Chemistry terms starting with R

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.

Relationship between K and Rate Constants Chemical Equilibrium Various The equilibrium constant of an elementary reaction equals the ratio of its forward and reverse rate constants. K = k_forward / k_reverse

Relationship between Ka and Kb Acids, Bases & Salts Dimensionless The reciprocal link between the strengths of an acid and its conjugate base. Ka × Kb = Kw

Relationship between Kp and Kc Chemical Equilibrium Dimensionless The conversion linking the pressure and concentration forms of the equilibrium constant for a gaseous reaction. Kp = Kc(RT)^Δn

Relative Atomic Mass Foundations of Chemistry Dimensionless The weighted average mass of the atoms of an element, expressed relative to one twelfth the mass of a carbon-12 atom. A_r = Σ(isotope abundance × isotope mass)

Relative Lowering of Vapour Pressure Solutions & Colligative Properties Dimensionless The fractional reduction in a solvent's vapour pressure caused by dissolving a non-volatile solute. (p° − p) / p° = x_solute

Resonance Chemical Bonding & Molecular Structure Dimensionless The description of a molecule whose true structure is a weighted average of two or more valid Lewis structures. A ↔ B ↔ C

Resonance Effect Organic Chemistry Dimensionless The delocalisation of pi or lone pair electrons through a conjugated system, altering electron density at distant atoms. −M and +M effects

Resonance Energy Chemical Bonding & Molecular Structure kJ/mol The extra stability a molecule gains from electron delocalisation, measured against the most stable single Lewis structure. ΔE_res = E(hybrid) − E(best structure)

Retention Factor Analytical Chemistry & Spectroscopy Dimensionless The ratio of the distance travelled by a component to the distance travelled by the solvent front. Rf = d_spot / d_solvent

Reverse Osmosis Solutions & Colligative Properties atm The forced flow of solvent from a concentrated to a dilute solution by applying pressure greater than the osmotic pressure. p_applied > π

Reversible Process Thermochemistry & Thermodynamics J An idealised process carried out through a continuous series of equilibrium states, so it can be reversed by an infinitesimal change. w_rev = −∫p dV

Reversible Reaction Stoichiometry & Chemical Reactions Dimensionless A reaction that can proceed in both the forward and reverse directions under the same conditions. A + B ⇌ C + D

RNA Biochemistry & Polymer Chemistry Dimensionless A generally single-stranded nucleic acid that carries out the expression of genetic information.

Terms starting with R