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R
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- R-group
- A symbol used to represent an unspecified side chain in an organic compound.
- racemic mixture
- A mixture of equal amounts of enantiomers.
- rad
- A unit of the energy absorbed by tissue from exposure to radiation; equal to 105 J/g; short for Radiation Absorbed Dose.
- radioactive
- A radioactive element gives off radiation -- alpha particles, beta particles, or gamma rays -- by the disintegration of its nucleus.
- radioactivity
- The release of particles and/or energy from an unstable nucleus.
- radioactivity decay series
- A sequence of spontaneous nuclear reactions ending in the formation of a stable nucleus.
- radiocarbon dating
- The process of measuring the amount of carbon-14 remaining in an organic material and from the measurement calculating the age of the material.
- Rankine
- The temperature scale that uses as its zero point the absolute zero of the temperature scale and that has degrees the same size as the Fahrenheit scale.
- Raoult's law
- The statement that the partial pressure of a solute in equilibrium with a solution is equal to the mole fraction of the solute times the vapor pressure of the pure solute.
- rare earth
- One of the metals appearing either in the third column of the periodic table or among the lanthanides.
- rate constant
- In the differential rate equation, the proportionality constant between the rate and the products of concentrations that determine how the rate varies with concentration.
- rate equation
- An equation that describes the rate of a reaction as a function of the concentrations of reactants (and products), also called rate law.
- rate law
- An equation which describes the rate of a reaction as a function of the concentrations of reactants (and products), also called differential rate equation.
- rate-determining step
- The mechanistic step in a reaction that by its relatively slow rate limits the overall rate of a reaction.
- reactant
- A substance consumed by a chemical reaction.
- reaction mechanism
- The set of elementary steps by which a reaction occurs; the individual steps correspond to molecular collisions.
- redox reaction
- An oxidation-reduction reaction; the term "redox" is obtained from the first few letters of "reduction" and "oxidation."
- reducing agent
- A chemical species that donates electrons in order to reduce another species. In the process the reducing agent is itself oxidized.
- reducing sugar
- A sugar that reacts with copper(II) in a test for available aldehyde groups.
- reduction
- That part of a chemical reaction in which a reactant gains electrons; simultaneous oxidation of a different reactant must occur.
- reference solution
- A reference solution used in spectroscopy is a solution containing all components except the absorbing species of interest. For example, if one wanted to measure the concentration of iodine in the solvent heptane, one would use a reference solution which contained only pure heptane. Iodine is the species which absorbs light and should NOT be present in the reference solution.
- relative humidity
- The ratio of the vapor pressure of water in the air to the equilibrium vapor pressure of water at the same temperature.
- rem
- A unit of radiation that takes into account the biological effectiveness of the radiation; short for Roentgen Equivalent in Man.
- representative element
- One of the elements in the area of the periodic table over which the s and p atomic orbitals are being filled; also called main-group element.
- resonance
- The existence of two or more descriptions of the covalent bonding in an ion or molecule; the bonding is considered to be an average superposition of the individual descriptions.
- ribonucleic acid
- A biological polymer of nucleotides derived that is involved in protein synthesis.
- RNA
- Abbreviation for ribonucleic acid; a biological polymer of nucleotides derived that is involved in protein synthesis.
- roasting
- Heating in the presence of air or oxygen; most commonly used in converting natural metal sulfide ores to oxides as first step in recovery of the metal from its ore.
- rubber
- A tough, elastic polymer obtained from the juices of certain tropical plants; a synthetic material having similar properties.
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