Effective Collisions
Effective collisions are molecular collisions that result in a chemical reaction, occurring when the colliding particles possess sufficient energy (at or above the activation energ…
Chemical Glossary — Letter E
112 chemicals found starting with "E"
Effective Collisions
Collisions between reactant molecules that result in a chemical reaction. For a collision to be effective, molecules must meet two criteria: sufficient energy (at least equal to th…
Effective Molality
Effective molality accounts for the actual number of particles produced when a solute dissolves, by multiplying the nominal molality (m) by the van't Hoff factor (i). For electroly…
Effective Nuclear Charge
Effective nuclear charge (Z_eff) is the net positive charge experienced by an electron in a multi-electron atom, after accounting for the shielding (screening) effect of other elec…
Efflorescence
The process by which a hydrated salt loses its water of crystallization to the atmosphere, resulting in a powdery surface coating. Washing soda (Na₂CO₃·10H₂O) effloresces in dry ai…
Einsteinium
Einsteinium is a synthetic radioactive actinide named after Albert Einstein. It was first identified in the debris of the first hydrogen bomb test (Ivy Mike) in 1952. Only nanogram…
Electrical Conductivity
Electrical conductivity (κ) is the measure of a material's ability to conduct electric current. It is the reciprocal of electrical resistivity (ρ). In solutions, conductivity depen…
Electrochemical Cell
A device that either converts chemical energy into electrical energy (galvanic cell) or uses electrical energy to drive a chemical reaction (electrolytic cell). All electrochemical…
Electrochemical Series
Also known as the activity series or electromotive series, this is a list of elements arranged in order of their standard electrode potentials. It predicts the direction of redox r…
Electrochemistry
The branch of chemistry concerned with the relationship between chemical changes and electrical energy. It encompasses the study of electrochemical cells, electrolysis, electrode p…
Electrochemistry
Electrochemistry is the branch of chemistry that studies the relationship between electrical energy and chemical reactions. It encompasses both the generation of electricity from s…
Electrode
An electrical conductor through which current enters or leaves an electrolytic medium. The anode is the electrode at which oxidation occurs, while the cathode is where reduction oc…
Electrode Potential
The potential difference between an electrode and the electrolyte solution, measured relative to a standard reference electrode. The standard hydrogen electrode (SHE) is assigned a…
Electrode Potentials
Electrode potential is the electromotive force of a galvanic cell built from a standard reference electrode (the standard hydrogen electrode) and another electrode to be characteri…
Electrodes
An electrode is an electrical conductor through which current enters or leaves an electrolytic or galvanic cell. The anode is the electrode where oxidation occurs (loss of electron…
Electrolysis
The process of using electrical energy to drive a non-spontaneous chemical reaction. During electrolysis, oxidation occurs at the anode and reduction at the cathode. Applications i…
Electrolysis
Electrolysis is the process by which an electric current is passed through a substance (usually a liquid electrolyte) to drive a non-spontaneous chemical reaction. In an electrolyt…
Electrolyte
A substance that dissociates into ions when dissolved in water or when melted, allowing the solution to conduct electricity. Strong electrolytes (strong acids, strong bases, solubl…
Electrolyte
An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent such as water. The dissolved electrolyte separates into cations an…
Electrolytic Cell
An electrochemical cell that uses electrical energy to drive a non-spontaneous chemical reaction (electrolysis). The power supply forces electrons to flow in the reverse direction …
Electrolytic Cells
An electrolytic cell is an electrochemical cell that uses electrical energy from an external source to drive a non-spontaneous chemical reaction. This process, called electrolysis,…
Electrolytic Conduction
Electrolytic conduction is the conduction of electric current through an electrolyte solution (or molten electrolyte) by the movement of ions toward electrodes of opposite charge. …
Electromagnetic Radiation
Electromagnetic radiation is a form of energy that propagates through space as oscillating electric and magnetic fields. It spans the electromagnetic spectrum from radio waves (lon…
Electromotive Force (EMF)
The maximum potential difference between the electrodes of a galvanic cell when no current flows, measured in volts. EMF represents the driving force for electron flow in an electr…
Electromotive Series
The electromotive series, also known as the activity series or electrochemical series, is a ranking of elements (usually metals) in order of their standard electrode potentials. El…
Electron
An electron is a subatomic particle with a negative elementary charge (−1.602×10⁻¹⁹ C) and a mass approximately 1/1836 that of a proton. Electrons occupy orbitals around the atomic…
Electron
A subatomic particle with a negative charge of -1.6 × 10⁻¹⁹ coulombs and a mass of 9.11 × 10⁻³¹ kg. Electrons occupy orbitals around the nucleus and are responsible for chemical bo…
Electron Affinity
Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gaseous state to form a negative ion. A more negative electron affinity indica…
Electron Affinity
The energy change when a neutral gaseous atom gains an electron to form a negative ion. Elements with high electron affinity (like halogens) readily accept electrons. Generally inc…
Electron Configuration
Electron configuration describes the distribution of electrons in an atom among its atomic orbitals. Electrons fill orbitals in order of increasing energy following the Aufbau prin…
Electron Configuration
The distribution of electrons in an atom among its atomic orbitals, following the Aufbau principle, Pauli exclusion principle, and Hund's rule. Written using orbital notation (e.g.…
Electron Pair Repulsion
The basis of VSEPR theory, which states that electron pairs around a central atom arrange themselves to minimize repulsion. Lone pairs repel more strongly than bonding pairs, influ…
Electron-Deficient Compounds
Electron-deficient compounds are molecules or ions that have fewer than the expected number of electrons for a complete octet around the central atom. They act as Lewis acids (elec…
Electronegativity
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons toward itself in a covalent bond. The Pauling scale is the most widely used, with f…
Electronegativity
A measure of an atom's ability to attract shared electrons toward itself in a covalent bond. The Pauling scale is most commonly used. Fluorine has the highest electronegativity (4.…
Electronic Configuration
The arrangement of electrons in an atom's orbitals, specifying the number of electrons in each subshell. Determined by Aufbau principle, Pauli exclusion principle, and Hund's rule.…
Electronic Geometry
Electronic geometry (also called electron geometry) describes the arrangement of all electron pairs (bonding pairs AND lone pairs) around a central atom in a molecule. It differs f…
Electronic Transition
An electronic transition is the movement of an electron from one energy level (orbital) to another, occurring through absorption or emission of a photon. The energy of the photon e…
Electrophile
An electrophile is a chemical species that is attracted to electrons and accepts an electron pair to form a new covalent bond. Electrophiles are Lewis acids: they are electron-defi…
Electrophile
An electron-deficient species that is attracted to regions of high electron density and accepts electron pairs in chemical reactions. Examples include carbocations, Lewis acids, an…
Electrophoresis
Electrophoresis is a technique used to separate charged particles (ions, molecules, or cells) by their migration through a medium under the influence of an applied electric field. …
Electrophoresis
The migration of charged particles or molecules through a medium under the influence of an electric field. Widely used in biochemistry to separate DNA, RNA, and proteins by size. G…
Electroplating
Electroplating is the process of depositing a thin layer of metal onto a conductive surface using electrolysis. The object to be coated acts as the cathode, the plating metal acts …
Electroplating
The process of depositing a thin layer of metal onto a surface by electrolysis. The object to be plated is made the cathode, and the plating metal is the anode. Used to improve app…
Electrovalent Bond
Another name for an ionic bond, formed by the complete transfer of electrons from one atom to another. The resulting ions are held together by electrostatic attraction. Also called…
Element
A chemical element is a pure substance that consists of only one type of atom, characterised by the number of protons in its nucleus (atomic number). Elements cannot be broken down…
Element
A pure substance consisting of only one type of atom, characterized by its atomic number (number of protons). Elements cannot be broken down by ordinary chemical means. There are 1…
Elementary Step
An individual step in a reaction mechanism that occurs in a single event at the molecular level. Elementary steps involve one, two, or rarely three molecules colliding simultaneous…
Eluate
The eluate is the solution that exits from a chromatographic column, containing the separated components of the original mixture dissolved in the eluent. In preparative chromatogra…
Eluent
An eluent (also spelled eluant) is the solvent or mobile phase used in chromatography to carry solutes through the stationary phase and cause their separation. The choice of eluent…
Emission Spectrum
An emission spectrum is the characteristic spectrum of electromagnetic radiation emitted by a substance when its atoms or molecules transition from higher to lower energy states. E…
Emission Spectrum
The spectrum of light emitted by an excited element as electrons fall from higher to lower energy levels. Each element produces a unique set of spectral lines (fingerprint). Emissi…
Empirical Formula
The simplest whole-number ratio of atoms of each element in a compound. It shows the relative proportions of elements but not the actual number of atoms. For example, glucose (C₆H₁…
Empirical Formula Mass
The sum of the atomic masses of all atoms in the empirical formula of a compound. Comparing the empirical formula mass to the molar mass of the compound allows calculation of the m…
Emulsifying Agent
An emulsifying agent (emulsifier) is a substance that stabilises an emulsion by reducing interfacial tension between two immiscible liquids (usually oil and water). Emulsifiers hav…
Emulsion
An emulsion is a colloid consisting of two immiscible liquid phases, typically oil and water, where one liquid is dispersed as fine droplets within the other. Emulsions are stabili…
Emulsion
A colloid consisting of two immiscible liquids, one dispersed as droplets within the other. Emulsions require emulsifying agents (emulsifiers) to maintain stability. Milk is an oil…
Enantiomer
Enantiomers are pairs of stereoisomers that are non-superimposable mirror images of each other, differing only in the spatial arrangement of atoms around one or more chiral centers…
Enantiomers
Stereoisomers that are non-superimposable mirror images of each other. They have identical physical and chemical properties in achiral environments but differ in their rotation of …
End Point
The end point (or endpoint) of a titration is the point at which the indicator changes colour, signalling that the reaction between the titrant and the analyte is approximately com…
End Point
The point in a titration at which a visible change, usually a color change of an indicator, signals that the reaction is complete. The end point ideally coincides with the equivale…
Endothermic
An endothermic process is one in which a system absorbs heat energy from its surroundings, resulting in a positive enthalpy change (ΔH > 0). Examples include the melting of ice, th…
Endothermic Reaction
A chemical reaction that absorbs heat energy from the surroundings, causing the temperature of the surroundings to decrease. The enthalpy change (ΔH) is positive. Examples include …
Endothermicity
Endothermicity refers to the property of a reaction or process that absorbs heat from the surroundings. An endothermic reaction has a positive enthalpy change (ΔH > 0), meaning the…
Energetics
The study of energy changes associated with chemical reactions and physical processes. It encompasses thermochemistry, thermodynamics, and the principles governing heat flow, work,…
Energy
Energy is the capacity to do work or transfer heat. In chemistry, it appears in many forms: chemical energy (stored in bonds), thermal energy (heat), kinetic energy (motion), poten…
Energy Level
A specific, discrete amount of energy that an electron can possess in an atom. Electrons occupy quantized energy levels and can only transition between them by absorbing or emittin…
Enthalpy
Enthalpy (H) is a thermodynamic quantity equal to the internal energy of a system plus the product of its pressure and volume (H = U + PV). The change in enthalpy (ΔH) at constant …
Enthalpy
A thermodynamic state function representing the total heat content of a system at constant pressure, defined as H = U + PV. Changes in enthalpy (ΔH) measure the heat released or ab…
Enthalpy of Combustion
The heat released when one mole of a substance undergoes complete combustion in excess oxygen under standard conditions. Always negative (exothermic). Used to compare energy conten…
Enthalpy of Fusion
The heat energy required to convert one mole of a solid into a liquid at its melting point, at constant pressure. Also called latent heat of fusion. It reflects the energy needed t…
Enthalpy of Neutralisation
The heat released when one mole of water is formed by the reaction of an acid with a base under standard conditions. For strong acid-strong base reactions, this value is approximat…
Enthalpy of Solution
The heat change when one mole of a solute dissolves in a large excess of solvent at constant pressure and temperature. It combines the lattice enthalpy of the solute and the hydrat…
Entropy
Entropy (S) is a thermodynamic state function that measures the degree of disorder or randomness in a system. According to the second law of thermodynamics, the total entropy of th…
Entropy
A thermodynamic property measuring the degree of disorder or randomness in a system, symbol S. According to the second law of thermodynamics, entropy of an isolated system tends to…
Enzyme
An enzyme is a biological catalyst, typically a protein, that increases the rate of a biochemical reaction by lowering the activation energy without being consumed. Enzymes are hig…
Enzyme
A biological catalyst, typically a protein, that accelerates chemical reactions in living organisms without being consumed. Enzymes are highly specific, each catalyzing a particula…
Equation of Reaction
A symbolic representation of a chemical reaction showing the reactants, products, and their relative amounts using chemical formulas and coefficients. A balanced equation obeys the…
Equation Of State
An equation of state is a thermodynamic equation relating state variables that describe the state of matter under a given set of physical conditions. The most well-known is the ide…
Equations of State
Mathematical relationships describing the state of matter by relating thermodynamic variables such as pressure, volume, and temperature. The ideal gas law (PV = nRT) is the simples…
Equilibrium
The state of a reversible chemical reaction at which the rates of the forward and reverse reactions are equal and the concentrations of reactants and products remain constant. Equi…
Equilibrium Constant
The equilibrium constant (K) is a dimensionless number that expresses the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised …
Equilibrium Constant
A dimensionless number (K) that expresses the ratio of products to reactants at equilibrium, with each concentration raised to the power of its stoichiometric coefficient. K > 1 fa…
Equilibrium Or Chemical Equilibrium
Chemical equilibrium is the state of a reversible reaction in which the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in the conc…
Equivalence Point
The equivalence point in a titration is the point at which the amount of titrant added is stoichiometrically equal to the amount of analyte in the sample. At the equivalence point,…
Equivalence Point
The point in a titration at which the moles of titrant added are stoichiometrically equal to the moles of the analyte being titrated. At the equivalence point, the reaction between…
Equivalent Weight
Equivalent weight is the mass of a substance (in grams) that reacts with or is equivalent to one mole of hydrogen ions (for acids/bases) or one mole of electrons (for redox reactio…
Equivalents
A unit expressing the reacting capacity of a substance. One equivalent of an acid contains one mole of H⁺ ions; one equivalent of a base contains one mole of OH⁻ ions. Equivalent w…
Erbium
Erbium is a soft, silvery rare earth metal, atomic number 68. Produces characteristic pink/rose colour in glass and gemstones. Er-doped fibre amplifiers (EDFAs) are essential for l…
Essential Oil
Essential oils are concentrated, volatile aromatic compounds extracted from plants by steam distillation, cold pressing, or solvent extraction. They contain complex mixtures of ter…
Ester
An ester is an organic compound formed by the condensation reaction of a carboxylic acid with an alcohol, with the elimination of water. Esters have the general formula RCOOR', whe…
Ester
An organic compound formed by the reaction of a carboxylic acid with an alcohol, releasing water (condensation reaction). Esters have the general formula RCOOR'. They are often fra…
Esterification
The chemical reaction between a carboxylic acid and an alcohol to form an ester and water. It is a reversible, acid-catalyzed reaction (Fischer esterification). The equilibrium is …
Ether
An ether is an organic compound containing an oxygen atom bonded between two carbon groups (R–O–R'). Ethers are relatively unreactive, making them useful as solvents. Diethyl ether…
Ether
An organic compound containing an oxygen atom bonded to two carbon groups (R-O-R'). Ethers are relatively unreactive, good solvents, and have characteristic sweet odors. Diethyl et…
Europium
Europium is a soft, silvery rare earth metal, atomic number 63. The most reactive lanthanide - reacts readily with water and air. Famous for its bright red (Eu3+) and blue (Eu2+) l…
Eutrophication
Eutrophication is the process by which a body of water becomes excessively enriched with nutrients (mainly nitrogen and phosphorus compounds), stimulating the rapid growth of algae…
Evaporation
The conversion of a liquid to vapor at temperatures below the boiling point at the surface of the liquid. It is an endothermic process where higher-energy molecules escape from the…
Evaporation Rate
Evaporation rate is the speed at which a liquid converts to vapor under given conditions of temperature, pressure, humidity, and surface area. It is influenced by the vapor pressur…
Evaporization
Evaporization (also called vaporization) is the phase transition in which a substance changes from its liquid or solid state to the gaseous state. It includes both evaporation (whi…
Excess Reagent
The reactant present in greater amount than required by the stoichiometry of the reaction. After the limiting reagent is fully consumed, the excess reagent remains unreacted. Ident…
Excited State
An excited state is an energy state of an atom or molecule that is higher than its lowest possible (ground) state energy. Electrons can be promoted to excited states by absorbing e…
Excited State
An energy state of an atom, ion, or molecule that is higher than its ground state. Electrons in excited states occupy higher energy orbitals. When electrons return to lower energy …
Exergonic
A process or reaction that releases free energy (negative ΔG). Exergonic reactions are thermodynamically spontaneous and can do work on the surroundings. Cellular respiration is an…
Exothermic
An exothermic process releases heat energy to the surroundings, resulting in a negative enthalpy change (ΔH < 0). Combustion reactions, neutralization of acids and bases, and the f…
Exothermic Reaction
A chemical reaction that releases heat energy to the surroundings, causing the temperature to increase. The enthalpy change (ΔH) is negative. Examples include combustion, neutraliz…
Exothermicity
Exothermicity refers to the property of a reaction or process that releases heat to the surroundings. An exothermic reaction has a negative enthalpy change (ΔH < 0), meaning the pr…
Explosive
An explosive is a reactive substance that can release a large amount of energy in a rapid, exothermic reaction, producing a sudden increase in pressure from rapid gas generation. E…
Explosive Limits
Explosive limits (also called flammable limits) define the range of concentrations of a flammable gas or vapour in air that can ignite and sustain a flame. The Lower Explosive Limi…
Extensive Property
An extensive property is a physical property of a system that depends on the amount (quantity) of matter present. If the system is divided, the extensive property is also divided p…
Extraction
A separation technique that selectively removes a solute from one phase into another based on solubility differences. Liquid-liquid extraction (solvent extraction) uses immiscible …
Extrapolate
To estimate or predict values beyond the range of measured data by extending a known trend, graph, or function. In chemistry, extrapolation is used to find absolute zero from Charl…
About Chemicals Starting With E
This page lists all chemicals in our database beginning with the letter E. Each entry provides the chemical formula, CAS registry number, physical and chemical properties, common uses, and safety information. Use the alphabetical navigation above to browse other letters, or use the search function to find a specific chemical quickly.
Our chemical glossary covers acids, bases, salts, organic compounds, inorganic compounds, solvents, and many more categories. Click on any chemical name to view its full detailed profile.