mass
'no magic to the mole'
amount
molar mass
concentration
solution volume
gas volume
molar gas volume
Avogadro
constant, L
number of
entities, N
Now try the following question.
E5. THE AVOGADRO POSTULATE & MOLAR GAS VOLUME
In 1811 Amadeo Avogadro proposed his now-famous law, which states that equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules.
This law is known variously as Avogadro’s principle, Avogadro’s theory or Avogadro’s hypothesis.
It follows that the amount of a gaseous substance is directly proportional to its volume.
The significance of the law is that it enables changes in the number of molecules taking place during a chemical reaction in the gas phase to be followed by measurement of changes in the total volume or pressure.
The Avogadro principle gives us that equal volumes of gases, e.g.,
All contain equal numbers of atoms under the same conditions of temperature and pressure.
In addition, equal volumes of obviously unrelated gases
all contain equal numbers of molecules under the same conditions of temperature and pressure.
The volume occupied by the atoms or molecules of a gas depend on the temperature and pressure but not its ATOMICITY.
Because gases at low pressure consist, on average, of very widely-spaced molecules, the inter-molecular forces that exist are effectively zero, except during collisions. This forms a basis for the postulates of kinetic-molecular theory (K-MT), describing properties of perfect - ideal - gases by relating p, T & V:
1. no intermolecular forces act except during collisions, ALL of which are perfectly elastic, i.e., energy is conserved;
2. molecules occupy zero volume compared to the volume of their container.
occupy the same effective volume regardless of chemical composition.
As a consequence, the volume occupied by a gas at a given temperature and pressure depends only on the chemical amount present, n, and NOT on its identity – this is a corollary of the Avogadro postulate (1811).
And so the molar volume, Vm, for almost all dilute gases is approximately the same under the same conditions of temperature and pressure.
Random, haphazard motion of
a hypothetical, single particle in a gas due to collisions with other particles - so-called Brownian Motion which is diffusive in nature