Chemical Quantities and Moles
Counting Particles of Matter
• Define the mole as a counting number.
• Relate counting particles to weighing
samples of substances.
• Solve stoichiometric problems using
molar mass.
Counting Particles of Matter
Avogadro’s principle: equal
volumes of gases at the same
temperature and pressure contain
equal numbers of particles
Counting Particles of Matter
stoichiometry
molar mass
mole
molecular mass
Avogadro’s
number
formula mass
A mole always contains the same number
of particles; however, moles of different
substances have different masses.
• Stoichiometry is the study of
quantitative relationships
between reactants and products
in a chemical reaction.
Stoichiometry (cont.)
• The group or unit of measure used
to count number of atoms,
molecules, ions, or formula units is
the mole (abbreviated mol).
• The number of things in a mole is
6.02 × 1023 and is called
Avogadro’s number.
Molar Mass
• Using moles, macroscopic
measurements, such as mass,
can be related to the molecules
involved in a chemical reaction.
• The mass of one mole of a pure
substance is called its molar mass.
Molar Mass (cont.)
• The molar mass of an element is
simply the average atomic mass
of that element stated in grams
rather than atomic mass units.
Molar Mass (cont.)
• The molecular mass of a covalent
compound is the mass in atomic mass
units of one molecule.
– Its molar mass is the mass in grams
of one mole of its molecules.
Molar Mass (cont.)
• The formula mass of an ionic
compound is the mass in atomic
mass units of one formula unit.
– Its molar mass is the mass in
grams of one mole of its formula
units.
Molar Mass and Stoichiometry
• The concept of molar mass makes it
easy to determine the number of
particles in a sample of a substance
by simply measuring the mass of the
sample.
• Use the molar mass to convert
mass to moles or moles to mass.
Using Moles
• Predict quantities of reactants and
products in chemical reactions.
• Determine mole ratios from
formulas for compounds.
• Identify formulas of compounds by
using mass ratios.
Using Moles
mole: group or unit of measure used to
count numbers of atoms, molecules, or
formula units of a substance
Using Moles
molar volume
ideal gas law
theoretical yield
percent yield
empirical formula
Balanced chemical equations
relate moles of reactants to moles
of products.
Using Molar Masses in
Stoichiometric Problems
• Balanced chemical equations and
moles can be used to predict the
masses of reactants or products.
Using Molar Masses in
Stoichiometric Problems (cont.)
Using Molar Volumes in
Stoichiometric Problems
• The molar volume of a gas is the
volume that a mole of gas occupies at a
pressure of one atmosphere (equal to
101 kPa) and a temperature of 0.00°C.
Ideal Gas Law
• The ideal gas law describes the
behavior of an ideal gas in terms of
pressure (P), volume (V),
temperature (T), and number of
moles of gas, n.
PV = nRT (R represents the ideal gas
constant)
Theoretical Yield and Actual Yield
• The amount of product of a chemical
reaction predicted by stoichiometry is
called the theoretical yield.
• The percent yield of a reaction is
the ratio of the actual yield to the
theoretical yield.
Determining Mass Percents
• Percent composition of a
compound can be determined
from its chemical formula.
Composition of
Geraniol
Determining Chemical Formulas
• To determine a chemical formula, find
the relative numbers of each of the
atoms in the formula unit of the
compound.
• The formula of a compound having
the smallest whole-number ratio of
atoms in the compound is called the
empirical formula.
Determining Chemical Formulas (cont.)
Determining Chemical Formulas
• The empirical formula of a
compound can be determined
from its percent composition.
• You can calculate the empirical
formula from percent by mass by
assuming you have 100.00 g of the
compound. Then, convert to mass
of each element to moles.
Section 12.2
Determining Chemical Formulas
• Chemical formulas for most ionic
compounds are the same as their
empirical formulas.
• However, the empirical formula is
not always the chemical formula.
Determining Chemical Formulas
• Many different covalent compounds
have the same empirical formulas
because atoms can share electrons
in different ways.
• The chemical formula of a
compound can be determined if the
molar mass and the empirical formula
are known.
Section 12.2
Key Concepts
• Stoichiometry relates the amounts of products
and reactants in a chemical equation to one
another.
• The mole is a unit used to count particles of
matter. One mole of a pure substance contains
Avogadro’s number of particles, 6.02 x 1023.
• Molar mass can be used to convert mass to
moles or moles to mass.
Key Concepts
• A balanced chemical equation provides mole ratios of the
substances in the reaction.
• The ideal gas law is expressed in the following equation
PV=nRT.
• Percent yield measures the efficiency of a chemical reaction.
• Percent composition can be determined from the chemical
formula of a compound; the empirical formula of a compound
can be determined from its percent composition.
• The chemical formula of a compound can be determined if the
molar mass and the empirical formula are known.