1. Intro to Reactions (p. 241 – 250)
Ch. 8 – Chemical Reactions
Intro to Reactions (p. 241 – 250)
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2. Do Now: Answer the following question:
You have 77.3 L of Hydrogen gas at STP, how many moles/atoms of gas do you have?
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3. NOTE CHECK At WEEK’s End
Take all notes and plan to be present on Friday—all in-class practice must be completed and counts as a separate classwork grade!
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4. A.Signs of a Chemical Reaction
Evolution of heat and light
Formation of a gas
Formation of a precipitate
Color change
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5. B.Law of Conservation of Mass
mass is neither created nor destroyed in a chemical reaction
total mass stays the same
atoms can only rearrange
4 H
2 O
4 H
2 O
36 g
4 g
32 g
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6. C. Chemical Equations
A+B  C+D
REACTANTS
PRODUCTS
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7. C. Chemical Equations
p. 246
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8. II. Balancing Equations (p. 250-254)
Ch. 8 – Chemical Reactions
II. Balancing Equations (p )
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9. Coefficient  subscript = # of atoms
A. Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Coefficient  subscript = # of atoms
4. Reduce coefficients to lowest possible ratio, if necessary.
5. Double check atom balance!!!
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10. B. Helpful Tips Balance one element at a time.
Update ALL atom counts after adding a coefficient.
If an element appears more than once per side, balance it last.
Balance polyatomic ions as single units.
“1 SO4” instead of “1 S” and “4 O”
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11. C. Balancing Example 2 Al + CuCl2  Cu + AlCl3 Al Cu Cl 3 3 2 2  1 1
Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2
Al CuCl2  Cu AlCl3 Al Cu Cl 3 3 2
2 
 2
 6
3 
6 
 3
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12. Let’s Practice Ca3(PO4)2 + H2SO4  CaSO4 + H3PO4
Cu + H2SO4  CuSO H2O + SO2
Nickel + hydrochloric acid  Nickel(II) chloride + hydrogen
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13. Your turn: I’ll be working with people who need help at a lab table.
You are responsible for the entirety of the worksheet by the week’s end—note there will be three such sheets over the course of the week!
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14. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
A. Combustion
the burning of any substance in O2 to produce heat
A + O2  B
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
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15. A. Combustion 4 2 Na(s)+ O2(g)  Na2O(s) C3H8(g)+ O2(g)  5 3 4
Products:
contain oxygen
hydrocarbons form CO2 + H2O
Na(s)+ O2(g) 
Na2O(s)
C3H8(g)+ O2(g) 
CO2(g)+ H2O(g)
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16. You try:
__ AlBr3 + __ K  __ KBr + __ Al
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17. B. Synthesis
the combination of 2 or more substances to form a compound
only one product
A + B  AB
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18. B. Synthesis
H2(g) + Cl2(g)  2 HCl(g)
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19. Al(s)+ Cl2(g)  2 3 2 AlCl3(s) B. Synthesis Products:
ionic - cancel charges
covalent - hard to tell
Al(s)+ Cl2(g) 
AlCl3(s)
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20. AB  A + B C. Decomposition
a compound breaks down into 2 or more simpler substances
only one reactant
AB  A + B
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21. C. Decomposition
2 H2O(l)  2 H2(g) + O2(g)
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22. C. Decomposition 2 2 KBr(l)  K(s) + Br2(l) Products:
binary - break into elements
others - hard to tell
KBr(l) 
K(s) + Br2(l)
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23. A + BC  B + AC D. Single Replacement
one element replaces another in a compound
metal replaces metal (+)
nonmetal replaces nonmetal (-)
A + BC  B + AC
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24. Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
D. Single Replacement
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
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25. D. Single Replacement Fe(s)+ CuSO4(aq)  Cu(s)+ FeSO4(aq)
Products:
metal  metal (+)
nonmetal  nonmetal (-)
free element must be more active (check activity series)
Fe(s)+ CuSO4(aq) 
Cu(s)+ FeSO4(aq)
Br2(l)+ NaCl(aq) 
N.R.
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26. AB + CD  AD + CB E. Double Replacement
ions in two compounds “change partners”
cation of one compound combines with anion of the other
AB + CD  AD + CB
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27. Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)
E. Double Replacement
Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)
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28. E. Double Replacement Pb(NO3)2(aq)+ KI(aq)  2 2 PbI2(s)+ KNO3(aq)
Products:
switch negative ions
one product must be insoluble (check solubility table)
Pb(NO3)2(aq)+ KI(aq) 
PbI2(s)+ KNO3(aq)
NaNO3(aq)+ KI(aq) 
N.R.
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