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Stoichiometry & Chemical Reactions

Elimination Reaction

A reaction in which two substituents are removed from adjacent atoms, generating a multiple bond.

R–CH₂–CHX–R → R–CH=CH–R + HX Dimensionless Inorganic & Coordination Chemistry

Ellingham Diagram

A plot of the standard free energy of formation of metal oxides against temperature, used to choose a reduction route.

ΔG° = ΔH° − TΔS° kJ/mol Foundations of Chemistry

Empirical Formula

The chemical formula giving the simplest whole-number ratio of atoms of each element in a compound.

ratio = (mass % ÷ A_r), normalised Dimensionless Solutions & Colligative Properties

Emulsion

A colloidal dispersion of one liquid as fine droplets throughout another liquid with which it is immiscible.

nm Organic Chemistry

Enantiomer

One of a pair of stereoisomers that are non-superimposable mirror images of each other.

(+) and (−), or R and S degrees Acids, Bases & Salts

End Point

The point in a titration at which the indicator changes colour, signalling that the reaction is judged complete.

mL Thermochemistry & Thermodynamics

Endergonic Reaction

A reaction with a positive Gibbs free energy change, which requires an input of energy to proceed.

ΔG > 0 kJ/mol Stoichiometry & Chemical Reactions

Endothermic Reaction

A reaction that absorbs energy from the surroundings, giving a positive enthalpy change.

ΔH > 0 kJ/mol Chemical Kinetics & Catalysis

Energy Profile Diagram

A plot of potential energy against reaction coordinate showing reactants, transition states, intermediates and products.

kJ/mol Thermochemistry & Thermodynamics

Enthalpy

A thermodynamic state function equal to internal energy plus the product of pressure and volume.

H = U + pV kJ/mol Thermochemistry & Thermodynamics

Enthalpy Level Diagram

A diagram plotting the enthalpies of reactants and products to show the direction and size of the enthalpy change.

kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Atomisation

The enthalpy change when one mole of gaseous atoms is produced from an element in its standard state.

ΔH_at° kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Dilution

The enthalpy change when a solution is diluted from one concentration to another by adding solvent.

ΔH_dil kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Fusion

The enthalpy change when one mole of a solid melts to a liquid at its melting point.

ΔH_fus kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Neutralisation

The enthalpy change when an acid and a base react to form one mole of water under standard conditions.

H⁺ + OH⁻ → H₂O, ΔH = −57.1 kJ kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Reaction

The heat absorbed or released when a reaction occurs at constant pressure in the molar amounts of the balanced equation.

ΔH_rxn = ΣΔH_f(products) − ΣΔH_f(reactants) kJ/mol Solutions & Colligative Properties

Enthalpy of Solution

The heat absorbed or released when one mole of a substance dissolves completely in a large excess of solvent.

ΔH_sol = ΔH_lattice + ΔH_hyd kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Sublimation

The enthalpy change when one mole of a solid converts directly into vapour.

ΔH_sub = ΔH_fus + ΔH_vap kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Vaporisation

The enthalpy change when one mole of a liquid becomes vapour at its boiling point.

ΔH_vap kJ/mol Thermochemistry & Thermodynamics

Entropy

A measure of the dispersal of energy and the number of microscopic arrangements available to a system.

S = k ln W J/(mol·K) Thermochemistry & Thermodynamics

Entropy Change of the Surroundings

The entropy change experienced by the surroundings when they absorb or release heat from a system.

ΔS_surr = −ΔH_sys / T J/K Biochemistry & Polymer Chemistry

Enzyme

A biological catalyst, almost always a protein, that accelerates a specific biochemical reaction.

Dimensionless Chemical Kinetics & Catalysis

Enzyme Catalysis

Catalysis by protein molecules that bind substrates at a specific active site and lower the activation energy dramatically.

Dimensionless Biochemistry & Polymer Chemistry

Enzyme Specificity

The ability of an enzyme to select one substrate, or one class of substrate, and catalyse one particular reaction.

Dimensionless