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CHAPTER 5
Review
General, Organic, & Biological Chemistry
Janice Gorzynski Smith
Concepts to Know
 Define a chemical reaction
 Correctly write a chemical reaction
 Balance reactions by inspection
 Calculate molecular mass for any compound or molecule
 Apply mole ratios within molecules and between molecules.
 Solve stoichiometry problems
 Convert between mass and moles
 Convert between % composition and mass
 Identify limiting reagent
 Calculate percent yield
 Identify reduction and oxidation equations and pick out the
compound being reduced or oxidized
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Smith. General Organic & Biolocial Chemistry 2nd Ed.
Need to Memorize
6.02 x 1023 is Avogadro’s number.
æ Mass due to specific component ö
percent composition = ç
÷ ´100%
è Total molar mass of compound ø
æ actual yield ö
÷÷ ´ 100%
percentage yield = çç
è theoretical yield ø
Oxidation is the loss of electrons from an atom.
Reducing agents are reduced
Reduction is the gain of electrons by an atom.
Oxidizing agents are reduced.
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Smith. General Organic & Biolocial Chemistry 2nd Ed.
Writing and Balancing Equations
aA (physical state) + bB (state)  cC (state) + dD (state)
HOW TO Balance a Chemical Equation
Step [1] Write the equation with the correct formulas.
•The subscripts in a formula can never be changed
to balance an equation, because changing a
subscript changes the identity of a compound.
Step [2]
Balance the equation with coefficients one
element at a time.
Step [3]
Check to make sure that the smallest set
of whole numbers is used.
Smith. General Organic & Biolocial Chemistry 2nd Ed.
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Solve Stoichiometry Problems
aA +
bB
mass A
x÷
MM

mass B
a:b
+
mass C
x÷
MM
moles A
cC
mass D
x÷
MM
moles B
b:c
moles C
dD
x÷
MM
c:d
moles D
a:c
a:d
• Limiting Reactant: Compare moles A & moles B after applying mole ratio.
• The reactant with the least number of moles AFTER mole ratio considered is
the limiting reactant.
• Use limiting reactant # moles to determine moles of products that form
æ actual yield ö
÷÷ ´ 100%
percentage yield = çç
è theoretical yield ø
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Redox Half Reactions
Cu2+ gains 2 e−
Zn2+ + Cu
Zn + Cu2+
Zn loses 2 e–
Each of these processes can be written as an
individual half reaction:
Zn2+ + 2 e−
loss of e−
Oxidation half reaction:
Zn
Reduction half reaction:
Cu2+ + 2e−
gain of e−
Smith. General Organic & Biolocial Chemistry 2nd Ed.
Cu
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