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960 terms · page 39 of 40
Transition State
Chemical Kinetics & Catalysis
kJ/mol
The highest-energy configuration along the reaction coordinate, at which bonds are partly broken and partly formed.
denoted ‡
Transition State Theory
Chemical Kinetics & Catalysis
Various
The theory that treats the activated complex as being in quasi-equilibrium with reactants and calculates rate from its decomposition frequency.
k = (k_BT/h) e^(−ΔG‡/RT)
Transmutation
Nuclear & Radiochemistry
Dimensionless
The conversion of one element into another through a change in the number of protons in the nucleus.
¹⁴N + ⁴He → ¹⁷O + ¹H
Transport Number
Electrochemistry & Redox
Dimensionless
The fraction of the total current carried by a particular ion in an electrolyte solution.
t₊ = λ₊ / (λ₊ + λ₋)
Transuranium Elements
Nuclear & Radiochemistry
Dimensionless
The synthetic elements with atomic numbers greater than 92, beyond uranium in the periodic table.
Z > 92
Triglyceride
Biochemistry & Polymer Chemistry
Dimensionless
An ester formed from glycerol and three fatty acid molecules, the main constituent of fats and oils.
glycerol + 3 RCOOH
Trigonal Bipyramidal Geometry
Chemical Bonding & Molecular Structure
degrees
A shape with five bonded atoms occupying three equatorial and two axial positions around a central atom.
AX₅
Trigonal Planar Geometry
Chemical Bonding & Molecular Structure
degrees
A flat molecular shape with three bonded atoms arranged around a central atom at 120°.
AX₃
Triple Point
States of Matter & Gas Laws
K, Pa
The unique temperature and pressure at which the solid, liquid and vapour phases of a substance coexist in equilibrium.
Trouton's Rule
Thermochemistry & Thermodynamics
J/(mol·K)
The empirical observation that the entropy of vaporisation of many liquids is close to 88 J/(mol·K) at their boiling point.
ΔS_vap = ΔH_vap / T_b ≈ 88
Turnover Number
Chemical Kinetics & Catalysis
s⁻¹
The number of substrate molecules converted per catalytic site per unit time.
TON = molecules converted / active sites
Tyndall Effect
Solutions & Colligative Properties
Dimensionless
The scattering of a light beam by colloidal particles, making the beam's path visible through the medium.
Ultraviolet–Visible Spectroscopy
Analytical Chemistry & Spectroscopy
nm
A technique that measures the absorption of ultraviolet and visible light by electronic transitions within molecules.
A = log(I₀/I)
Unimolecular Reaction
Chemical Kinetics & Catalysis
s⁻¹
An elementary step in which a single molecule rearranges or decomposes.
A → products, rate = k[A]
Unit Cell
States of Matter & Gas Laws
pm
The smallest repeating three-dimensional unit that, when stacked, reproduces the entire crystal lattice.
ρ = ZM / (a³N_A)
Units of the Equilibrium Constant
Chemical Equilibrium
Various
The dimensions carried by an equilibrium constant, determined by the change in the number of moles in the balanced equation.
units = (mol/L)^Δn
Unsaturated Fat
Biochemistry & Polymer Chemistry
Dimensionless
A fat containing one or more carbon–carbon double bonds in its fatty acid chains.
Unsaturated Solution
Solutions & Colligative Properties
mol/L
A solution containing less dissolved solute than it could hold at the given temperature.
Uranium–Lead Dating
Nuclear & Radiochemistry
years
A radiometric method that determines the age of very old rocks from the ratio of uranium to its lead decay products.
²³⁸U → ²⁰⁶Pb (4.47 Ga)
Valence Bond Theory
Chemical Bonding & Molecular Structure
Dimensionless
The bonding model in which a covalent bond forms by the overlap of half-filled atomic orbitals on adjacent atoms.
Valence Bond Theory of Complexes
Inorganic & Coordination Chemistry
Dimensionless
The model describing coordinate bonding as the overlap of filled ligand orbitals with hybridised empty orbitals on the metal.
d²sp³, sp³d², sp³, dsp²
Valence Electron
Atomic Structure & Periodicity
Dimensionless
An electron in the outermost occupied shell of an atom, available for bonding.
Valency
Foundations of Chemistry
Dimensionless
The combining capacity of an element, equal to the number of electrons an atom gains, loses or shares when forming compounds.
Van Arkel Process
Inorganic & Coordination Chemistry
°C
A purification method in which a metal is converted to a volatile iodide and then decomposed on a hot filament.
Ti + 2I₂ ⇌ TiI₄