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quantum mechanics | Chemistry | 1 | The study of how atoms, molecules, subatomic particles, etc. behave and are structured. |
quark | Chemistry | 1 | An elementary particle and a fundamental constituent of matter. |
racemate | Chemistry | 1 | An equimolar mixture of a pair of enantiomers which does not exhibit optical activity. The chemical name or formula of a racemate is distinguished from those of the enantiomers by the prefix (±)- or by the symbols RS and SR. |
radiation | Chemistry | 1 | Energy released in the form of waves or subatomic particles when there is a change from high-energy to low-energy states. |
radical | Chemistry | 1 | Any atom, molecule, or ion that has at least one unpaired valence electron. With few exceptions, such unpaired electrons make radicals highly chemically reactive, and therefore organic radicals are usually short-lived. |
radioactive decay | Chemistry | 1 | The process by which an unstable atomic nucleus loses excess nuclear energy by emitting radiation in any of several forms, including as gamma radiation, as alpha or beta particles, or by ejecting electrons from its atomic orbitals. |
radiochemistry | Chemistry | 1 | The branch of chemistry involving the study of radioactive substances and radioactivity, including the use of radioactive isotopes to study non-radioactive isotopes and ordinary chemical reactions. |
radionuclide | Chemistry | 1 | A radioactive nuclide of a specified element, especially a particular isotope of that element which characteristically undergoes spontaneous decay into one or more stable nuclides by emitting excess energy from the nucleus. |
raoult's law | Chemistry | 1 | A law of thermodynamics which states that the partial pressure of each gaseous component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its molar fraction in the mixture. |
rare-earth element | Chemistry | 1 | Any of the 17 nearly indistinguishable, silvery-white, soft, heavy metallic elements belonging to a set including the lanthanide series (atomic numbers 57 through 71) as well as scandium and yttrium. |
rate-determining step | Chemistry | 1 | The slowest step in a chemical reaction that involves more than one step. The rate of this step determines the overall reaction rate. |
reactant | Chemistry | 1 | Any substance that is consumed in the course of a chemical reaction. |
reaction | Chemistry | 1 | See chemical reaction. |
reaction barrier | Chemistry | 1 | The energy deficit that must be overcome in order for a particular chemical reaction to proceed. In transition state theory, the reaction barrier is interpreted as the difference between the zero-point energy of the activated complex formed in the reaction and that of the initial reactants. See also activation energy. |
reaction mechanism | Chemistry | 1 | The step-by-step sequence of elementary reactions by which a larger chemical reaction or overall change occurs. A complete mechanism must describe and explain which bonds are broken and which are formed (and in what order), as well as all reactants, products, and catalysts involved; the amounts of each; all intermediates, activated complexes, and transition states; and the stereochemistry of each chemical species. Because the detailed processes of a complex reaction are not observable in most cases, a reaction mechanism is often a theoretical conjecture based on thermodynamic feasibility and what little support can be gained from experiment. |
reaction rate | Chemistry | 1 | The speed at which reactants are converted into products in a chemical reaction. |
reactive bond | Chemistry | 1 | A chemical bond between atoms which, in a particular context, is relatively unstable and therefore easily broken or invaded by other chemical species or radicals; e.g. the double bond in ethylene (CH2=CH2) is highly reactive in the presence of other ethylene molecules, leading to a polymerization reaction that forms polyethylene. |
reactive intermediate | Chemistry | 1 | Any short-lived, unstable, highly reactive chemical species which is generated briefly in a chemical reaction but rapidly undergoes further reactions that transform it into a more stable species. It is thus a transient intermediary between the stable reactants and products of the overall reaction. The existence of intermediates, when detectable, is critical to an accurate understanding of a reaction mechanism. |
reactivity | Chemistry | 1 | The tendency of a particular chemical substance to undergo a chemical reaction, either by itself or with other substances, generally referring to either or both of two distinct observations: whether or not a substance reacts under a specific set of circumstances, and how quickly it reacts (i.e. the reaction rate). Thermodynamically, a chemical reaction occurs because the products (taken as a group) exist at a lower free energy than the reactants, and hence are more energetically "stable", but the concept of reactivity may also embody kinetic factors, depending on the usage. Chemical stability and chemical compatibility are related but distinct concepts. |
reactivity series | Chemistry | 1 | An empirical, calculated, and structurally analytical progression of a series of metals, arranged by their general reactivity from highest to lowest and used to summarize information about their reactions with acids and water and the methods used to extract them from ores. |
reagent | Chemistry | 1 | A substance used in a laboratory to produce a reaction. |
reducing agent | Chemistry | 1 | A chemical species that loses or donates one or more electrons to another species, called the oxidizing agent, in a redox reaction, thereby causing the reduction of the other species and in turn being itself oxidized. The reducing agent's oxidation state increases, while the oxidizing agent's decreases. |
reduction | Chemistry | 1 | The decrease in the oxidation state of a chemical species in a redox reaction, generally by gaining electrons. Contrast oxidation. |
refractory | Chemistry | 1 | 1. Having a high melting point. |
retort | Chemistry | 1 | A laboratory apparatus used for the distillation or dry distillation of chemical substances, traditionally consisting of a spherical vessel with a long, downward-pointing neck that conducts the condensed vapors produced by distillation into a separate collection vessel. |
reversible reaction | Chemistry | 1 | A chemical reaction that can proceed in either direction depending on the reaction conditions, i.e. from reactants to products or from products to reactants, especially implying one in which both conversions occur simultaneously. Contrast irreversible reaction. |
s-block | Chemistry | 1 | The collective name for the elements in Groups 1 and 2 of the periodic table (the alkali and alkaline metals), as well as hydrogen and helium. |
saline solution | Chemistry | 1 | A common term for a solution of sodium chloride (NaCl) dissolved in water (H2O). |
salt | Chemistry | 1 | In chemistry, a salt is produced when a strong acid and strong base react. Strong acid + strong base = salt + water. |
salt bridge | Chemistry | 1 | A device used to connect reduction with oxidation half-cells in an electrochemical cell. |
schrödinger equation | Chemistry | 1 | A quantum state equation which represents the behaviour of an electron around an atom. |
scintillation | Chemistry | 1 | A burst of luminescence of short duration produced by an individual energetically excited particle as it releases energy. |
semiconductor | Chemistry | 1 | An electrically conductive solid whose degree of conductivity lies somewhere between that of a conductor and that of an insulator. |
side chain | Chemistry | 1 | A chemical substituent group that is attached to the core part or "backbone" of a larger molecule, especially an oligomeric or polymeric hydrocarbon chain that branches off of the longer primary chain of a macromolecule. The term is most commonly encountered in biochemistry and organic chemistry. |
single bond | Chemistry | 1 | A bond that involves the sharing of one pair of electrons. |
sol | Chemistry | 1 | A suspension of solid particles in a liquid. Artificial examples include sol-gels. |
solid | Chemistry | 1 | One of the four fundamental states of matter, characterized by relatively low-energy particles packed closely together in rigid structures with definite shape and volume. See Young's modulus. |
solubility | Chemistry | 1 | The property of a solid, liquid, or gaseous solute to dissolve in a solid, liquid, or gaseous solvent. It is typically expressed as the proportion of solute dissolved in the solvent in a fully saturated solution. |
solubility product | Chemistry | 1 | A measure of the solubility of an ionic solute, expressed as the arithmetic product of the concentrations of its ions in a fully saturated solution, with respect to the solute's particular dissociation equilibria and the particular ions present. For a dissociation equilibrium A x B y ( s ) ⇋ x A ( a q ) + + y B ( a q ) − {\textstyle \mathrm {{A_{x}}{B_{y}}_{(s)}} \leftrightharpoons \mathrm {xA_{(aq)}^{+}} +\mathrm {yB_{(aq)}^{-}} } , the solubility product of the ionic solute A x B y {\textstyle \mathrm {A_{x}} \mathrm {B_{y}} } is given by K s = x y {\textstyle K_{{\ce {s}}}=^{x}^{y}} , where {\textstyle } and {\textstyle } are the concentrations of the solute's ionic constituents in a saturated solution. The solubility product is derived from and functions like the equilibrium constant of dissociation, though unlike an equilibrium constant it is not dimensionless. If the product of ionic concentrations in a solution exceeds the solubility product, then precipitation occurs. |
solute | Chemistry | 1 | The part of a solution that is dissolved into the solvent. For example, sodium chloride (NaCl) is the solute in a solution of saline water. |
solution | Chemistry | 1 | A homogeneous mixture made up of multiple substances generally referred to as solutes and solvents. |
solvation | Chemistry | 1 | Any stabilizing interaction of a solute with a solvent, or a similar interaction between a solvent and groups of an insoluble material (e.g. the ionic groups of an ion-exchange resin). Such interactions generally involve electrostatic forces and van der Waals forces, as well as compound-specific effects such as hydrogen bonding. See also dissolution. |
solvent | Chemistry | 1 | A liquid that dissolves another substance to form a solution. For example, water is a solvent for sugar – when sugar is dissolved in water, it becomes a sugar solution. |
sonication | Chemistry | 1 | The process of irradiating a substance with sound energy, usually at ultrasound (>20 kHz) frequencies, in order to agitate the particles in a sample for various purposes, such as increasing the rate of a chemical reaction or preparing vesicles in mixtures of surfactants and water. |
spatial isomer | Chemistry | 1 | See stereoisomer. |
specific heat capacity | Chemistry | 1 | The heat capacity of a sample of a substance divided by the mass of the sample. Informally, it is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. The SI unit of specific heat capacity is joule per kelvin per kilogram (J/K/kg). Specific heat capacity often varies with temperature and with each state of matter. |
cp | Chemistry | 1 | The heat capacity of a sample of a substance divided by the mass of the sample. Informally, it is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. The SI unit of specific heat capacity is joule per kelvin per kilogram (J/K/kg). Specific heat capacity often varies with temperature and with each state of matter. |
spectrometry | Chemistry | 1 | See mass spectrometry. |
spectroscopy | Chemistry | 1 | The study of radiation and matter, such as X-ray absorption and emission spectroscopy. |
standard conditions of temperature and pressure | Chemistry | 1 | A standardisation of ambient temperature and pressure used in order to easily compare experimental results. Standard temperature is 25 degrees Celsius (°C) and standard pressure is 100.000 kilopascals (kPa). Standard conditions are often denoted with the abbreviation STP or SATP. |
stp | Chemistry | 1 | A standardisation of ambient temperature and pressure used in order to easily compare experimental results. Standard temperature is 25 degrees Celsius (°C) and standard pressure is 100.000 kilopascals (kPa). Standard conditions are often denoted with the abbreviation STP or SATP. |
state of matter | Chemistry | 1 | The condition of matter existing in a distinct, homogeneous, macroscopic form. Solid, liquid, gas, and plasma are the four traditional states of matter and the most well-known. See also phase. |
stereoisomer | Chemistry | 1 | An isomer which possesses an identical chemical composition but which differs in the spatial arrangement of its atoms. |
stoichiometry | Chemistry | 1 | The calculation of quantities of reactants and products in chemical reactions. Stoichiometry is based on the law of conservation of mass and the observation that quantities of reactants and products typically exist in ratios of positive integers, implying that if the amounts of the separate reactants are known, then the amounts of the products can be calculated, and vice versa. |
strong acid | Chemistry | 1 | An acid that completely dissociates in solution according to the reaction HA + S ↽ − − ⇀ SH + + A − {\ce {HA + S <=> SH+ + A-}}} , or to such an extent that the concentration of the undissociated species HA {\ce {HA}}} is too low to be measured. Any acid with a pKa of less than approximately -2 is generally considered a strong acid; an example is hydrochloric acid (HCl). Contrast weak acid. |
structural formula | Chemistry | 1 | A graphical representation of the molecular structure of a compound that shows how the atoms are arranged relative to one another. |
subatomic particle | Chemistry | 1 | Any particle that is smaller than an atom. Examples include protons, neutrons, and electrons. |
sublimation | Chemistry | 1 | The phase transition of a substance from a solid to a limewater fuel or gas without an apparent intervening transition to a liquid in the process. |
substance | Chemistry | 1 | See chemical substance. |
substituent | Chemistry | 1 | An atom or a group of atoms which substitutes or replaces another atom or group of atoms within a larger molecule as the product of a chemical reaction, thereby becoming a moiety of the newly formed compound, generally without causing any significant change to other parts of the same molecule. For example, a hydroxyl group may be substituted for any of the hydrogen atoms in benzene to form phenol. See also side chain and functional group. |
substitution reaction | Chemistry | 1 | A type of chemical reaction in which one functional group or substituent within a larger compound replaces or is substituted for another functional group or substituent. |
superheavy elements | Chemistry | 1 | See transactinides. |
surfactant | Chemistry | 1 | A chemical wetting agent that reduces the surface tension between oil and water. Detergents and soaps are surfactants. |
suspension | Chemistry | 1 | A heterogeneous mixture that contains solid particles which are sufficiently large for sedimentation to occur, by which such particles separate from and settle out of the fluid over time if left undisturbed. In a suspension, the solute does not dissolve but remains dispersed or suspended throughout the fluid solvent only transiently and with mechanical agitation. Contrast colloid and solution. |
tarnish | Chemistry | 1 | A thin layer of corrosion that forms on the surface of copper, brass, aluminum, magnesium, and other soft metals or alloys as their outermost layer undergoes a chemical reaction with the surrounding air, often but not necessarily involving atmospheric oxygen. Tarnish usually appears as a dull grey, black, or sometimes iridescent film or coating on the metal. It is a self-limiting surface phenomenon, as the tarnished top layers of the metal protect underlying layers from reacting. |
temperature | Chemistry | 1 | A proportional measure of the average kinetic energy of the random motions of the constituent microscopic particles of a system. The SI unit for temperature is the kelvin. |
ternary compound | Chemistry | 1 | A chemical compound containing three different elements. |
terpene | Chemistry | 1 | A class of naturally occurring unsaturated hydrocarbons with carbon skeletons derived from one or more units of isoprene (C5H8). Terpenes are often subclassified according to the total number of carbon atoms they contain, e.g. the C5 hemiterpenes, C10 monoterpenes, C20 diterpenes, etc. |
theoretical yield | Chemistry | 1 | See yield. |
thermal conductivity | Chemistry | 1 | The property of a material that allows it to conduct thermal energy or heat (a quantity often denoted by k k} ). |
thermochemistry | Chemistry | 1 | The study of the absorption or release of heat during a chemical reaction. |
thermodynamic stability | Chemistry | 1 | The condition of a system being in its lowest energy state with its environment (equilibrium). |
thermodynamics | Chemistry | 1 | The study of the effects of changing temperature, volume, or pressure (or work, heat, and energy) on a macroscopic scale. |
thermometer | Chemistry | 1 | An instrument used to measure temperature. |
thiol | Chemistry | 1 | 1. Any of a class of organosulfur compounds consisting of a sulfur atom attached to a hydrogen atom and any other organic substituent, with the general formula R–SH. Thiols are the sulfur analogues of alcohols. Also thiol derivative and mercaptan. |
titration | Chemistry | 1 | A laboratory method of quantitative chemical analysis that is used to determine the concentration of an identified analyte. The procedure involves preparing a particular reagent as a standard solution of known concentration and volume (called the titrant or titrator) and allowing it to react with a solution of the analyte (called the titrand) to determine the latter's concentration. |
torr | Chemistry | 1 | A unit for measuring pressure, equivalent to 133.322 Pa or 1.3158 × 10−3 atm. |
trace element | Chemistry | 1 | An element in a sample which has an average concentration of less than 100 parts per million atoms or less than 100 micrograms per gram. |
transactinides | Chemistry | 1 | In the periodic table, the set of chemical elements with an atomic number greater than 103, i.e. those heavier than the actinides. The transactinides are a subset of the transuranic elements. |
transition metal | Chemistry | 1 | An element whose atoms naturally occur with incompletely filled "d" sub-shells. These elements are grouped as the so-called d-block elements in the periodic table. |
transuranic elements | Chemistry | 1 | The set of chemical elements with an atomic number greater than 92, i.e. occurring after uranium in the periodic table. None of the transuranic elements are stable in naturally occurring conditions. |
triple bond | Chemistry | 1 | A bond that involves the covalent sharing of three pairs of electrons (for example, the diatomic nitrogen molecule, N2, is composed of two nitrogen atoms linked by a triple bond). |
triple point | Chemistry | 1 | The place where temperature and pressure of three phases are the same. Water has a special phase diagram. |
tyndall effect | Chemistry | 1 | The effect of light scattering by colloidal or suspended particles. |
un number | Chemistry | 1 | A four-digit code used to note hazardous and flammable substances. |
uncertainty | Chemistry | 1 | The notion that any measurement that involves estimation of any amount cannot be exactly reproducible. |
uncertainty principle | Chemistry | 1 | Knowing the location of a particle makes the momentum uncertain, while knowing the momentum of a particle makes the location uncertain. |
unit cell | Chemistry | 1 | The smallest repeating unit of a crystalline lattice. |
unit factor | Chemistry | 1 | Statements used in converting between units. |
vacuum flask | Chemistry | 1 | A storage vessel consisting of two flasks or other containers, placed one within the other and joined at the neck, and a space in between that is partially evacuated of air, creating a near-vacuum that significantly reduces the transfer of heat between the vessel's interior and its ambient environment. Vacuum flasks can greatly lengthen the time over which their contents remain warmer or cooler than the ambient environment. |
valence electron | Chemistry | 1 | Any of the outermost electrons of an atom, which are located in electron shells. |
valence bond theory | Chemistry | 1 | A theory explaining the chemical bonding within molecules by discussing valencies, the number of chemical bonds formed by an atom. |
valency | Chemistry | 1 | The combining capacity of an element. |
van der waals force | Chemistry | 1 | One of the forces (attraction/repulsion) between molecules. |
van 't hoff factor | Chemistry | 1 | The ratio of moles of particles in solution to moles of solute dissolved. |
vapor | Chemistry | 1 | When a substance is below the critical temperature while in the gas phase. |
vapor pressure | Chemistry | 1 | The pressure exerted by a vapor which is in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. It is commonly described as the tendency of particles to spontaneously escape from the liquid or solid state into the gaseous state and is used as an indication of a liquid's evaporation rate. |
vaporization | Chemistry | 1 | The phase transition of a substance from a liquid to a gas. |
vaporization point | Chemistry | 1 | See boiling point. |
viscosity | Chemistry | 1 | A measure of the resistance of a liquid to flow. |
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