Glossary of Chemical Terms - H

H

half-cell

An oxidation or reduction reaction that occurs at an electrode.Two half-cells must be combined to form an electrochemical cell.

half-life

The time required for concentration of one substance to reach half of its initial value.The time it takes for one half of a substance to be metabolized and/or excreted from the body.

half-reaction

A reaction that shows the electrons involved in an oxidation or reduction step of a reaction.

halide

A negatively charged ion of the group VIIA elements.

halogen

The group VIIa elements in the periodic table.

heat

The transfer of (thermal) energy between two objects that are at different temperatures.

Henry's Law

The amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

heterocycle

A compound containing at least one ring that consists of both carbon and non-carbon atoms .

heterogeneous

Describes a material or substance or chemical reaction which is not the same throughout in its properties, composition, or state of matter.

homeopathy

A system of disease treatment involving application of minute doses of a remedy that, in a healthy person, would produce symptoms of the disease.

homogeneous

Describes a material or substance or chemical reaction which is the same throughout in its properties, composition, or state of matter.

hybridization

A mixing process, often applied to description of atomic orbitals, producing orbitals that have characteristics intermediate between the various types of orbitals involved.

hydrate

A crystalline solid with molecules of water trapped in the solid state structure, which can often be removed partly or completely by relatively gentle heating.

hydration

Having solvent molecules of water surrounding and becoming attached to ions or molecules of the solute.

hydrocarbon

An organic compound containing only the elements hydrogen and carbon.

hydrolysis

Cleavage of a covalent bond brought about by water; the H- and -OH of water typically become attached to the respective cleavage fragments.For example:

hydrolyze

To add hydrogen or hydroxyl to a substance.

hypothesis

A scientific "hunch," a tentative explanation of or prediction derived from experimentation.

Glossary created by David Shaw (Madison Area Technical College) for The Chemistry Place.

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