Half Reaction

A reaction that explicitly shows electrons involved in either oxidation or reduction.

Half-Cell Reactions

Oxidation and reduction reactions at the electrodes.

Half-Life

The time required for the concentration of a reactant to decrease to half of its initial concentration.

Halogens

The nonmetallic elements in Group 7A (F, Cl, Br, I, and At).

Heat

Transfer of energy between two bodies that are at different temperatures.

Heat Capacity

The amount of heat required to raise the temperature of a given quantity of the substance by one degree Celsius.

Heat of Dilution

The heat change associated with the dilution process.

Heat of Hydration

The heat change associated with the hydration process.

Heat of Solution

The heat generated or absorbed when a certain amount of solute is dissolved in a certain amount of solvent.

Heisenberg Uncertainty Principle

It is impossible to know simultaneously both the momentum and the position of a particle with certainty.

Henry’s Law

The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution.

Hess’ Law

When reactants are converted to products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps.

Heterogeneous Equilibrium

An equilibrium state in which the reacting species are not all in the same phase.

Heterogeneous Mixture

The individual components of a mixture remain physically separated and can be seen as separate components.

Heteronuclear

Composed of two or more different elements such as H₂0 or H₂SO₄.

Homogeneous Equilibrium

An equilibrium state in which all reacting species are in the same phase.

Homogeneous Mixture

The composition of the mixture, after sufficient stirring, is the same throughout the solution.

Homonuclear

Composed of only one element such as H₂ or N₂.

Homonuclear Diatomic Molecule

A diatomic molecule containing atoms of the same element.

Homopolymer

A polymer that is made from only one type of monomer.

Hund’s Rule

The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins.

Hybrid Orbitals

Atomic orbitals obtained when two or more nonequivalent orbitals of the same atom combine.

Hybridization

The process of mixing the atomic orbitals in an atom (usually the central atom) to generate a set of new atomic orbitals.

Hydrates

Compounds that have a specific number of water molecules attached to them.

Hydration

A process in which an ion or a molecule is surrounded by water molecules arranged in a specific manner.

Hydrocarbons

Compounds made up only of carbon and hydrogen.

Hydrogen Bond

A special type of dipole-dipole interaction between the hydrogen atom bonded to an atom of a very electronegative element (F, N, O) and another atom of one of the three electronegative elements.

Hydrogenation

The addition of hydrogen, especially to compounds with double and triple carbon-carbon bonds.

Hydronium Ion

The hydrated proton, H₃O⁺.

Hydrophilic

Water-liking.

Hydrophobic

Water-fearing.

Hypothesis

A tentative explanation for a set of observations.