Chemistry Dictionary Terminology "H"

Chemistry Dictionary

Terminology "H"

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Haber Process

A process for the catalyzed industrial production of ammonia from N₂ and H₂ at high temperature and pressure.

Half-Cell

Compartment in which the oxidation or reduction half-reaction occurs in a voltaic cell.

Half-Life

The time required for half of a reactant to be converted into product(s).

The time required for half of a given sample to undergo radioactive decay.

Half-Reaction

Either the oxidation part or the reduction part of a redox reaction.

Halogens

Group VIIA elements: F, Cl, Br, I

Hard Water

Water containing Fe³⁺, Ca²⁺, and Mg²⁺ ions, which forms precipates with soap.

Heat

A form of energy that flows between two samples of matter because of their differences in temperature.

Heat Capacity

The amount of heat required to raise the temperature of a body (of any mass) one degree Celsius.

Heat of Condensation

The amount of heat that must be removed from one gram of a vapor at it's condensation point to condense the vapour with no change in temperature.

Heat of Crystallization

The amount of heat that must be removed from one gram of a liquid at its freezing point to freeze it with no change in temperature.

Heat of Fusion

The amount of heat required to melt one gram of solid at its melting point with no change in temperature. Usually expressed in J/g. The molar heat of fusion is the amount of heat required to melt one mole of a solid at its melting point with no change in temperature and is usually expressed in kJ/mol.

Heat of Solution

The amount of heat absorbed in the formation of solution that contains one mole of solute; the value is positive if heat is absorbed (endothermic) and negative if heat is released (exothermic).

Heat of Vaporization

The amount of heat required to vaporize one gram of a liquid at its boiling point with no change in temperature. Usually expressed in J/g. The molar heat of vaporization is the amount of heat required to vaporize one mole of liquid at its boiling point with no change in temperature and usually expressed ion kJ/mol.

Heavy Water

Water containing deuterium, a heavy isotope of hydrogen.

Heisenberg Uncertainty Principle

It is impossible to determine accurately both the momentum and position of an electron simultaneously.

Henry's Law

The pressure of the gas above a solution is proportional to the concentration of the gas in the solution.

Hess' Law of Heat Summation

The enthalpy change for a reaction is the same whether it occurs in one step or a series of steps.

Heterocyclic Amine

Amine in which the nitrogen is part of a ring.

For further information see Heterocyclic Chemistry

Heterogeneous Catalyst

A catalyst that exists in a different phase (solid, liquid or gas) from the reactants; a contact catalyst.

Heterogeneous Equilibria

Equilibria involving species in more than one phase.

Heterogeneous Mixture

A mixture that does not have uniform composition and properties throughout.

Heteronuclear

Consisting of different elements.

High Spin Complex

Crystal field designation for an outer orbital complex; all t2g and eg orbitals are singly occupied before any pairing occurs.

Homogeneous Catalyst

A catalyst that exists in the same phase (solid, liquid or gas) as the reactants.

For more information see Catalysis

Homogeneous Equilibria

Equilibria involving only one species in a single phase. For example, all gases, all liquids or all solids.

Homogeneous Mixture

A mixture which has uniform composition and properties throughout.

Homologous Series

A series of compounds in which each member differs from the next by a specific number and kind of atoms.

Homonuclear

Consisting of only one element.

Hund's Rule

All orbitals of a given sublevel must be occupied by single electrons before pairing begins (see Aufbau Principle)

Hybridization

Mixing a set of atomic orbitals to form a new set of atomic orbitals with the same total electron capacity and with properties and energies intermediate between those of the original unhybridized orbitals.

Hydrate

A solid compound that contains a definite percentage of bound water.

Hydrate Isomers

Isomers of crystalline complexes that differ in whether water is present inside or outside the coordination sphere

Hydration

Reaction of a substance with water.

Hydration Energy

The energy change accompanying the hydration of a mole of gase and ions.

Hydride

A binary compound of hydrogen.

Hydrocarbons

Compounds that contain only carbon and hydrogen.

Hydrogen Bond

A fairly strong dipole-dipole interaction (but still considerably weaker than the covalent or ionic bonds) between molecules containing hydrogen directly bonded to a small, highly electronegative atom, such as N, O, or F.

Hydrogenation

The reaction in which hydrogen adds across a double or triple bond.

Hydrogen-Oxygen Fuel Cell

Fuel cell in which hydrogen is the fuel (reducing agent) and oxygen is the oxidizing agent.

Hydrolysis

The reaction of a substance with water or its ions.

Hydrolysis Constant

An equilibrium constant for a hydrolysis reaction.

Hydrometer

A device used to measure the densities of liquids and solutions.

Hydrophilic Colloids

Colloidal particles that repel water molecules.

For more information see Colloidal Chemistry