Browse All 960 Chemistry Terms A–Z

Spectator Ion Stoichiometry & Chemical Reactions Dimensionless An ion present in a reaction mixture that undergoes no chemical change and appears identically on both sides of the equation.

Spectrochemical Series Inorganic & Coordination Chemistry cm⁻¹ A ranking of ligands by the magnitude of the crystal field splitting they produce. I⁻ < Br⁻ < Cl⁻ < F⁻ < H₂O < NH₃ < en < CN⁻ < CO

Spin Quantum Number Atomic Structure & Periodicity Dimensionless The quantum number mₛ describing the intrinsic angular momentum of an electron, restricted to +½ or −½. mₛ = ±½

Spin–Spin Coupling Analytical Chemistry & Spectroscopy Hz The splitting of an NMR signal into multiple lines caused by interaction with neighbouring non-equivalent nuclei. n + 1 rule

Spontaneity Thermochemistry & Thermodynamics kJ/mol The tendency of a process to occur without any continuous external input of energy. ΔG < 0

sp² Hybridisation Chemical Bonding & Molecular Structure degrees The mixing of one s and two p orbitals to give three hybrid orbitals in a plane at 120° to each other. 3 hybrids, 120°

sp³ Hybridisation Chemical Bonding & Molecular Structure degrees The mixing of one s and three p orbitals to give four hybrid orbitals directed towards the corners of a tetrahedron. 4 hybrids, 109.5°

sp³d and sp³d² Hybridisation Chemical Bonding & Molecular Structure degrees Hybridisation schemes involving d orbitals that give five trigonal bipyramidal or six octahedral hybrid orbitals. 5 or 6 hybrids

Square Planar Complex Inorganic & Coordination Chemistry Dimensionless A four-coordinate complex in which the ligands occupy the corners of a square around the metal. dsp² hybridisation

Stability Constant Chemical Equilibrium Various The equilibrium constant for the formation of a complex ion from its metal ion and ligands. K = [MLₙ] / ([M][L]ⁿ)

Stability of Complexes Inorganic & Coordination Chemistry Various The thermodynamic tendency of a complex to persist rather than dissociate into metal ion and free ligands. K_stability

Standard Deviation Analytical Chemistry & Spectroscopy Various A statistical measure of the spread of a set of repeated measurements about their mean. s = √(Σ(xᵢ − x̄)² / (n − 1))

Standard Electrode Potential Electrochemistry & Redox V The potential of a half-cell measured against the standard hydrogen electrode under standard conditions. E° at 298 K, 1 M, 1 bar

Standard Enthalpy of Combustion Thermochemistry & Thermodynamics kJ/mol The enthalpy change when one mole of a substance burns completely in excess oxygen under standard conditions. ΔH_c°

Standard Enthalpy of Formation Thermochemistry & Thermodynamics kJ/mol The enthalpy change when one mole of a compound forms from its elements in their standard states. ΔH_f°

Standard Hydrogen Electrode Electrochemistry & Redox V The reference half-cell, consisting of hydrogen gas at 1 bar bubbled over platinum in 1 M acid, assigned a potential of exactly zero. 2H⁺ + 2e⁻ ⇌ H₂, E° = 0.00 V

Standard Molar Entropy Thermochemistry & Thermodynamics J/(mol·K) The absolute entropy of one mole of a substance in its standard state at 298 K. ΔS° = ΣS°(products) − ΣS°(reactants)

Standard State Thermochemistry & Thermodynamics Dimensionless The reference condition of a pure substance at 1 bar pressure and a stated temperature, conventionally 298.15 K. denoted by °

Standard Temperature and Pressure Foundations of Chemistry K, kPa A defined reference condition used to report and compare gas measurements, currently 0 °C and 100 kPa under IUPAC. T = 273.15 K, p = 100 kPa

Standardisation Analytical Chemistry & Spectroscopy mol/L The determination of the exact concentration of a solution by titrating it against a primary standard. M₁V₁ / n₁ = M₂V₂ / n₂

Starch Biochemistry & Polymer Chemistry Dimensionless The storage polysaccharide of plants, consisting of amylose and amylopectin. (C₆H₁₀O₅)ₙ

State Function Thermochemistry & Thermodynamics Various A property whose value depends only on the current state of the system, not on how that state was reached. ΔX = X_final − X_initial

Static Equilibrium Chemical Equilibrium Dimensionless A state of no change in which the opposing processes have genuinely ceased rather than balancing.

Stationary Phase Analytical Chemistry & Spectroscopy Dimensionless The fixed material in a chromatographic system with which the sample components interact as they pass.

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