Chemistry Dictionary Terminology "E"

Chemistry Dictionary

Terminology "E"

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Effective Collisons

Collision between molecules resulting in a reaction; one in which the molecules collide with proper relative orientations and sufficient energy to react.

Effective Molality

The sum of the molalities of all solute particles in a solution.

Effective Nuclear Charge

The nuclear charge experienced by the outermost electrons of an atom; the actual nuclear charge minus the effects of shielding due to inner-shell electrons.

Example: Set of dx₂-y₂ and dz₂ orbitals; those d orbitals within a set with lobes directed along the x-, y-, and z-axes.

Electrical Conductivity

Ability to conduct electricity.

Electrochemistry

Study of chemical changes produced by electrical current and the production of electricity by chemical reactions.

Electrodes

Surfaces upon which oxidation and reduction half-reactions; occur in electrochemical cells.

Electrode Potentials

Potentials, E, of half-reactions as reductions versus the standard hydrogen electrode.

Electrolysis

Process that occurs in electrolytic cells.

Electrolyte

A substance whose aqueous solutions conduct electricity.

Electrolytic Cells

Electrochemical cells in which electrical energy causes nospontaneous redox reactions to occur.

An electrochemical cell in which chemical reactions are forced to occur by the application of an outside source of electrical energy.

Electrolytic Conduction

Conduction of electrical current by ions through a solution or pure liquid.

Electromagnetic Radiation

Energy that is propagated by means of electric and magnetic fields that oscillate in directions perpendicular to the direction of travel of the energy.

Electromotive Series

The relative order of tendencies for elements and their simple ions to act as oxidizing or reducing agents; also called the activity series.

Electron

A subatomic particle having a mass of 0.00054858 amu and a charge of 1-.

Electron Affinity

The amount of energy absorbed in the process in which an electron is added to a neutral isolated gaseous atom to form a gaseous ion with a 1- charge; has a negative value if energy is released.

Electron Configuration

Specific distribution of electrons in atomic orbitals of atoms or ions.

Electron Deficient Compounds

Compounds that contain at least one atom (other than H) that shares fewer than eight electrons

Electronic Transition

The transfer of an electron from one energy level to another.

Electronegativity

A measure of the relative tendency of an atom to attract electrons to itself when chemically combined with another atom.

Electronic Geometry

The geometric arrangement of orbitals containing the shared and unshared electron pairs surrounding the central atom of a molecule or polyatomic ion.

Electrophile

Positively charged or electron-deficient.

Electrophoresis

A technique for separation of ions by rate and direction of migration in an electric field.

Electroplating

Plating a metal onto a (cathodic) surface by electrolysis.

Element

A substance that cannot be decomposed into simpler substances by chemical means.

Eluant or eluent

The solvent used in the process of elution, as in liquid chromatography.

Eluate

Solvent (or mobile phase) which passes through a chromatographic column and removes the sample components from the stationary phase.

Emission Spectrum

Spectrum associated with emission of electromagnetic radiation by atoms (or other species) resulting from electronic transitions from higher to lower energy states.

Emulsifying Agent

A sustance that coats the particles of the dispersed phase and prevents coagulation of colloidal particles; an emulsifier.

Emulsion

Colloidal suspension of a liquid in a liquid.

Enantiomer

One of the two mirror-image forms of an optically active molecule.

Endothermic

Describes processes that absorb heat energy.

Endothermicity

The absorption of heat by a system as the process occurs.

End Point

The point at which an indicator changes colour and a titration is stopped.

Energy

The capacity to do work or transfer heat.

Enthalpy

The heat content of a specific amount of substance; defined as E= PV.

Entropy

A thermodynamic state or property that measures the degree of disorder or randomness of a system.

For more information see Thermochemistry

Enzyme

A protein that acts as a catalyst in biological systems.

Equation of State

An equation that describes the behavior of matter in a given state; the van der Waals equation describes the behavior of the gaseous state.

Equilibrium or Chemical Equilibrium

A state of dynamic balance in which the rates of forward and reverse reactions are equal; the state of a system when neither forward or reverse reaction is thermodynamically favored.

Equilibrium Constant

A quantity that characterizes the position of equilibrium for a reversible reaction; its magnitude is equal to the mass action expression at equilibrium. K varies with temperature.

Equivalence Point

The point at which chemically equivalent amounts of reactants have reacted.

Equivalent Weight

An oxidizing or reducing agent, who's mass gains (oxidizing agents) or loses (reducing agents) 6.022 x 10²³ electrons in a redox reaction.

The mass of an acid or base that furnishes or reacts with 6.022 x 10²³ H₃O+ or OH- ions.

Essential Oil

A plant extract that has a distinctive odour or flavour.

Ester

A Compound of the general formula R-C-O-R1 where R and R1 may be the same or different, and may be either aliphatic or aromatic.

Ether

Compound in which an oxygen atom is bonded to two alkyl or two aryl groups, or one alkyl and one aryl group.

Eutrophication

The undesirable overgrowth of vegetation caused by high concentrates of plant nutrients in bodies of water.

Evaporization

Vaporization of a liquid below its boiling point.

Evaporation Rate

The rate at which a particular substance will vapourize (evaporate) when compared to the rate of a known substance such as ethyl ether. This term is especially useful for health and fire-hazard considerations.

Excited State

Any state other than the ground state of an atom or molecule.

Exothermic

Describes processes that release heat energy.

Exothermicity

The release of heat by a system as a process occurs.

Explosive

A chemical or compound that causes a sudden, almost instantaneous release or pressure, gas, heat and light when subjected to sudden shock, pressure, high temperature or applied potential.

Explosive limits

The range of concentrations over which a flammable vapour mixed with proper ratios of air will ignite or explode if a source of ignitions is provided.

Extensive Property

A property that depends upon the amount of material in a sample.

Extrapolate

To estimate the value of a result outside the range of a series of known values. Technique used in standard additions calibration procedure.