Download review CH5 chem121pikul

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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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Need to Memorize
6.02 x 1023 is Avogadro s number.
! Mass due to specific component $
percent composition = #
& '100%
" Total molar mass of compound %
! actual yield $
&& ' 100%
percentage yield = ##
" theoretical yield %
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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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.
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Solve Stoichiometry Problems
aA +
bB
mass A
x÷
MM
mass B
a:b
+
dD
mass C
x÷
MM
moles A
cC
"
mass D
x÷
MM
moles B
b:c
x÷
MM
moles C
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
! actual yield $
&& ' 100%
percentage yield = ##
" theoretical yield %
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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:
Oxidation half reaction:
Zn
Zn2+ + 2 e!
loss of e!
Reduction half reaction:
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Cu2+ + 2e!
gain of e!
Cu
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