Another way to measure pressure in in millimeters of mercury, which is a measure used in weather and comes from the use of mercury barometers.
Number of Molecules
One last concept that must be mentioned is the number of molecules being observed. This is rather intuitive: the number of molecules is… the number of molecules in the container.
Counting molecules is not easy. They are… small and do not take up much room. Any sample would have a bazillion molecules in it!
bazillion |bəˈzilyən|cardinal number informal, chiefly N. Amer.a very large exaggerated number.
Numbering molecules is usually done by saying how many moles are present.
The mole is the unit of measurement in the International System of Units (SI) for amount of substance. It is defined as the amount of a chemical substance that contains as many elementary entities, e.g., atoms, molecules, ions, electrons, or photons, as there are atoms in 12 grams of carbon-12 (12C), the isotope of carbon with relative atomic mass 12 by definition. This number is expressed by the Avogadro constant, which has a value of 6.022140857(74)×23/mol. The mole is one of the base units of the SI, and has the unit symbol mol.
Avogadro's Number: 6.0221409e+23 = 6.0221409 X 1023