A mole simply represents Avogadro's number (6.022 x 1023) of molecules. A mole is similar to a term like a dozen. If you have a dozen carrots, you have twelve of them. Similarly, if you have a mole of carrots, you have 6.022 x 1023 carrots. In the equation above there are no numbers in front of the terms, so each coefficient is assumed to be one (1). Thus, you have the same number of moles of AgNO3, NaCl, AgCl, NaNO3.
Converting between moles and grams of a substance is often important. This conversion can be easily done when the atomic and/or molecular mass of the substance(s) are known. Given the atomic or molecular mass of a substance, that mass in grams makes a mole of the substance. For example, calcium has an atomic mass of 40 atomic mass units. So, 40 grams of calcium makes one mole, 80 grams makes two moles, etc.
Molar Mass of Ca = 40.08 (From the Periodic Table)
How many moles of Ca are in 4.50 grams of Ca?
Original Source: Department of Chemistry at UNC Chapel Hill at http://www.shodor.org/unchem/basic/stoic/
|6.0 g CH x||
(24.0 + 2.0)g C H
|= 0.25 mol CH|
|0.25 mol CH x||
2 mol C H
1 mol O
|= 20 g O|