Browse All 960 Chemistry Terms A–Z

Radiometric Dating Nuclear & Radiochemistry years The general technique of determining the age of a sample from the decay of a radioactive nuclide it contains. t = (1/λ) ln(1 + D/P)

Radiopharmaceutical Nuclear & Radiochemistry MBq A radioactive compound administered to a patient for diagnosis or treatment.

Radiotherapy Nuclear & Radiochemistry Gy The medical use of ionising radiation to destroy cancerous tissue.

Raman Spectroscopy Analytical Chemistry & Spectroscopy cm⁻¹ A vibrational technique based on the small shift in frequency of light scattered inelastically by molecules. Δν̃ = ν̃_incident − ν̃_scattered

Random Error Analytical Chemistry & Spectroscopy Various An error that varies unpredictably in size and direction between repeated measurements.

Raoult's Law Solutions & Colligative Properties Pa The partial vapour pressure of each component of an ideal solution equals its mole fraction times its pure vapour pressure. p_A = x_A p°_A

Rate Constant Chemical Kinetics & Catalysis Various The proportionality constant in a rate law, characteristic of a given reaction at a given temperature. k = A e^(−Ea/RT)

Rate Law Chemical Kinetics & Catalysis mol/(L·s) An experimentally determined equation expressing reaction rate as a function of reactant concentrations. rate = k[A]^m[B]^n

Rate-Determining Step Chemical Kinetics & Catalysis Dimensionless The slowest step in a reaction mechanism, which limits the overall rate.

Reactant Stoichiometry & Chemical Reactions mol A starting substance that is consumed during a chemical reaction.

Reaction Intermediate Chemical Kinetics & Catalysis mol/L A species produced in one step of a mechanism and consumed in a later one, so it does not appear in the overall equation.

Reaction Mechanism Chemical Kinetics & Catalysis Dimensionless The detailed sequence of elementary steps by which reactants are converted into products.

Reaction Quotient Chemical Equilibrium Various The same ratio as the equilibrium constant but evaluated with the concentrations actually present at any moment. Q = [C]^c[D]^d / [A]^a[B]^b

Reaction Rate Chemical Kinetics & Catalysis mol/(L·s) The change in concentration of a reactant or product per unit time. rate = −Δ[A]/(aΔt) = Δ[P]/(pΔt)

Reagent Foundations of Chemistry Dimensionless A substance added to a system to bring about a chemical reaction or to test for the presence of another substance.

Real Gas States of Matter & Gas Laws Dimensionless An actual gas whose behaviour deviates from the ideal gas law because its molecules occupy volume and attract one another. Z = pV / nRT ≠ 1

Rearrangement Reaction Stoichiometry & Chemical Reactions Dimensionless A reaction in which the atoms of a molecule are reorganised to give a structural isomer. A → A′ (isomer)

Redox Couple Electrochemistry & Redox V The oxidised and reduced forms of the same species, considered together as a conjugate pair. Ox / Red

Redox Reaction Stoichiometry & Chemical Reactions V A reaction in which electrons are transferred, so that one species is oxidised while another is reduced. Ox₁ + Red₂ → Red₁ + Ox₂

Redox Titration Analytical Chemistry & Spectroscopy mol/L A titration in which the reaction between titrant and analyte involves electron transfer.

Reducing Agent Electrochemistry & Redox V A species that donates electrons to another substance and is itself oxidised in the process.

Reducing Sugar Biochemistry & Polymer Chemistry Dimensionless A sugar with a free aldehyde or ketone group that can reduce mild oxidising agents.

Reduction Electrochemistry & Redox Dimensionless The gain of electrons by a species, accompanied by a decrease in its oxidation number. Xⁿ⁺ + n e⁻ → X

Reference Electrode Electrochemistry & Redox V A half-cell with a stable, known and reproducible potential, used as a fixed point against which other potentials are measured.

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