Transcript CHM 111 CHAPTER 3-A Moles, Masses, and Chemical Equations © 2012 by W. W.

CHM 111
CHAPTER 3-A
Moles, Masses, and
Chemical Equations
© 2012 by W. W. Norton & Company
The Structure of Atoms
Atomic Mass Unit
1 amu =
1/12 of the mass of on atom of
Carbon-12
1 amu = 1.6605 x 10-24 g
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Atomic and Molecular Mass
mass of carbon12 atom
1 amu 
12
Mass:
proton = 1.00728 amu
neutron = 1.0086 amu
electron = 0.0005486
12C atom = 12.00000 amu
13C atom = 13.00335 amu
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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
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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
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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.
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Avogadro and the Mole
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Avogadro and the Mole
•
Methionine, an amino acid used by organisms to
make proteins, is represented below. Write the
formula for methionine and calculate its molar mass.
(red = O; gray = C; blue = N; yellow = S; ivory = H)
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Avogadro and the Mole
•
The Mole: Allows us to
make comparisons
between substances
that have
different
masses.
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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)
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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
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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
H2 + ½O2 → H2O Balanced
2H2 + O2 → 2H2O Balanced
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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.
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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.
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Balancing Chemical Equations
Hints for Balancing Chemical Equations:
4) Otherwise, trial and error!!
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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
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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!
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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
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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!
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Balancing Chemical Equations
Example 3:
MnO2 + KOH + O2 → K2MnO4 + H2O
Balance O last
Mn is already balanced
Change S.C. of KOH to balance K
MnO2 + 2KOH + O2 → K2MnO4 + H2O
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Balancing Chemical Equations
Example 3:
MnO2 + 2KOH + O2 → K2MnO4 + H2O
Mn, K, and H are balanced (H was balanced by chance)
Balance O
MnO2 + 2KOH + ½O2 → K2MnO4 + H2O
or
2MnO2 + 4KOH + O2 → 2K2MnO4 + 2H2O
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Balancing Chemical Equations
Example 4:
NaNO2 + H2SO4→
NO + HNO3 + H2O + Na2SO4
Hard one (no single element molecules)
S is balanced
Start with NaNO2 to balance Na
2NaNO2 + H2SO4→ NO + HNO3 + H2O + Na2SO4
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Balancing Chemical Equations
Example 4:
2NaNO2 + H2SO4→
NO + HNO3 + H2O + Na2SO4
S, Na, and N are balanced
Cannot balance H without changing S.C. for H2SO4!
Boo! Option 1: trial and error
Option 2: Go on to next problem!
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Balancing Chemical Equations
•
Balance the following equations:
C6H12O6 → C2H6O + CO2
Fe + O2 →
Fe2O3
NH3 + Cl2 →
N2H4 + NH4Cl
KClO3 + C12H22O11 → KCl + CO2 + H2O
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Balancing Chemical Equations
•
Balance the following equations:
C6H12O6 → 2C2H6O + 2CO2
Fe + O2 →
Fe2O3
NH3 + Cl2 →
N2H4 + NH4Cl
KClO3 + C12H22O11 → KCl + CO2 + H2O
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Balancing Chemical Equations
•
Balance the following equations:
C6H12O6 → 2C2H6O + 2CO2
4Fe + 3O2 →
NH3 + Cl2 →
2Fe2O3 (balance O first)
N2H4 + NH4Cl
KClO3 + C12H22O11 → KCl + CO2 + H2O
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Balancing Chemical Equations
•
Balance the following equations:
C6H12O6 → 2C2H6O + 2CO2
4Fe + 3O2 →
NH3 + Cl2 →
2Fe2O3 (balance O first)
N2H4 + NH4Cl
N:H is 1:3 on left, must get 1:3 on right!
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Balancing Chemical Equations
NH3 + Cl2 →
N2H4 + NH4Cl
N:H is 1:3 on left, must get 1:3 on right!
4NH3 + Cl2 →
N2H4 + 2NH4Cl
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Balancing Chemical Equations
•
Balance the following equations:
C6H12O6 → 2C2H6O + 2CO2
4Fe + 3O2 →
4NH3 + Cl2 →
2Fe2O3
N2H4 + 2NH4Cl
KClO3 + C12H22O11 → KCl + CO2 + H2O (tough!)
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Balancing Chemical Equations
•
Balance the following equations:
KClO3 + C12H22O11 → KCl + CO2 + H2O
balance C
KClO3 + C12H22O11 → KCl + 12CO2 + H2O
balance H
KClO3 + C12H22O11 → KCl + 12CO2 + 11H2O
balance O
8KClO3 + C12H22O11 → KCl + 12CO2 + 11H2O
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Balancing Chemical Equations
•
Balance the following equations:
8KClO3 + C12H22O11 → KCl + 12CO2 + 11H2O
balance K (and hope Cl is balanced)
8KClO3 + C12H22O11 → 8KCl + 12CO2 + 11H2O
Balanced!
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Balancing Chemical Equations
•
Write a balanced equation for the reaction of element
A (red spheres) with element B (green spheres) as
represented below:
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