40 trillion cells. Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometres. Cells were discovered by Robert Hooke in 1665, who named them for their resemblance to cells inhabited by Christian monks in a monastery. Cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, that all cells come from pre-existing cells.
Cells emerged on Earth at least 3.5 billion years ago. Cells are of two types: eukaryotic, which contain a nucleus, prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular. Prokaryotes include two of the three domains of life. Prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling, they are simpler and smaller than eukaryotic cells, lack membrane-bound organelles such as a nucleus. The DNA of a prokaryotic cell consists of a single chromosome, in direct contact with the cytoplasm; the nuclear region in the cytoplasm is called the nucleoid. Most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 µm in diameter. A prokaryotic cell has three architectural regions: Enclosing the cell is the cell envelope – consisting of a plasma membrane covered by a cell wall which, for some bacteria, may be further covered by a third layer called a capsule.
Though most prokaryotes have both a cell membrane and a cell wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, serving as a protective filter; the cell wall consists of peptidoglycan in bacteria, acts as an additional barrier against exterior forces. It prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment; some eukaryotic cells have a cell wall. Inside the cell is the cytoplasmic region that contains the genome and various sorts of inclusions; the genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are circular. Linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. Though not forming a nucleus, the DNA is condensed in a nucleoid.
Plasmids encode additional genes, such as antibiotic resistance genes. On the outside and pili project from the cell's surface; these are structures made of proteins that facilitate communication between cells. Plants, fungi, slime moulds and algae are all eukaryotic; these cells are about fifteen times wider than a typical prokaryote and can be as much as a thousand times greater in volume. The main distinguishing feature of eukaryotes as compared to prokaryotes is compartmentalization: the presence of membrane-bound organelles in which specific activities take place. Most important among these is a cell nucleus, an organelle that houses the cell's DNA; this nucleus gives the eukaryote its name, which means "true kernel". Other differences include: The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls may not be present; the eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are associated with histone proteins.
All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles such as mitochondria contain some DNA. Many eukaryotic cells are ciliated with primary cilia. Primary cilia play important roles in chemosensation and thermosensation. Cilia may thus be "viewed as a sensory cellular antennae that coordinates a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation." Motile eukaryotes can move using motile flagella. Motile cells are absent in flowering plants. Eukaryotic flagella are more complex than those of prokaryotes. All cells, whether prokaryotic or eukaryotic, have a membrane that envelops the cell, regulates what moves in and out, maintains the electric potential of the cell. Inside the membrane, the cytoplasm takes up most of the cell's volume. All cells possess DNA, the hereditary material of genes, RNA, containing the information necessary to build various proteins such as enzymes, the cell's primary machinery.
There are other kinds of biomolecules in cells. This article lists these primary cellular components briefly
Jacobus Henricus van 't Hoff
Jacobus Henricus "Henry" van't Hoff, Jr. was a Dutch physical chemist. A influential theoretical chemist of his time, van't Hoff was the first winner of the Nobel Prize in Chemistry, his pioneering work helped found the modern theory of chemical affinity, chemical equilibrium, chemical kinetics, chemical thermodynamics. In his 1874 pamphlet van't Hoff formulated the theory of the tetrahedral carbon atom and laid the foundations of stereochemistry. In 1875, he predicted the correct structures of allenes and cumulenes as well as their axial chirality, he is widely considered one of the founders of physical chemistry as the discipline is known today. The third of seven children, van't Hoff was born in Rotterdam, Netherlands, 30 August 1852, his father was Jacobus Henricus van't Hoff, Sr. a physician, his mother was Alida Kolff van't Hoff. From a young age, he was interested in science and nature, took part in botanical excursions. In his early school years, he showed a strong interest in philosophy.
He considered Lord Byron to be his idol. Against the wishes of his father, van't Hoff chose to study chemistry. First, he enrolled at Delft University of Technology in September 1869, studied until 1871, when he passed his final exam on 8 July and obtained a degree of chemical technologist, he passed all his courses in two years. He enrolled at University of Leiden to study chemistry, he studied in Bonn, with Friedrich Kekulé and in Paris with C. A. Wurtz, he received his doctorate under Eduard Mulder at the University of Utrecht in 1874. In 1878, van't Hoff married Johanna Francina Mees, they had two daughters, Johanna Francina and Aleida Jacoba, two sons, Jacobus Henricus van't Hoff III and Govert Jacob. Van't Hoff died on 1 March 1911, at Steglitz, near Berlin, of tuberculosis. Van't Hoff earned his earliest reputation in the field of organic chemistry. In 1874, he accounted for the phenomenon of optical activity by assuming that the chemical bonds between carbon atoms and their neighbors were directed towards the corners of a regular tetrahedron.
This three-dimensional structure accounted for the isomers found in nature. He shares credit for this with the French chemist Joseph Le Bel, who independently came up with the same idea. Three months before his doctoral degree was awarded, van't Hoff published this theory, which today is regarded as the foundation of stereochemistry, first in a Dutch pamphlet in the fall of 1874, in the following May in a small French book entitled La chimie dans l'espace. A German translation appeared in 1877, at a time when the only job van't Hoff could find was at the Veterinary School in Utrecht. In these early years his theory was ignored by the scientific community, was criticized by one prominent chemist, Hermann Kolbe. Kolbe wrote: "A Dr. J. H. van ’t Hoff of the Veterinary School at Utrecht has no liking for exact chemical investigation. He has considered it more convenient to mount Pegasus and to proclaim in his ‘La chimie dans l’espace’ how, in his bold flight to the top of the chemical Parnassus, the atoms appeared to him to be arranged in cosmic space."
However, by about 1880 support for van't Hoff's theory by such important chemists as Johannes Wislicenus and Viktor Meyer brought recognition. In 1884, van't Hoff published his research on chemical kinetics, titled Études de Dynamique chimique, in which he described a new method for determining the order of a reaction using graphics and applied the laws of thermodynamics to chemical equilibria, he introduced the modern concept of chemical affinity. In 1886, he showed a similarity between the behaviour of dilute gases. In 1887, he and German chemist Wilhelm Ostwald founded an influential scientific magazine named Zeitschrift für physikalische Chemie, he worked on Svante Arrhenius's theory of the dissociation of electrolytes and in 1889 provided physical justification for the Arrhenius equation. In 1896, he became a professor at the Prussian Academy of Sciences in Berlin, his studies of the salt deposits at Stassfurt were an important contribution to Prussia's chemical industry. Van't Hoff became a lecturer in physics at the Veterinary College in Utrecht.
He worked as a professor of chemistry and geology at the University of Amsterdam for 18 years before becoming the chairman of the chemistry department. In 1896, van't Hoff moved to Germany, where he finished his career at the University of Berlin in 1911. In 1901, he received the first Nobel Prize in Chemistry for his work with solutions, his work showed that dilute solutions follow mathematical laws that resemble the laws describing the behavior of gases. In 1885, van't Hoff was appointed as a member of the Royal Netherlands Academy of Sciences. Other distinctions include honorary doctorates from Harvard and Yale, Victoria University, the University of Manchester, University of Heidelberg, he was awarded the Davy Medal of the Royal Society in 1893, elected a Foreign Member of the Royal Society in 1897. He was awarded the Helmholtz Medal of the Prussian Academy of Sciences and appointed Chevalier de la Légion d'honneur and Senator der Kaiser-Wilhelm-Gesellschaft. Van't Hoff became an honorary member of the British Chemical Society in London, the Royal Dutch Academy of Sciences, American Chemical Society, Borlase's Chemistry Society.
And the Académie des Scienc
Desalination is a process that takes away mineral components from saline water. More desalination refers to the removal of salts and minerals from a target substance, as in soil desalination, an issue for agriculture. Saltwater is desalinated to produce water suitable for human irrigation. One by-product of desalination is salt. Desalination is used on many seagoing submarines. Most of the modern interest in desalination is focused on cost-effective provision of fresh water for human use. Along with recycled wastewater, it is one of the few rainfall-independent water sources. Due to its energy consumption, desalinating sea water is more costly than fresh water from rivers or groundwater, water recycling and water conservation. However, these alternatives are not always available and depletion of reserves is a critical problem worldwide. Desalination processes are either driven by either thermal or electrical as the primary energy types. 1% of the world's population is dependent on desalinated water to meet daily needs, but the UN expects that 14% of the world's population will encounter water scarcity by 2025.
Desalination is relevant in dry countries such as Australia, which traditionally have relied on collecting rainfall behind dams for water. According to the International Desalination Association, in June 2015, 18,426 desalination plants operated worldwide, producing 86.8 million cubic meters per day, providing water for 300 million people. This number increased from 78.4 million cubic meters in a 10.71 % increase in 2 years. The single largest desalination project is Ras Al-Khair in Saudi Arabia, which produced 1,025,000 cubic meters per day in 2014. Kuwait produces a higher proportion of its water than any other country, totaling 100% of its water use. There are several methods; each has advantages and disadvantages but all are useful. The traditional process of desalination is distillation, i.e. boiling and re-condensation of seawater to leave salt and impurities behind. Solar distillation mimics the natural water cycle, in which the sun heats the sea water enough for evaporation to occur. After evaporation, the water vapor is condensed onto a cool surface..
There are two types of solar desalination. The former one is using photo voltaic cells which converts solar energy to electrical energy to power the desalination process; the one utilises the solar energy in the heat form itself and is known as solar thermal powered desalination. In vacuum distillation atmospheric pressure is reduced, thus lowering the temperature required to evaporate the water. Liquids boil when the vapor pressure equals the ambient pressure and vapor pressure increases with temperature. Liquids boil at a lower temperature, when the ambient atmospheric pressure is less than usual atmospheric pressure. Thus, because of the reduced pressure, low-temperature "waste" heat from electrical power generation or industrial processes can be employed. Water is evaporated and separated from sea water through multi-stage flash distillation, a series of flash evaporations; each subsequent flash process utilizes energy released from the condensation of the water vapor from the previous step.
Multiple-effect distillation works through a series of steps called "effects". Incoming water is sprayed onto pipes which are heated to generate steam; the steam is used to heat the next batch of incoming sea water. To increase efficiency, the steam used to heat the sea water can be taken from nearby power plants. Although this method is the most thermodynamically efficient among methods powered by heat, a few limitations exist such as a max temperature and max number of effects. Vapor-compression evaporation involves using either a mechanical compressor or a jet stream to compress the vapor present above the liquid; the compressed vapor is used to provide the heat needed for the evaporation of the rest of the sea water. Since this system only requires power, it is more cost effective; the leading process for desalination in terms of installed capacity and yearly growth is reverse osmosis. The RO membrane processes use semipermeable membranes and applied pressure to preferentially induce water permeation through the membrane while rejecting salts.
Reverse osmosis plant membrane systems use less energy than thermal desalination processes. Energy cost in desalination processes varies depending on water salinity, plant size and process type. At present the cost of seawater desalination, for example, is higher than traditional water sources, but it is expected that costs will continue to decrease with technology improvements that include, but are not limited to, improved efficiency, reduction in plants footprint, improvements to plant operation and optimization, more effective feed pretreatment, lower cost energy sources. Reverse osmosis uses a thin-film composite membrane, which comprises an ultra-thin, aromatic polyamide thin-film; this polyamide film gives the membrane its transport properties, whereas the remainder of the thin-film composite membrane provides mechanical support. The polyamide film is a dense, void-free polymer with a high surface area, allowing for its high water permeability; the Reverse Osmosis process is not maintenance free.
Various factors interfere with efficiency: ionic contamination. In extreme cases the RO membranes are destroyed. To mitigate damage, various pretreatment stages are introduced. Anti-scaling inhibitors include acids and other agents like the organic polymers Polyacrylamide and Polymaleic Acid, Ph