A mole (symbol Mol) is the base unit of quantity of a substance in the metric system. A mole is the quantity of a substance that contains 6. 02 x 1023 units. A “unit” is the smallest measurable entity in the substance, generally either an atom or a molecule. The number of units in a mole was determined by Italian chemist (a scientist specializing in the composition, structure, properties, and reactions of matter) Amedeo Avogadro (1776-1856), one of the founders of modern physical chemistry. For this reason, the value 6. 02 x 1023 is called Avogadro’s number.
One mole of a substance is equal to the substance’s atomic weight (the average weight of an atom of an element) or molecular weight, in grams. You often want to know how many molecules you have in a sample of a substance. Counting the molecules individually would be completely impractical. Even if you had a way to see the individual molecules, there are just too many, even in a tiny sample. Moles were defined to solve the problem of counting large numbers of molecules. With moles, you count the number of molecules in the sample by weighing it.
The mole is useful in chemistry because it allows different substances to be measured comparably. Using the same number of moles of two substances, both amounts have the same number of molecules or atoms. The mole makes it easier to understand chemical equations in practical terms. So the equation: 2H2 + O2 > 2H2O can be understood, as “two moles of hydrogen plus one mole of oxygen yields two moles of water. ” Moles are useful in chemical calculations because they enable the calculation of yields and other values when dealing with particles of different mass.
The Essay on Avogadros Number
... particle, such as atoms, molecules, formula units, electrons or ions, and 1 mole of any substance always contains the same number of molecules. Avogadros number relates the mass ... of a mole of a substance ...
Number of particles is a more useful unit in chemistry than mass or weight, because reactions take place between atoms (for example, two hydrogen atoms and one oxygen atom make one molecule of water) that have very different weights (one oxygen atom weighs almost 16 times as much as a hydrogen atom).
However, the raw numbers of atoms in a reaction are not convenient, because they are very large. Moles can be used in many different ways. Chemical Engineers sometimes measure substance mount in units of gram-moles, kilogram-moles, pound-moles, or ounce-moles; these measure the quantity of a substance whose molecular weight is not equal to its mass in grams, kilograms, pounds, or ounces. Therefore, the mole (unit) takes a major role in the subject chemistry. Not only has the concept of the mole helped to put quantitative information about what happens in a chemical equation on a macroscopic level. The mole can be used to determine the simplest formula of a compound and to calculate the quantities involved in chemical reactions.
