Conversion factor mass-mole-number relationships

Figure 3.8 Summary of the mass-mole-number relationships in a chemical reaction. The amount of one substance in a reaotion is related to that of any other. Quantities are expressed in terms of grams, moles, or number of entities (atoms, molecules, or formula units). Start at any box in the diagram (known) and move to any other box (unknown) by using the information on the arrows as conversion factors. As an example, if you know the mass (in g) of A and want to know the number of molecules of B, the path involves three calculation steps ...

For work in the laboratory, it s necessary to weigh reactants rather than just know numbers of moles. Thus, it s necessary to convert between numbers of moles and numbers of grams by using molar mass as the conversion factor. The molar mass of any substance is the amount in grams numerically equal to the substance s molecular or formula mass. Carrying out chemical calculations using these relationships is called stoichiometry. 

The Per relationship in molar mass, grams per mole, means you can use dimensional analysis to convert from grams to moles or from moles to grams. Molar mass is the conversion factor. This one-step conversion is probably used more often than any other conversion in chemistry because we measure quantities on the macroscopic level in grams. However, chemical reactions take place on the particulate level, and moles are units that express the number of particles. 

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