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Entropy
Entropy (S) is a measure of the unavailability of a system's energy to do work; in a closed system, an increase in entropy is accompanied by a decrease in energy availability. When a system undergoes a reversible change the entropy (S) changes by an amount equal to the energy (Q) transferred to the system by heat divided by the thermodynamic temperature (T) at which this occurs.
ΔS=ΔQ/T
All real processes are to a certain extent irreversible changes and in any closed system an irreversible change is always accompanied by an increase in entropy.

Enzyme
Enzyme is a protein that acts as a catalyst in biochemical reactions. Each enzyme is specific to a particular reaction or group of similar reactions. Many require the association of certain nonprotein cofactors in order to function. The molecule undergoing reaction (the substrate) binds to a specific active site on the enzyme molecule to form a short-lived intermediate: this greatly increases (by a factor of up to 1020) the rate at which the reaction proceeds to form the product.

Epoxy resin
Epoxy resins are thermosetting resins produced by copolymerising epoxide compounds with phenols (e.g. epichlorohydrin and bisphenol A). They contain ether linkages (-O-) and form a tight, cross-linked polymer network. Toughness, good adhesion, corrosive-chemical resistance, and good dielectric properties characterize epoxy resins. Most epoxy resins are two-part type which harden when blended.

Equation of state
Equation of state is an equation relating the pressure, volume, and temperature of a substance or system. Equation of state for ideal gas
pV = nRT
where p is pressure, V molar volume, T temperature, and R the molar gas constant (8.314 JK-1mol-1).

Erg
Erg (erg) is a non-SI (cgs) unit of energy, equal to 10-7 J.

Esters
A volatile fruity odoured product of the reaction between a carboxylic acid and an alcohol. Esters are organic compounds formed by reaction between alcohol and acids. Esters formed from carboxylic acids have the general formula RCOOR'. Triesters, molecules containing three ester groups, occur in nature as oils and fats.

Ethers
Ethers are organic compounds with formula R-O-R, where R is not equal to H. They may be derived from alcohols by elimination of water, but the major method is catalytic hydration of olefins. They are volatile highly flammable compounds; when containing peroxides they can detonate on heating. The term ether is often used synonymously with ethyl ether.

Euler number
Euler number (Eu) is a dimensionless quantity used in fluid mechanics, defined by
Eu=Δp/ρ•ν²
where p is pressure, ρ is density, and v is velocity.

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Eutectic
Eutectic is a solid solution consisting of two or more substances and having the lowest freezing point of any possible mixture of these components.
Eutectic point is the lowest temperature at which the eutectic mixture can exist in liquid phase. A liquid having the eutectic composition will freeze at a single temperature without change of composition.

Exothermic reaction
The majority of chemical reactions are accompanied by the evolution of heat - these is known as exothermic reactions. The reaction between an acid and a base is exothermic, it is possible to feel the temperature change when one is added to the other - see below: A rapid exothermic reation results in an explosion, as occurs when TNT explodes. Fatty acid
A naturally occuring, usually in fats, monobasic carboxylic acid, with a long hydrocarbon tail chains.

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F
Ferromagnetism
Many substances are found to be magnetic, in that they are attracted by magnetic and electric fields, but it is found that the metals iron, cobalt, nickel and a number of alloys posses a greater level of magnetism than other substances. This powerful magnetism is called ferromagnetism, and is due to a large magnetic moment in the atoms of the metals due to an unbalanced spin of the electrons in their inner orbits.

F block
The lanthanides and actinides, elements in which the f atomic orbitals are being filled.

Face-centered cubic
A lattice structure having atoms in the center of each face and at each corner of a cube, abbreviated fcc.

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Fahrenheit
The temperature scale defined by the values 32 °F for the freezing point of water and 212 °F for the boiling point of water.

Family
Those elements that comprise a single column of the periodic table.

Faraday
The charge associated with a mole of electrons, 96,485 C/mol.

Faraday constant
The electric charge carried by one mole of electrons, 9.648 670 x 104 C mol-1; abbreviated F.

Faraday's law
The proportionality between the number of moles of a substance produced or consumed in an electrochemical cell and the amount of electricity that passes through the electrical circuit of the cell.

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Fat
A molecule that is an ester of glycerol and three fatty acids.

Fatty acid
A long-chain carboxylic acid that is a component of the triglycerides which constitute fat.

Fcc
Abbreviation for face-centered cubic; a lattice structure having atoms in the center of each face and at each corner of a cube.

Ferromagnetic
Able to acquire a permanent magnetization.

Filtration
The process of separating a solid from a liquid by permitting the liquid to pass through a filter.

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First law of thermodynamics
A formal statement of the conservation of energy as applied to chemical systems; the change in internal energy is equal to the sum of the heat added to a system plus the work done to the system.

First-order reaction
A reaction for which the rate is directly proportional to the concentration of one reactant.

Fission
A nuclear reaction in which large nuclei break apart to form smaller ones.

Fluorescence
The slow emission of longer wavelength light following the absorption of shorter wavelength radiation. Fluorescence is common with aromatic compounds with several rings joined together. Phosphorescence is similar but may persist long after the stimulating radiation is extinguished.

Formal charge
A quantity useful for predicting reactivity patterns of molecules. Its value is found by dividing bonding electrons equally between bonded atoms and calculating the resulting charge on each atom.

Formation constant
An equilibrium constant for a reaction in which a product of interest is formed; often applied to the formation of a complex ion from the central metal ion and ligands.

Formula weight
The mass of one mole of a formula unit of a substance; molar mass.

Free energy
A thermodynamic function corresponding to the tendency for spontaneous change in a system; represented by the symbol G.

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Freezing
The process of forming a solid from a liquid.

Freezing point
The temperature at which a liquid becomes a solid; also called melting point.

Freezing point depression
The decrease in the freezing point of a liquid as a result of the presence of a solute.

Frequency
The rate at which a periodic event occurs; specifically, the rate at which the waves of electromagnetic radiation pass a point.

Fuel cell
An electrochemical cell in which the reactants are supplied on a continuing basis.

Functional group
A set of atoms in a molecule that confer on the molecule a characteristic set of physical and chemical properties.

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Fusion
A nuclear reaction in which small nuclei are united to form larger ones.

G
Gamma rays
One of the three types of rays produced by radioactive disintegration, but gamma rays are the only one comprised of electromagnetic radiation. Gamma rays have a very short wavelength, and have the greatest penetrative power of all radioactive emissions.

Glycols
Glycols are compounds that have two hydroxyl groups present in each molecule. The simplest member is ethylene glycol - see below:

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H
Halogens
This important group of elements occupies Group VII of the periodic table. Its first element, fluorine, is the most strongly electronegative element known. All halogens are electron defficient and readily share electrons with other elements to staisfy their valency needs, eg. they all form compounds with hydrogen, with the formula HX (where X=halogen)

Heavy water
A molecule of water contains two atoms of hydrogen and one of oxygen. Most water comprises of hydrogen/oxygen but a small percentage is composed of another hydrogen isotope, deuterium and oxygen. Deuterium differs from hydrogen by having one neutron in the nucleus of each atom. Deuterium water is given the formula D2O. There is approx. 1 part in 5000 D2O in normal water and it can be concentrated by electrolysis. D2O had a higher boiling point (101.4 °C) and melts at 3.6 °C

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Heterocyclic molecule
A molecule containing at least one ring of carbon atoms, and which also has at least one atom from a different element, (nitrogen, sulphur, oxygen etc..) within the ring. Examples are shown below:

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Hydrocarbon
A molecule comprised solely of carbon and hydrogen. The simplest example is Methane. Hydrogen bond
A bond formed by a hydrogen atom to an electronegative atom, and is denoted X---H-B.

Hydrogen ion
The ion which is left when the hydrogen atom loses its electron, forming a proton. In water the hydrogen ion binds to the water molecules, producing H3O+. Compound which exhibit hydrogen bonding include water and amines.

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I
Indicators
A number of complex organic molecules can change their molecular structure and colour when faced with different pH conditions. The most well known indicator is litmus, which is a mixture of vegetable dyes. A list of common synthetic dyes is given below:

Infrared radiation
Electromagnetic radiation whose wavelength is longer than that of visible light, and is responsible for the transmission of radiant heat.

Ion
An electrically charged atom or group of atoms. If an atom or molecule gains an electron - it becomes a negatively charged anion, or if it loses an electron it becomes a positively charged cation.

Isomerism
If a molecule possesses the same molecular formula, but the atoms are arranged in a different way, then they are called isomers. Isomers have different physical and chemical properties from each other. Optically active isomers differ only in the fact one is the mirror image of the other, as shown with lactic acid below:

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Many isomers occur as a result of different substituents occupying different positions on a benzene ring - see below:

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Isotactic
Means geometrically regular. A polymer is isotactic if all of the groups attched to the back bone are arranged in the same geometrical pattern.

Isotopes
All atoms of the same element posses the same no. of protons and electrons but not neccarily the same no. of neutrons. So all atoms of an element will react in the same way, but they can differ in their molecular masses. Atoms of the same element with different masses are known as isotopes. Hydrogen has three isotopes. 99.98% of all hydrogen has one proton and one electron, while 0.02% of hydrogen has one proton, one neutron and one electron. This isotope is called deuterium. There is also a trace of a third isotope, tritium, which has two neutrons in its nucleus.

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K
Kelvin
Kelvin (K) is the SI base unit of thermodynamic temperature. The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The unit is named after the British scientist Sir. W. Thompson, Lord Kelvin (1824-1907).

Ketone
An organic compound containing the carbonyl group, >C=O, to which other carbon atoms are attached. Ketones are extremely useful as solvents and paint components. An example is Butanedione.

Kilogram
Kilogram (kg) is the SI base unit of mass; it is equal to the mass of the international prototype of the kilogram.
The prototype of the standard is a cylinder of platinum-iridium alloy, 39 mm in diameter and 39 mm high. Prototype of the kilogram kept by the Bureau International des Poids et Mesures (International Bureau of Weights and Measures) at S?evres, near Paris.

Kjeldhal flask
Kjeldhal flask is a round bottom flask with a long wide neck that is used in the determination of nitrogen by Kjeldhal's method.

Kjeldhal's method
Kjeldhal's method is an analytical method for determination of nitrogen in certain organic compounds. The method was developed by the Danish chemist Johan Kjeldahl (1849-1900).
It involves addition of a small amount of anhydrous potassium sulfate to the test compound, followed by heating mixture with concentrated sulfuric acid, often with a catalyst such as copper sulfate. As a result ammonia is formed. After alkalyzing the mixture with sodium hydroxyde, the ammonia is separated by distilation, collected in standard acid, and the nitrogen determined by back-titration.

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Knudsen number
Knudsen number (Kn) is a dimensionless quantity used in fluid mechanics, defined by
Kn = λ/l
where λ is mean free path and l is length.

Kohlrausch's law
If a salt is dissolved in water, the conductivity of the solution is the sum of the conductances of the anions and cations. The law, which depends on the independent migration of ions, was deduced experimentally by German chemist Friedrich Kohlrausch (1840-1910).

L
laminar flow
Laminar flow is smooth, uniform, non-turbulent flow of a gas or liquid in parallel layers, with little mixing between layers. It is characterized by small values of the Reynolds number.

Lanthanides
Lanthanides (lanthanons, lanthanoids or rare-earth elements) are a series of fourteen elements in the periodic table, generally considered to range in proton number from cerium to lutetium inclusive. It was convenient to divide these elements into the cerium group or light earth: cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu); and the yttrium group or heavy earths: gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) i lutetium (Lu). The position of lanthanum is somewhat equivocal and, although not itself a lanthanides, it is often included with them for comparative purpose. The lanthanides are sometimes simply called the rare earths. Apart from unstable Pm the lanthanides are actually not rare. Cerium is the 26. most abundant of all elements, 5 times as abundant as Pb. All are silvery very reactive metals.
This is a group of fifteen closely related elements and are known as the rare earth or "inner transition" elements. They are so alike that they are difficult to seperate from each other and usually all occur together in nature.

Laser
Laser (light amplification by stimulated emission of radiation) is a light amplifier usually used to produce monochromatic coherent radiation in the infrared, visible, and ultraviolet regions of the electromagnetic spectrum.

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Latent heat
Latent Heat (L) is the quantity of heat absorbed or released when a substance changes its physical phase at constant temperature (e.g. from solid to liquid at the melting point or from liquid to gas at the boiling point).

Lattice constants
Lattice constants are parameters specifying the dimensions of a unit cell in a crystal lattice, specifically the lengths of the cell edges and the angles between them.

Lattice energy
Lattice energy is the energy per ion pair required to separate completely the ions in a crystal lattice at a temperature of absolute zero.

Le Chatelier's principle
The idea that a system at equilibrium will respond to a stress placed upon it in such a manner as to partially offset that stress. The principle was first stated in 1888 by French physical chemist Henri Le Chatelier (1850-1936).

Lewis acid
Lewis acid is an agent capable of accepoting a pair of electrons to form a coordinate bond.

Lewis base
Lewis base is an agent capable of donating a pair of electrons to form a coordinate bond.

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Ligand
Ligand is an ion (F-, Cl-, Br-, I-, S2-, CN-, NCS-, OH-, NH2-) or molecule (NH3, H2O, NO, CO) that donates a pair of electron to a metal atom or ion in forming a coordination complex.

Ligand field theory
Ligand field theory is a description of the structure of crystals containing a transition metal ion surrounded by nonmetallic ions (ligands). It is based on construction of molecular orbitals involving the d-orbitals of the central metal ion and combinations of atomic orbitals of the ligands.

Light year
Light year (ly) is a unit of distance used in astronomy, defined as the distance light travels in one year in a vacuum (ly = 9.46052973∙1015).

Lignins
Lignins are macromolecular constituents of wood related to lignans, composed of phenolic propylbenzene skeletal units, linked at various sites and apparently randomly.

Lipid
A naturally occurring substance soluble in organic solvents but not in water. Lipids are a loosely defined term for substances of biological origin that are soluble in nonpolar solvents. They consist of saponifiable lipids, such as glycerides (fats and oils) and phospholipids, as well as nonsaponifiable lipids, principally steroids.

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Liter
Liter (l, L) is a synonym for cubic decimeter (L = dm3).

Lithosphere
Lithosphere is the outer layer of the solid earth, extending from the base of the mantle to the surface of the crust.

Lone pair
A pair of electrons not involved in bond formation.

LPG
LPG (Liquid Petroleum Gas) is a mixture of short hydrocarbons with most of the volume being propane and butane. LPG is considered an alternative fuel that burns cleaner than gasoline.

Lumen
Lumen (lm) is the SI derived unit of luminous flux. The lumen is the luminous flux emitted in a solid angle of one steradian by a point source having a uniform intensity of one candela (1lm =1 cd∙sr).

Luminous flux
Luminous flux (Φ) is the intensity of light from a source multiplied by the solid angle. The SI unit is lumen.

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Lux
Lux (lx) is the SI derived unit of illuminance. The lux is the illuminance produced by a luminous flux of one lumen uniformly distributed over a surface of one square metre (lx = lm•m-2).

Lyman series
Lyman series is the series of lines in the spectrum of the hydrogen atom which corresponds to transitions between the ground state (principal quantum number n = 1) and successive excited states.

M
Molecule
A molecule is two or more atoms joined together by chemical bonds. This may result in two atoms of the same molecule, such as chlorine, Cl2, or by combining elements as in ammonia, NH3. A molecule can be considered the smallest unit representitve of that compound which possesses all its properties.

Monomer
A monomer is a starting material or single unit from which a polymer is built. It refers to the repeat units that make up the polymer chains. Ethylene is the monomer for polyethylene and styrene for polystyrene.

N
Neutron
One of the three fundamental particles which form atoms, the neutron has the mass of a proton but no electrical charge. Neutrons are emitted when large atomic nuclei are bombarded with alpha particles.