Glossary of chemical terms

gal
	Gal is a non-SI unit of acceleration, equal to 1 cm/s2. Also called galileo.
gallon
	Gallon (US) is a unit of volume equal to 3.785412 L. Gallon (UK, Imperial) is a unit of volume equal to 4.546090 L.
gamma radiation
	Gamma radiation is electromagnetic radiation of extremely short wavelength. Gamma radiation ranges in energy from about 10-15 to 10-10 J (10 keV to 10 MeV) (wavelength less than about 1 pm). Gamma rays are emitted by excited atomic nuclei during the process of passing to a lower excitation state. Gamma rays are extremely penetrating and are absorbed by dense materials like lead and uranium. Exposure to gamma radiation may be lethal.
gas
	Gas is a state of matter in which the matter concerned occupies the whole of its container irrespective of its quantity.
gauss
	Gauss (G) is a non-SI unit of magnetic flux density (B). 1 G = 10-4 T.
Gaussian system of units
	Gaussian system of units is a hybrid system used in electromagnetic theory, which combines features of both the electrostatic cgs subsystem (esu) and electromagnetic cgs subsystem (emu). With three base units, it uses em units in magnetism and es units in electrostatics. This involves using the constant c (the velocity of light in vacuum) to interrelate these sets of units.
Gay-Lussac's law
	See Charles' law
gel
	Gels are colloids in which both dispersed and continuous phases have a three-dimensional network throughout the material, so that it forms a jelly-like mass (e.g. gelatine). One component may sometimes be removed to leave a rigid gel (e.g. heating silica gel).
Gibbs free energy
	Gibbs free energy (G) is an important function in chemical thermodynamics, defined by G = H-TS where H is the enthalpy, S the entropy, and T the thermodynamic temperature. Gibbs free energy is the energy liberated or absorbed in a reversible process at constant pressure and constant temperature. Sometimes called Gibbs energy and, in older literature, simply "free energy". Changes in Gibbs free energy, ΔG, are useful in indicating the conditions under which a chemical reaction will occur. If ΔG is negative the reaction will proceed spontaneously to equilibrium. In equilibrium position ΔG = 0.
Gibbs phase rule
	Gibbs phase rule is the relationship used to determine the number of state variables, usually chosen from among temperature, pressure, and species composition in each phase, which must be specified to fix the thermodynamic state of a system in equilibrium: F = C - P + 2 where C is the number of components in a mixture, P is the number of phases, and F is the degrees of freedom, i.e., the number of intensive variables that can be changed independently without affecting the number of phases.
glass transition temperature
	Glass transition temperature is the temperature at which an amorphous polymer is transformed, in a reversible way, from a viscous or rubbery condition to a hard and relatively brittle one.
Glauber's salt
	Glauber's salt is sodium sulfate decahydrate (Na2SO4×10H2O). Loses water of hydration at 100 °C. Energy storage capacity is more than seven times that of water.
glycerides
	Glycerides are esters of glycerol (propane-1,2,3-triol) with fatty acids, widely distributed in nature. They are by long-established custom subdivided into triglycerides, 1,2- or 1,3-diglycerides, and 1- or 2- monoglycerides, according to the number and positions of acyl groups.
grain
	Grain (gr) is a non-SI unit of mass, equal to 64.79891 mg.
Grashof number
	Grashof number (Gr) is a dimensionless quantity used in fluid mechanics, defined by Gr = l3gαΔTρ2/η2 where T is temperature, ρ is density, l is length, η is viscosity, α is cubic expansion coefficient, and g is acceleration of gravity.
gravimetry
	Gravimetry is the quantitative measurement of an analyte by weighing a pure, solid form of the analyte. Since gravimetric analysis is an absolute measurement, it is the principal method for analyzing and preparing primary standards. A typical experimental procedure to determine an unknown concentration of an analyte in solution is as follows: - quantitatively precipitate the analyte from solution - collect the precipitate by filtering and wash it to remove impurities - dry the solid in an oven to remove solvent - weigh the solid on an analytical balance - calculate the analyte concentration in the original solution based on the weight of the precipitate.
gravitational constant
	Gravitational constant (G) is the universal constant in the equation for the gravitational force between two particles F = Gm1m2/r2 where r is the distance between the particles and m1 and m2 are their masses.
gray
	Gray (Gy) is the SI derived unit of absorbed dose of radiation. The gray is the absorbed dose when the energy per unit mass imparted to matter by ionizing radiation is one joule per kilogram (Gy = J/kg). The unit is named after the British scientist Louis Harold Gray (1905-1965).
Grignard reagents
	Grignard reagents are organomagnesium halides, RMgX, having a carbon- magnesium bond (or their equilibrium mixtures in solution with R2Mg + MgX2).

 

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