Unit #8 Chemical Reactions
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Transcript of Unit #8 Chemical Reactions
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Unit #8 Chemical Reactions
Part 2
Predicting Products
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Review
• A chemical reaction is the rearrangement of atoms to form new substance(s). Reactant(s) appear on the left, and product(s) appear on the right.
reactants product
• Example: 2 H2 + O2 2 H2O
• When we look at any chemical reaction, in order for it to be accurate, it must show that the law of conservation of mass is obeyed.
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Law of Conservation of Mass• mass is neither created nor destroyed in a
chemical reaction• total mass stays the same• atoms can only rearrange• So, we need to make sure that there are the
same number of each type of atom on each side of the chemical equation.
• To do this, we add coefficients in front of the compounds until these atoms are “balanced.”
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• Refresh your memory by balancing these equations:
__MgCl2 +__NaOH __Mg(OH)2 +__NaCl
__Fe2(SO4)3 +__KOH __K2SO4 +__Fe(OH)3
22
6 3 2
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Synthesis• 2 or more elements/compounds combine to form 1
product.
• Only one product!
• Analogy: Mixing 2 or more ingredients together to get 1 cake. .
A + B AB
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Al(s)+ Cl2(g) AlCl3(s)2 3 2
Synthesis
Example: 2 Mg + O2 2 MgO
Must crisscross to get new compound!
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• Practice Problems:
• Na + F2
• B + N2
Na + F2 Na F+1 -1
Na + F2 NaF2 2
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• Practice Problems:
• Na + F2
• B + N2
B + N2 B N+3 -3
B + N2 BN2 2
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Decomposition• 1 compound is broken down into 2 or more simpler
elements/compounds.
• only one reactant
• Analogy: A couple breaks up. Or a body decompses.
AB A + B
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KBr K + Br2 2 2
Decomposition
• Example
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• Practice Problems:
• Na2O
Na2O Na O
Na2O Na + O22 4
+2
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Single Replacement
• one element replaces another in a compound– metal replaces metal (+)– nonmetal replaces nonmetal (-)
A + BC B + AC
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Fe(s)+ CuSO4(aq) Cu(s)+ FeSO4(aq)
• Products:
Metal replacement:
2 Na + CuCl2 2 NaCl + Cu
Halogen replacement:
F2 + 2 KCl 2 KF + Cl2– free element must be more active (check activity series)
Br2(l)+ NaCl(aq) N.R.
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Metals Nonmetals
lithium fluorine
potassium chlorine
calcium bromine
sodium iodine
magnesium oxygen
aluminum nitrogen
zinc
chromium
iron
nickel
tin
lead
hydrogen*
copper
mercury
silver
platinum
gold
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Practice
• Can Al replace Li? ____
• Can Cu replace Au? ____
• Can Br replace I? ____
• Can Cl replace F? ____NO
NO
YES
YES
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• Practice Problems: • H2 + PbCl2
• Cl2 + KBr
• Zn + CuS
H2 + PbCl2 No rxn+1 -1+2
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• Practice Problems: • H2 + PbCl2
• Cl2 + KBr
• Zn + CuS
Cl2 + KBr -1 -1+1
K Cl+1 -1
+ Br2
Cl2 + KBr KCl + Br222
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• Practice Problems: • H2 + PbCl2
• Cl2 + KBr
• Zn + CuS
Zn + CuS +2 -2+2
ZnS+2 -2
+ Cu
Zn + CuS ZnS + Cu
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AB + CD AD + CB
Double Replacement• Ions from 2 ionic compounds switch places.
--put the inside ions together and the outside ions together
• --positive ion always goes first in the compound!
• Analogy: 2 couples are dancing, and they switch partners
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Pb(NO3)2(aq)+ KI(aq) PbI2(s)+ KNO3(aq)
Double Replacement
Example:
FeCl2 + Na2CO3 2 NaCl + FeCO3
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Practice #1
• Na2CO3 + Ca(NO3)2
• Na2CO3 + Ca(NO3)2
• Na2CO3 + Ca(NO3)2 NaNO3 +CaCO3
NaNO3 + CaCO3
+1 -1-2 +2
2
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Practice #2
• K3PO4 + MgCl2
• K3PO4 + MgCl2
• K3PO4 + MgCl2 KCl + Mg3(PO4)2
KCl + Mg3(PO4)2
+1 -1-3 +2
2 3 6
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Combustion
CH4(g) + 2O2(g) CO2(g) + 2H2O(g)
• Also known as burning; always follows the same form:• The compound always burns in oxygen gas and always
releases carbon dioxide and water.• During incomplete combustion (a limited amt. of O2),
carbon monoxide (CO) is also produced.
C & H (& sometimes O) + O2 CO2 + H2O
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• Example:
• 2 C3H6 + 9 O2 6 CO2 + 6 H2O*always balance in order: C, H, O
• Practice Problems:
CH4 + O2
C6H14 + O2
CO2 + H2O22
CO2 + H2O12 142 19