Download balanced - drseemaljelani

Chapter
3
Formulas, Equations,
and Moles
Chemistry, 5th Edition
McMurry/Fay
Atomic and Molecular Mass
•
The atomic masses as tabulated in the periodic table
are the averages of the naturally occurring isotopes.
•
Mass of C = average of 12C and 13C
= 0.9889 x 12 amu + 0.0111 x 13.0034 amu
= 12.011 amu
2
Atomic and Molecular Mass
The mass of a molecule is just the sum of the
masses of the atoms making up the molecule.
m(C2H4O2) = 2·mC + 4·mH + 2·mO
= 2·(12.01) + 4·(1.01) + 2·(16.00)
= 60.06 amu
3
Avogadro and the Mole
•
One mole of a substance is the gram mass value
equal to the amu mass of the substance.
•
One mole of any substance contains 6.02 x 1023
units of that substance.
•
Avogadro’s Number (NA, 6.022 x 1023) is the
numerical value assigned to the unit, 1 mole.
4
Avogadro and the Mole
•
The Mole: Allows us to
make comparisons
between substances
that have
different
masses.
5
Balancing Chemical Equations
•
A balanced chemical equation represents the
conversion of the reactants to products such that
the number of atoms of each element is conserved.
reactants  products
limestone  quicklime + gas
Calcium carbonate  calcium oxide + carbon dioxide
CaCO3(s)  CaO(s) + CO2(g)
6
Balancing Chemical Equations
CaCO3(s)  CaO(s) + CO2(g)
The letters in parentheses following each substance are
called State Symbols
(g) → gas
(l) → liquid (s) → solid (aq) → aqueous
7
Balancing Chemical Equations
A balanced equation MUST have the same number of
atoms of each element on both sides of the equation.
H2 + O2 → H2O
Not Balanced
2H2 + O2 → 2H2O Balanced
8
Balancing Chemical Equations
The numbers multiplying chemical formulas
in a chemical equation are called:
Stoichiometric Coefficients (S.C.)
2H2 + O2 → 2H2O Balanced
Here 2, 1, and 2 are stoichiometric coefficients.
9
Balancing Chemical Equations
Hints for Balancing Chemical Equations:
1)
Save single element molecules for last.
2)
Try not to change the S.C. of a molecule containing
an element that is already balanced.
3)
If possible, begin with the most complex molecule
that has no elements balanced.
10
Balancing Chemical Equations
Hints for Balancing Chemical Equations:
4) Otherwise, trial and error!!
11
Balancing Chemical Equations
CH4 + O2 → CO2 + H2O
Example 1:
Balance O2 last
C is already balanced
Start by changing S.C. of H2O to balance H
CH4 + O2 → CO2 + 2H2O
12
Balancing Chemical Equations
Example 1:
CH4 + O2 → CO2 + 2H2O
Now C and H are balanced
Balance O by changing the S.C. of O2
CH4 + 2O2 → CO2 + 2H2O
BALANCED!
13
Balancing Chemical Equations
Example 2:
B2H6 + O2 → B2O3 + H2O
Balance O last
B is already balanced
Start by changing S.C. of H2O:
B2H6 + O2 → B2O3 + 3H2O
14
Balancing Chemical Equations
Example 2:
B2H6 + O2 → B2O3 + 3H2O
B and H are balanced
Balance O by changing S.C. of O2
B2H6 + 3O2 → B2O3 + 3H2O
BALANCED!
15