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A substance that speeds up a chemical reaction without being consumed itself in the reaction.
A substance that alters (usually increases) the rate at which a reaction occurs.

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Inert s-pair Effect

Characteristic of the post-transition minerals, tendency of the outermost s electrons to remain nonionized or un shared in compounds.

Alkylbenzene

A compound containing an alkyl group bonded to a benzene ring.

Mass Number

The sum of the numbers of protons and neutrons in an atom, an integer.

Salinometer

An instrument for measuring the amount of salt in a solution. Also,"salimeter, salometer."

Moderator

A substance such as hydrogen, deuterium, oxygen or paraffin capable of slowing fast nuetrons upon collision.

Polymerization

The combination of many small molecules to form large molecules.

Absolute Entropy (of a substance)

The increase in the entropy of a substance as it goes from a perfectly ordered crystalline form at 0 °K (where its entropy is zero) to the temperature in question.

Entropy is a measure of the “dilution” of thermal energy.

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.

Formula Weight

The mass of one formula unit of a substance in atomic mass units.

 

Effective Nuclear Charge

The nuclear charge experienced by the outermost electrons of an atom, the actual nuclear charge minus the effects of shielding due to inner-shell electrons.
Example: Set of dx2-y2 and dz2 orbitals, those d orbitals within a set with lobes directed along the x-, y-, and z-axes.