Stoichiometry of Formulas and Equations

The mole mol) is the standard unit for amount of substance and consists oiAvogadro s number Q.022x 0 ) of atoms, molecules, or ions. It has the same numerical value in grams as a single entity of the substance has in atomic mass units for example, 1 molecule of H2O weighs 18.02 amu and 1 mol of H2O weighs 18.02 g. Therefore, if the amount of a substance is expressed in moles, we know the number of entities in a given mass of it. 

The subscripts in a chemical formula provide quantitative information about the amounts of each element in a mole of compound. In an empirical formula, the subscripts show the relative number of moles of each element in a molecular formula, they show the actual number. Isomers are different compounds with the same molecular formula. 

In a balanced equation, formulas preceded by integer balancing coefficients are used to show the same numbers of each kind of atom on 

During a typical reaction, one substance (the limiting reactant) is used up, so it limits the amount of product that can form the other reac-tant(s) are in excess. The theoretical yield, the amount based on the balanced equation, is never obtained in the lab because of competing side reactions and physical losses. 

For reactions in solution, we determine amounts of substances from their concentration molarity) and volume. To dilute a solution, we aM solvent, which lowers the amount of solute dissolved in each unit volume. 

Mole-Mass-Number Conversions Mass F ercent 

Molar Ratios from E3alarK d Bjuations Limiting Reactants Reaction Yields 

Solution Mole-Mass-Number Conversions Dilution of Molar Solutions Reactions in Solution 

Concepts Skills to Review Before You Study This Chapter 

The mole (abbreviated mol) is the SI unit for amount of substance. It is defined as the amount of a substance that contains the same number of entities as there are atoms in exactly 12 g of carbon-12. This number is called Avogadro s number, in honor of the 19 -century Italian physicist Amedeo Avogadro, and as you can tell from the definition, it is enormous  

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