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53-409: The refining of liquids is often accomplished by distillation or fractionation ; this process is useful, for example, for isolating different fractions of petroleum . Gases can be refined in this way as well, by being cooled and/or compressed until they liquefy. Gases and liquids can also be refined by extraction with a selective solvent that dissolves away either the substance of interest, or

106-423: A change in pressure at one point in a liquid is transmitted undiminished to every other part of the liquid and very little energy is lost in the form of compression. However, the negligible compressibility does lead to other phenomena. The banging of pipes, called water hammer , occurs when a valve is suddenly closed, creating a huge pressure-spike at the valve that travels backward through the system at just under

159-422: A fairly constant temperature, making a liquid suitable for blanching , boiling , or frying . Even higher rates of heat transfer can be achieved by condensing a gas into a liquid. At the liquid's boiling point, all of the heat energy is used to cause the phase change from a liquid to a gas, without an accompanying increase in temperature, and is stored as chemical potential energy . When the gas condenses back into

212-403: A given rate, such as when it is being sheared at finite velocity. A specific example is a liquid flowing through a pipe: in this case the liquid undergoes shear deformation since it flows more slowly near the walls of the pipe than near the center. As a result, it exhibits viscous resistance to flow. In order to maintain flow, an external force must be applied, such as a pressure difference between

265-404: A limited degree of particle mobility. As the temperature increases, the increased vibrations of the molecules causes distances between the molecules to increase. When a liquid reaches its boiling point , the cohesive forces that bind the molecules closely together break, and the liquid changes to its gaseous state (unless superheating occurs). If the temperature is decreased, the distances between

318-433: A liquid this excess heat-energy is released at a constant temperature. This phenomenon is used in processes such as steaming . Since liquids often have different boiling points, mixtures or solutions of liquids or gases can typically be separated by distillation , using heat, cold, vacuum , pressure, or other means. Distillation can be found in everything from the production of alcoholic beverages , to oil refineries , to

371-452: A microwave oven. This is due to heating cycles releasing dissolved gases such as oxygen and nitrogen from the solvent. There are ways to prevent superheating in a microwave oven, such as putting a non-metallic object (such as a stir stick) into the container beforehand or using a scratched container. To avoid a dangerous sudden boiling, it is recommended not to microwave water for an excessive amount of time. Superheating of hydrogen liquid

424-451: A mixture of otherwise immiscible liquids can be stabilized to form an emulsion , where one liquid is dispersed throughout the other as microscopic droplets. Usually this requires the presence of a surfactant in order to stabilize the droplets. A familiar example of an emulsion is mayonnaise , which consists of a mixture of water and oil that is stabilized by lecithin , a substance found in egg yolks . The microscopic structure of liquids

477-765: A plane cutting a bubble into two halves. Each half is pulled towards the middle with a surface tension force F ∝ π d {\displaystyle F\propto \pi d} , which must be balanced by the force from excess pressure Δ p × ( π d 2 / 4 ) {\displaystyle \Delta p\times (\pi d^{2}/4)} . So we obtain Δ p ( π d 2 / 4 ) ∝ π d {\displaystyle \Delta p(\pi d^{2}/4)\propto \pi d} , which simplifies to Δ p ∝ d − 1 {\displaystyle \Delta p\propto d^{-1}} . This means if

530-409: A relatively narrow temperature/pressure range to exist. Most known matter in the universe is either gas (as interstellar clouds ) or plasma (as stars ). Liquid is one of the four primary states of matter , with the others being solid, gas and plasma . A liquid is a fluid . Unlike a solid, the molecules in a liquid have a much greater freedom to move. The forces that bind the molecules together in

583-485: A rotating liquid forms a circular paraboloid and can therefore be used as a telescope . These are known as liquid-mirror telescopes . They are significantly cheaper than conventional telescopes, but can only point straight upward ( zenith telescope ). A common choice for the liquid is mercury. Quantities of liquids are measured in units of volume . These include the SI unit cubic metre (m ) and its divisions, in particular

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636-451: A smooth container of purified liquid can reliably superheat. Superheating can occur when an undisturbed container of water is heated in a microwave oven . At the time the container is removed, the lack of nucleation sites prevents boiling, leaving the surface calm. However, once the water is disturbed, some of it violently flashes to steam , potentially spraying boiling water out of the container. The boiling can be triggered by jostling

689-407: A solid are only temporary in a liquid, allowing a liquid to flow while a solid remains rigid. A liquid, like a gas, displays the properties of a fluid. A liquid can flow, assume the shape of a container, and, if placed in a sealed container, will distribute applied pressure evenly to every surface in the container. If liquid is placed in a bag, it can be squeezed into any shape. Unlike a gas, a liquid

742-472: Is a fixed amount of energy associated with forming a surface of a given area. This quantity is a material property called the surface tension , in units of energy per unit area (SI units: J / m ). Liquids with strong intermolecular forces tend to have large surface tensions. A practical implication of surface tension is that liquids tend to minimize their surface area, forming spherical drops and bubbles unless other constraints are present. Surface tension

795-456: Is a so-called metastable state or metastate , where boiling might occur at any time, induced by external or internal effects. Superheating is achieved by heating a homogeneous substance in a clean container, free of nucleation sites , while taking care not to disturb the liquid. This may occur by microwaving water in a very smooth container. Disturbing the water may cause an unsafe eruption of hot water and result in burns . Water

848-440: Is complex and historically has been the subject of intense research and debate. A few of the key ideas are explained below. Microscopically, liquids consist of a dense, disordered packing of molecules. This contrasts with the other two common phases of matter, gases and solids. Although gases are disordered, the molecules are well-separated in space and interact primarily through molecule-molecule collisions. Conversely, although

901-436: Is considered to be a promising candidate for these applications as it is a liquid near room temperature, has low toxicity, and evaporates slowly. Liquids are sometimes used in measuring devices. A thermometer often uses the thermal expansion of liquids, such as mercury , combined with their ability to flow to indicate temperature. A manometer uses the weight of the liquid to indicate air pressure . The free surface of

954-408: Is given by where: For a body of water open to the air, p 0 {\displaystyle p_{0}} would be the atmospheric pressure . Static liquids in uniform gravitational fields also exhibit the phenomenon of buoyancy , where objects immersed in the liquid experience a net force due to the pressure variation with depth. The magnitude of the force is equal to the weight of

1007-437: Is important since machinery often operate over a range of temperatures (see also viscosity index ). The viscous behavior of a liquid can be either Newtonian or non-Newtonian . A Newtonian liquid exhibits a linear strain/stress curve, meaning its viscosity is independent of time, shear rate, or shear-rate history. Examples of Newtonian liquids include water, glycerin , motor oil , honey , or mercury. A non-Newtonian liquid

1060-437: Is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds . Like a gas, a liquid is able to flow and take the shape of a container. Unlike a gas, a liquid maintains a fairly constant density and does not disperse to fill every space of a container. Although liquid water is abundant on Earth, this state of matter is actually the least common in the known universe, because liquids require

1113-451: Is nearly incompressible, meaning that it occupies nearly a constant volume over a wide range of pressures; it does not generally expand to fill available space in a container but forms its own surface, and it may not always mix readily with another liquid. These properties make a liquid suitable for applications such as hydraulics . Liquid particles are bound firmly but not rigidly. They are able to move around one another freely, resulting in

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1166-473: Is no equilibrium at this transition under constant pressure, so unless supercooling occurs, the liquid will eventually completely crystallize. However, this is only true under constant pressure, so that (for example) water and ice in a closed, strong container might reach an equilibrium where both phases coexist. For the opposite transition from solid to liquid, see melting . The phase diagram explains why liquids do not exist in space or any other vacuum. Since

1219-805: Is of vital importance in chemistry and biology, and it is necessary for all known forms of life. Inorganic liquids include water, magma , inorganic nonaqueous solvents and many acids . Important everyday liquids include aqueous solutions like household bleach , other mixtures of different substances such as mineral oil and gasoline, emulsions like vinaigrette or mayonnaise , suspensions like blood, and colloids like paint and milk . Many gases can be liquefied by cooling, producing liquids such as liquid oxygen , liquid nitrogen , liquid hydrogen and liquid helium . Not all gases can be liquified at atmospheric pressure, however. Carbon dioxide , for example, can only be liquified at pressures above 5.1 atm . Some materials cannot be classified within

1272-435: Is one where the viscosity is not independent of these factors and either thickens (increases in viscosity) or thins (decreases in viscosity) under shear. Examples of non-Newtonian liquids include ketchup , custard , or starch solutions. The speed of sound in a liquid is given by c = K / ρ {\displaystyle c={\sqrt {K/\rho }}} where K {\displaystyle K}

1325-447: Is responsible for a range of other phenomena as well, including surface waves , capillary action , wetting , and ripples . In liquids under nanoscale confinement , surface effects can play a dominating role since – compared with a macroscopic sample of liquid – a much greater fraction of molecules are located near a surface. The surface tension of a liquid directly affects its wettability . Most common liquids have tensions ranging in

1378-459: Is said to "boil" when bubbles of water vapor grow without bound, bursting at the surface. For a vapor bubble to expand, the temperature must be high enough that the vapor pressure exceeds the ambient pressure (the atmospheric pressure , primarily). Below that temperature, a water vapor bubble will shrink and vanish. Superheating is an exception to this simple rule; a liquid is sometimes observed not to boil even though its vapor pressure does exceed

1431-530: Is that a larger bubble is easier to inflate than a small one; just as when blowing up a balloon, the hardest part is getting started. It turns out the excess pressure Δ p {\displaystyle \Delta p} due to surface tension is inversely proportional to the diameter d {\displaystyle d} of the bubble. That is, Δ p ∝ d − 1 {\displaystyle \Delta p\propto d^{-1}} . This can be derived by imagining

1484-425: Is the bulk modulus of the liquid and ρ {\displaystyle \rho } the density. As an example, water has a bulk modulus of about 2.2  GPa and a density of 1000 kg/m , which gives c = 1.5 km/s. At a temperature below the boiling point , any matter in liquid form will evaporate until reaching equilibrium with the reverse process of condensation of its vapor. At this point

1537-1247: The cryogenic distillation of gases such as argon , oxygen , nitrogen , neon , or xenon by liquefaction (cooling them below their individual boiling points). Liquid is the primary component of hydraulic systems, which take advantage of Pascal's law to provide fluid power . Devices such as pumps and waterwheels have been used to change liquid motion into mechanical work since ancient times. Oils are forced through hydraulic pumps , which transmit this force to hydraulic cylinders . Hydraulics can be found in many applications, such as automotive brakes and transmissions , heavy equipment , and airplane control systems. Various hydraulic presses are used extensively in repair and manufacturing, for lifting, pressing, clamping and forming. Liquid metals have several properties that are useful in sensing and actuation , particularly their electrical conductivity and ability to transmit forces (incompressibility). As freely flowing substances, liquid metals retain these bulk properties even under extreme deformation. For this reason, they have been proposed for use in soft robots and wearable healthcare devices , which must be able to operate under repeated deformation. The metal gallium

1590-709: The operating temperature range of the component. Oils are often used in engines, gear boxes , metalworking , and hydraulic systems for their good lubrication properties. Many liquids are used as solvents , to dissolve other liquids or solids. Solutions are found in a wide variety of applications, including paints , sealants , and adhesives . Naphtha and acetone are used frequently in industry to clean oil, grease, and tar from parts and machinery. Body fluids are water-based solutions. Surfactants are commonly found in soaps and detergents . Solvents like alcohol are often used as antimicrobials . They are found in cosmetics, inks , and liquid dye lasers . They are used in

1643-478: The ambient pressure. The cause is an additional force, the surface tension , which suppresses the growth of bubbles. Surface tension makes the bubble act like an elastic balloon. The pressure inside is raised slightly by the "skin" attempting to contract. For the bubble to expand, the temperature must be raised slightly above the boiling point to generate enough vapor pressure to overcome both surface tension and ambient pressure. What makes superheating so explosive

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1696-470: The cavities left by the bubbles with tremendous localized force, eroding any adjacent solid surface. In a gravitational field , liquids exert pressure on the sides of a container as well as on anything within the liquid itself. This pressure is transmitted in all directions and increases with depth. If a liquid is at rest in a uniform gravitational field, the pressure p {\displaystyle p} at depth z {\displaystyle z}

1749-459: The classical three states of matter. For example, liquid crystals (used in liquid-crystal displays ) possess both solid-like and liquid-like properties, and belong to their own state of matter distinct from either liquid or solid. Liquids are useful as lubricants due to their ability to form a thin, freely flowing layer between solid materials. Lubricants such as oil are chosen for viscosity and flow characteristics that are suitable throughout

1802-781: The cubic decimeter, more commonly called the litre (1 dm = 1 L = 0.001 m ), and the cubic centimetre, also called millilitre (1 cm = 1 mL = 0.001 L = 10 m ). The volume of a quantity of liquid is fixed by its temperature and pressure . Liquids generally expand when heated, and contract when cooled. Water between 0 °C and 4 °C is a notable exception. On the other hand, liquids have little compressibility . Water, for example, will compress by only 46.4 parts per million for every unit increase in atmospheric pressure (bar). At around 4000 bar (400 megapascals or 58,000 psi ) of pressure at room temperature water experiences only an 11% decrease in volume. Incompressibility makes liquids suitable for transmitting hydraulic power , because

1855-418: The cup, inserting a stirring device, or adding a substance like instant coffee or sugar. The chance of superheating is greater with smooth containers, because scratches or chips can house small pockets of air, which serve as nucleation points. Superheating is more likely after repeated heating and cooling cycles of an undisturbed container, as when a forgotten coffee cup is re-heated without being removed from

1908-443: The ends of the pipe. The viscosity of liquids decreases with increasing temperature. Precise control of viscosity is important in many applications, particularly the lubrication industry. One way to achieve such control is by blending two or more liquids of differing viscosities in precise ratios. In addition, various additives exist which can modulate the temperature-dependence of the viscosity of lubricating oils. This capability

1961-423: The enormous variation seen in other mechanical properties, such as viscosity. The free surface of a liquid is disturbed by gravity ( flatness ) and waves ( surface roughness ). An important physical property characterizing the flow of liquids is viscosity . Intuitively, viscosity describes the resistance of a liquid to flow. More technically, viscosity measures the resistance of a liquid to deformation at

2014-624: The food industry, in processes such as the extraction of vegetable oil . Liquids tend to have better thermal conductivity than gases, and the ability to flow makes a liquid suitable for removing excess heat from mechanical components. The heat can be removed by channeling the liquid through a heat exchanger , such as a radiator , or the heat can be removed with the liquid during evaporation . Water or glycol coolants are used to keep engines from overheating. The coolants used in nuclear reactors include water or liquid metals, such as sodium or bismuth . Liquid propellant films are used to cool

2067-424: The four fundamental states of matter (the others being solid , gas , and plasma ), and is the only state with a definite volume but no fixed shape. The density of a liquid is usually close to that of a solid, and much higher than that of a gas. Therefore, liquid and solid are both termed condensed matter . On the other hand, as liquids and gases share the ability to flow, they are both called fluids. A liquid

2120-477: The individual elements are solid under the same conditions (see eutectic mixture ). An example is the sodium-potassium metal alloy NaK . Other metal alloys that are liquid at room temperature include galinstan , which is a gallium-indium-tin alloy that melts at −19 °C (−2 °F), as well as some amalgams (alloys involving mercury). Pure substances that are liquid under normal conditions include water, ethanol and many other organic solvents. Liquid water

2173-594: The largest bubbles in a container are small, only a few micrometres in diameter, overcoming the surface tension may require a large Δ p {\displaystyle \Delta p} , requiring exceeding the boiling point by several degrees Celsius. Once a bubble does begin to grow, the surface tension pressure decreases, so it expands explosively in a positive feedback loop. In practice, most containers have scratches or other imperfections which trap pockets of air that provide starting bubbles, and impure water containing small particles can also trap air pockets. Only

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2226-416: The liquid displaced by the object, and the direction of the force depends on the average density of the immersed object. If the density is smaller than that of the liquid, the buoyant force points upward and the object floats, whereas if the density is larger , the buoyant force points downward and the object sinks. This is known as Archimedes' principle . Unless the volume of a liquid exactly matches

2279-594: The molecules become smaller. When the liquid reaches its freezing point the molecules will usually lock into a very specific order, called crystallizing, and the bonds between them become more rigid, changing the liquid into its solid state (unless supercooling occurs). Only two elements are liquid at standard conditions for temperature and pressure : mercury and bromine . Four more elements have melting points slightly above room temperature : francium , caesium , gallium and rubidium . In addition, certain mixtures of elements are liquid at room temperature, even if

2332-409: The molecules in solids are densely packed, they usually fall into a regular structure, such as a crystalline lattice ( glasses are a notable exception). Superheating In thermodynamics , superheating (sometimes referred to as boiling retardation , or boiling delay ) is the phenomenon in which a liquid is heated to a temperature higher than its boiling point , without boiling . This

2385-526: The pressure is essentially zero (except on surfaces or interiors of planets and moons) water and other liquids exposed to space will either immediately boil or freeze depending on the temperature. In regions of space near the Earth, water will freeze if the sun is not shining directly on it and vaporize (sublime) as soon as it is in sunlight. If water exists as ice on the Moon, it can only exist in shadowed holes where

2438-460: The speed of sound. Another phenomenon caused by liquid's incompressibility is cavitation . Because liquids have little elasticity they can literally be pulled apart in areas of high turbulence or dramatic change in direction, such as the trailing edge of a boat propeller or a sharp corner in a pipe. A liquid in an area of low pressure (vacuum) vaporizes and forms bubbles, which then collapse as they enter high pressure areas. This causes liquid to fill

2491-629: The sun never shines and where the surrounding rock does not heat it up too much. At some point near the orbit of Saturn, the light from the Sun is too faint to sublime ice to water vapor. This is evident from the longevity of the ice that composes Saturn's rings. Liquids can form solutions with gases, solids, and other liquids. Two liquids are said to be miscible if they can form a solution in any proportion; otherwise they are immiscible. As an example, water and ethanol (drinking alcohol) are miscible whereas water and gasoline are immiscible. In some cases

2544-450: The tens of mJ/m , so droplets of oil, water, or glue can easily merge and adhere to other surfaces, whereas liquid metals such as mercury may have tensions ranging in the hundreds of mJ/m , thus droplets do not combine easily and surfaces may only wet under specific conditions. The surface tensions of common liquids occupy a relatively narrow range of values when exposed to changing conditions such as temperature, which contrasts strongly with

2597-732: The thrust chambers of rockets . In machining , water and oils are used to remove the excess heat generated, which can quickly ruin both the work piece and the tooling. During perspiration , sweat removes heat from the human body by evaporating. In the heating, ventilation, and air-conditioning industry (HVAC), liquids such as water are used to transfer heat from one area to another. Liquids are often used in cooking due to their excellent heat-transfer capabilities. In addition to thermal conduction, liquids transmit energy by convection. In particular, because warmer fluids expand and rise while cooler areas contract and sink, liquids with low kinematic viscosity tend to transfer heat through convection at

2650-480: The unwanted impurities. Many solids can be refined by growing crystals in a solution of the impure material; the regular structure of the crystal tends to favor the desired material and exclude other kinds of particles. Chemical reactions are often used to remove impurities of particular types. The use of silicon and other semiconductors in electronics depends on precise control of impurities. The zone melting process developed by William Gardner Pfann

2703-426: The vapor will condense at the same rate as the liquid evaporates. Thus, a liquid cannot exist permanently if the evaporated liquid is continually removed. A liquid at or above its boiling point will normally boil, though superheating can prevent this in certain circumstances. At a temperature below the freezing point, a liquid will tend to crystallize , changing to its solid form. Unlike the transition to gas, there

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2756-405: The volume of its container, one or more surfaces are observed. The presence of a surface introduces new phenomena which are not present in a bulk liquid. This is because a molecule at a surface possesses bonds with other liquid molecules only on the inner side of the surface, which implies a net force pulling surface molecules inward. Equivalently, this force can be described in terms of energy: there

2809-398: Was used to produce pure germanium , and subsequently float-zone silicon became available when Henry Theuerer of Bell Labs adapted Pfann's method to silicon. Types of materials that are usually refined: Liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a nearly constant volume independent of pressure. It is one of

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