||I U P A C
Organizations & People
of quantities, units and symbols in physical chemistry
1. Base SI units
and physical quantities
A physical quantity is the product
of a numerical value (a pure number) and a unit.
Physical quantities are organized in a dimensional system built upon
seven base quantities. The International System of Units (SI) is based
on the seven base units having the same dimensions as the associated
physical quantities. Their names and symbols are as follows:
|Base Physical Quantity
||Symbol for Quantity
||Name of SI Unit
||Symbol for SI Unit
|amount of substance
The symbol for a physical quantity is a single letter of the Latin
or Greek alphabet printed in italic (sloping) type. It may be modified
by subscripts and/or superscripts of specified meaning, or further characterized
in particular cases through annotations in parenthesies put directly
behind the symbol. The symbol for a unit is printed in roman (upright)
type. Neither symbol should be followed by a full stop (period).
The physical quantity 'amount of substance' or 'chemical amount' is
proportional to the number of elementary entities - specified by a chemical
formula - of which the substance is composed. The proportionality factor
is the reciprocal of the Avogadro constanct L (6.022 x 1023
mol-1). The amount of substance should no longer be called
'number of moles'.
Examples of relations between "amount of substance" and other
2 moles of N2 contain 12.044-x-1023
molecules of N2, amount of N2 = n(N2)
= number of N2 molecules/L;
1.5 moles of Hg2Cl2 have a mass of 708.13 g;
1 mole of photons with frequency 1014 Hz has an energy
of 39.90 kJ;
1 mole of electrons, e-, contains 6.022-x-1023
electrons, has a a mass of 5.468-x-10-7
kg, and a charge of -96.49 kC.
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