Chemistry Dictionary Terminology "R"

Chemistry Dictionary

Terminology "R"

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Radiation

High energy particles or rays emitted during the nuclear decay processes.

Radical

An atom or group of atoms that contains one or more unpaired electrons (usually very reactive species)

Radioactive Dating

Method of dating ancient objects by determining the ratio of amounts of mother and daughter nuclides present in an object and relating the ratio to the object?s age via half-life calculations.

Radioactive Tracer

A small amount of radioisotope replacing a nonradioactive isotope of the element in a compound whose path (for example, in the body) or whose decomposition products are to be monitored by detection of radioctivity; also called a radioactive label.

Radioactivity

The spontaneous disintegration of atomic nuclei.

Raoult's Law

The vapor pressure of a solvent in an ideal solution decreases as its mole fraction decreases.

Rate-determining Step

The slowest step in a mechanism; the step that determines the overall rate of reaction.

Rate-law Expression

Equation relating the rate of a reaction to the concentrations of the reactants and the specific rate of the constant.

Rate of Reaction

Change in the concentration of a reactant or product per unit time.

Reactants

Substances consumed in a chemical reaction.

Reaction Quotient

The mass action expression under any set of conditions (not necessarily equlibrium); its magnitude relative to K determines the direction in which the reaction must occur to establish equilibrium.

Reaction Ratio

The relative amounts of reactants and products involved in a reaction; maybe the ratio of moles. millimoles, or masses.

Reaction Stoichiometry

Description of the quantitative relationships among substances as they participate in chemical reactions.

Reducing Agent

The substance that reduces another substance and is oxidized.

Resonance

The concept in which two or more equivalent dot formulas for the same arrangement of atoms (resonance structures) are necessary to describe the bonding in a molecule or ion.

Reverse Osmosis

Forcing solvent molecules to flow through a semipermable membrane from a concentated solution into a dilute solution by the application of greater hydrostatic pressure on concentrated side than the osmotic pressure opposing it.

Reversible Reaction

Reactions that do not go to completion and occur in both the forward and reverse direction.