Science / Chemistry Glossary

Flash Point: The temperature when vapor pressure of a substance becomes high enough to allow the air/vapor layer over the substance to be ignited. Ether and acetone have flash points below room temperatu . . . View Full Definition

Fluorescence: A fluorescent substance absorbs short wavelength radiation and re-emits it as radiation with a longer wavelength in a very short time.

Foam: A colloid in which bubbles of gas are suspended in a solid or liquid. Aerogel (solid smoke) and Styrafoam are examples of solid foams; whipped cream is an example of a liquid foam.

Formation: A reaction that forms one mole of a compound from its elements in their most stable forms. For example, the formation reaction for water is H2(g) + ½O2 rightarrow H2O(ell).

Formula Unit: One formula weight of a compound.

Formula Weight: The formula weight is the sum of the atomic weights of the atoms in an empirical formula. Formula weights are usually written in atomic mass units (u).

Fractional Distillation: A technique for separation of liquid mixtures by distillation that uses a tower attached to a flask containing the mixture to perform multiple distillations. Vapor moving up the column conde . . . View Full Definition

Free Energy: Energy that is actually available to do useful work. A decrease in free energy accompanies any spontaneous process. Free energy does not change for systems that are at equilibrium.

Free Radical: A free radical is a molecule with an odd number of electrons. Free radicals do not have a completed octet and often undergo vigorous redox reactions. Free radicals produced within cells can . . . View Full Definition

Freezing Point: The temperature at which the vapor pressure of a liquid is equal to the vapor pressure of the corresponding solid form. The liquid and solid forms can coexist at equilibrium at the freezing . . . View Full Definition

Freezing Point Depression: The freezing point of a solution is always lower than the freezing point of the pure solvent. The freezing point depression is roughly proportional to the molality of solute particles in the . . . View Full Definition

Frequency: The number of cycles of a wave that move past a fixed observation point per second. The SI unit of frequency is the Hertz (Hz).

Fuel Cell: A device that converts the chemical energy obtained from a redox reaction directly into electrical energy.

Functional Group: A substructure that imparts characteristic chemical behaviors to a molecule, for example, a carboxylic acid group.

Gamma Rays: A very high energy form of electromagnetic radiation, typically with wavelengths of less than 3 pm. Gamma rays are produced by certain nuclear decay processes, and are used to sterilize food.

Gas: Matter in a form that has low density, is easily compressible and expandable, and expands spontaneously when placed in a larger container. Molecules in a gas move freely and are relatively f . . . View Full Definition

Gel: A gell is a sol in which the solid particles fuse or entangle to produce a rigid or semirigid mixture. For example, gelatin dissolved in water produces a sol of protein molecules. When the g . . . View Full Definition

Geochemistry: The study of materials and chemical reactions in rocks, minerals, magma, seawater, and soil.

Geometric Isomer: Geometric isomers are molecules that have the same molecular formula and bond connections, but distinctly different shapes.

Gibbs Free Energy: A thermodynamic property devised by Josiah Willard Gibbs in 1876 to predict whether a process will occur spontaneously at constant pressure and temperature. Gibbs free energy G is defined as . . . View Full Definition

Gibbs Free Energy Of Formation: The change in Gibbs free energy that accompanies the formation of one mole of a compound from its elements in their most stable form.

Glutamate: Ionic salts of glutamic acid used as flavor enhancers in many foods. Glutamate is usually manufactured by acid hydrolysis of vegetable proteins. Besides being a basic building block of prote . . . View Full Definition

Glutamate Receptors: Glutamate receptors are protein molecules that helps gate the flow of ions across a nerve cell's membrane. They play a role in the formation of new connections between nerve cells (and so, i . . . View Full Definition

Glutamine: The amide of the amino acid glutamic acid. Glutamic acid often occurs as glutamine when built into proteins.

Glyceride: Glycerides are fats and oils that are esters of glycerol with one or more fatty acids. Monoglycerides, diglycerides, and triglycerides contain one, two, and three fatty acids linked to the g . . . View Full Definition

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