H

half-life half-reaction
halogen hard water
hcp heat
heat capacity heat of formation
heat of fusion heat of reaction
heat of vaporization Henry's law
Hess' law heterocyclic
heterogeneous mixture hexagonal closest packed
homogeneous mixture homologous series
Hund's rule hybrid orbital
hybridization hydrate
hydration energy hydrocarbon
hydrogen bond hydrogenation
hydrolysis hydrolyze
hydrophilic hydrophobic
hydroxyl group hygroscopic




half-life

In chemical kinetics, the time it takes for one half of the limiting reactant to be consumed. In nuclear chemistry, the time for half of a sample to undergo radioactive decay.


half-reaction

A portion of an oxidation-reduction reaction involving only the oxidation or only the reduction portion; useful in balancing oxidation-reduction reactions and assigning electrode potentials.


halogen

One of the elements in the same column of the periodic table as fluorine.


hard water

Water containing high concentrations of cations having charge greater than +1; hardness can be removed by ion exchange.


hcp

Abbreviation for hexagonal closest packed; one of two schemes for closest packing of spheres; described as "aba" to indicate that the atoms of the third layer lie directly above the atoms of the first layer.


heat

Energy transferred as a result of a temperature difference; a form of energy stored in the movement of atomic-sized particles.


heat capacity

The quantity of heat needed to raise the temperature of a sample of matter by one unit.


heat of formation

The heat absorbed during the formation of one mole of a compound from its component elements in their most stable forms.


heat of fusion

The heat absorbed as a substance melts.


heat of reaction

The heat absorbed as a reaction occurs.


heat of vaporization

The heat absorbed as a substance passes from a liquid to a gas.


Henry's law

The statement that the partial pressure of a gas in equilibrium with a solution is proportional to the concentration of the dissolved gas in the solution.


Hess' law

The scheme for adding thermodynamic parameters for a reaction when the reactions are added.


heterocyclic

A cyclic organic compound containing rings formed by carbon and other atoms.


heterogeneous mixture

A mixture in which regions differ in composition or state of matter.


hexagonal closest packed

One of two schemes for closest packing of spheres; described as "aba" to indicate that the atoms of the third layer lie directly above the atoms of the first layer.


homogeneous mixture

A mixture in which all regions have the same composition.


homologous series

A sequence of compounds having the same functional groups but differing in the length of the chain of carbon atoms.


Hund's rule

The statement that electrons singly occupy all degenerate orbitals before doubling up in an orbital.


hybrid orbital

An orbital formed by mathematically combining atomic orbitals to generate an equivalent set of orbitals more consistent with the observed bonding geometry.


hybridization

The process of mathematically combining atomic orbitals to generate an equivalent set of orbitals more consistent with the observed bonding geometry; a description (sp, etc.) of what orbitals were combined.


hydrate

A substance that solidifies so as to include water of crystallization.


hydration energy

The energy absorbed as a substance is dissolved in water.


hydrocarbon

A compound containing only the elements carbon and hydrogen.


hydrogen bond

An attractive force, either intramolecular or intermolecular, between an electronegative atom and a hydrogen atom attached to another electronegative atom.


hydrogenation

Any reaction of hydrogen with an organic compound.


hydrolysis

The reaction of an anion with water to form the conjugate acid and hydroxide ion; a reaction in which water reacts with a substance to break it into components.


hydrolyze

To react with water so that the water molecule is split into two parts, H and OH.


hydrophilic

Water-loving; attracted to water molecules and polar molecules.


hydrophobic

Water-hating; not attracted to water molecules or polar molecules.


hydroxyl group

The functional group of an oxygen atom bonded to an hydrogen atom, -OH; found in alcohols.


hygroscopic

Absorbing moisture from the air.



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