The law stating that the rate of effusion or diffusion of a gas is inversely proportional to the square
root of the gas’s molecular weight.
Gram-equivalent weight
The amount of a compound that contains 1 mole of reacting capacity when fully dissociated. One
GEW equals the molecular weight divided by the reactive capacity per formula unit.
Group
A vertical column of the periodic table, containing elements that are similar in their chemical
properties.
Half-life
The time required for the amount of a reactant to decrease to one-half of its former value.
Half-reaction
Either the reduction half or oxidation half of a redox reaction. Each half-reaction occurs at one
electrode of an electrochemical cell.
Halogens
The active nonmetals in Group VIIA of the periodic table, which have high electronegativities and
highly negative electron affinities.
Heat
The energy representing the kinetic energy of molecules that is transferred spontaneously from a
warmer sample to a cooler sample. See Temperature.
Heat of formation (∆Hf)
The heat absorbed or released during the formation of a pure substance from the elements in their
standard states.