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960 terms · page 34 of 40
Sandwich Compound
Inorganic & Coordination Chemistry
Dimensionless
An organometallic compound in which a metal atom is held between two parallel planar cyclic ligands.
e.g. Fe(C₅H₅)₂
Saponification
Stoichiometry & Chemical Reactions
Dimensionless
The alkaline hydrolysis of an ester, particularly a triglyceride, to give a carboxylate salt and an alcohol.
RCOOR′ + NaOH → RCOONa + R′OH
Saturated Fat
Biochemistry & Polymer Chemistry
Dimensionless
A fat whose fatty acid chains contain only single carbon–carbon bonds.
Saturated Solution
Solutions & Colligative Properties
mol/L
A solution in dynamic equilibrium with undissolved solute, containing the maximum amount that will dissolve at that temperature.
rate dissolve = rate crystallise
Saturation and Unsaturation
Organic Chemistry
Dimensionless
The distinction between compounds containing only single bonds and those containing multiple bonds or rings.
DoU = (2C + 2 + N − H − X)/2
Schottky Defect
States of Matter & Gas Laws
Dimensionless
A point defect in which equal numbers of cations and anions are missing from their lattice sites.
Schrödinger Wave Equation
Atomic Structure & Periodicity
J
The fundamental equation of quantum mechanics whose solutions give the allowed energies and wavefunctions of a system.
Ĥψ = Eψ
Scintillation Counter
Nuclear & Radiochemistry
counts/s
A detector in which radiation causes a material to emit flashes of light that are counted and measured.
Second Law of Thermodynamics
Thermochemistry & Thermodynamics
J/K
The total entropy of the universe increases in every spontaneous process.
ΔS_universe > 0
Second-Order Reaction
Chemical Kinetics & Catalysis
L/(mol·s)
A reaction whose rate depends on the square of one concentration or on the product of two concentrations.
1/[A] = 1/[A]₀ + kt
Secondary Cell
Electrochemistry & Redox
V
A cell whose reaction can be reversed by an applied current, allowing it to be recharged and reused.
Secondary Standard
Analytical Chemistry & Spectroscopy
mol/L
A solution whose concentration has been established by titration against a primary standard.
Secondary Structure
Biochemistry & Polymer Chemistry
Dimensionless
Local regular folding patterns of a polypeptide backbone stabilised by hydrogen bonds.
Secondary Valence
Inorganic & Coordination Chemistry
Dimensionless
In Werner's theory, the non-ionisable valence corresponding to the coordination number, satisfied by ligands in fixed spatial positions.
Secular Equilibrium
Nuclear & Radiochemistry
Bq
The steady state reached when a long-lived parent supports a short-lived daughter at constant activity.
λ₁N₁ = λ₂N₂
Selective Discharge
Electrochemistry & Redox
V
The preferential reaction of one ion over others at an electrode during electrolysis.
Selective Precipitation
Chemical Equilibrium
mol/L
The separation of ions from a mixture by adding a reagent that precipitates them one at a time.
Selectivity
Chemical Kinetics & Catalysis
Dimensionless
The ability of a catalyst to direct a reaction towards one particular product among several possible ones.
selectivity = desired product / total product
Self-Ionisation of Water
Acids, Bases & Salts
mol/L
The reaction in which two water molecules transfer a proton to give a hydronium and a hydroxide ion.
2H₂O ⇌ H₃O⁺ + OH⁻
Semipermeable Membrane
Solutions & Colligative Properties
Dimensionless
A barrier that allows solvent molecules to pass while blocking larger solute particles.
Sensitivity
Analytical Chemistry & Spectroscopy
Various
The change in an instrument's response for a given change in analyte concentration.
S = dSignal / dConcentration
Shielding Effect
Atomic Structure & Periodicity
Dimensionless
The reduction in the nuclear attraction felt by an outer electron caused by repulsion from electrons in inner shells.
Z_eff = Z − σ
SI Base Units
Foundations of Chemistry
Various
The seven defined units of the International System from which every other measurement unit is derived.
Sievert
Nuclear & Radiochemistry
Sv
The SI unit of equivalent dose, weighting absorbed dose by the biological damage the radiation type causes.
H = D × w_R