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H
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- 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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