Chemistry terms starting with R

Racemic Mixture Organic Chemistry degrees An equimolar mixture of two enantiomers, which shows no net optical rotation. 50:50 (+) and (−)

Radiation Dose Nuclear & Radiochemistry Gy A measure of the energy deposited in matter by ionising radiation. D = E / m

Radioactive Activity Nuclear & Radiochemistry Bq The number of nuclear disintegrations occurring in a sample per unit time. A = λN

Radioactive Decay Series Nuclear & Radiochemistry Dimensionless A sequence of successive radioactive decays leading from a long-lived parent to a stable end product.

Radioactive Half-Life Nuclear & Radiochemistry s The time required for half the nuclei in a radioactive sample to decay. t½ = 0.693 / λ

Radioactive Tracer Nuclear & Radiochemistry Bq A radioisotope introduced into a system so that its pathway can be followed by detecting its radiation.

Radioactive Waste Nuclear & Radiochemistry Bq/kg Material containing radionuclides for which no further use is foreseen and which requires controlled disposal.

Radioactivity Nuclear & Radiochemistry Bq The spontaneous emission of particles or electromagnetic radiation from unstable atomic nuclei.

Radiocarbon Dating Nuclear & Radiochemistry years A dating technique that determines the age of organic material from its residual carbon-14 content. t = (t½ / 0.693) ln(N₀/N)

Radioisotope Nuclear & Radiochemistry Dimensionless An isotope of an element whose nucleus is unstable and undergoes radioactive decay.

Radiolysis Nuclear & Radiochemistry Dimensionless The chemical decomposition of a substance caused by ionising radiation. H₂O →(radiation) H· + OH·

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

Terms starting with R