Transcript Chapter 9

Chemical Equations
Ch.9
(9-1) Chemical Rxn
• Substances changed into something
different
• Reactants  Products
– Same type & # of atoms on each side, just
rearranged differently
Evidence of Chemical Change
1.
2.
3.
4.
Heat, light, or sound
Gas
Precipitate (ppt)
Color change
Physical Change
• Same composition before & after rxn
• Ex: melting, boiling
H2O(s)  H2O(l)
Energy
• Chemical rxns absorb or release E
• Exothermic: release E
– Reactants  Products + E
• Endothermic: absorb E
– Reactants + E  Products
Activation E
• Particles must collide for a chemical rxn to
occur & enough E must be present
• Spontaneous rxn: occurs naturally w/out
extra E
• Nonspontaneous: needs more E to start
(9-2) Chemical Equations
• Describes type & # of atoms that are
rearranged during a rxn
• Word eq.:
– Ethanol + oxygen  carbon dioxide + water
• Formula eq.:
– C2H5OH + O2  CO2 + H2O
Coefficients
2 K + Cl2  2 KCl
• 2 K tells how many atoms react
• The 2 applies to everything that follows it
– 2 KCl = 2 K & 2 Cl
• If the coef. is followed by a subscript they
are multiplied
– 2 H 2O = 4 H & 2 O
Subscripts & Superscripts
2 K + Cl2  2 KCl
• Cl2 refers to 2 atoms of Cl
– Diatomics: BrINClHOF
CaCl2  Ca2+ + 2 Cl• Ca2+ tells the charge of an ion
Tips for Balancing Rxns
1. Save H & O for last
2. Treat polyatomic ions as a single
element if on both sides of rxn
•
•
H2SO4 + Al  Al2(SO4)3 + H2
1 sulfate
3 sulfates
3. Balance left to right
Tips for Balancing Rxns
4. Balancing 1 element may unbalance
others
5. If present, make sure charges balance on
each side of eq.
•
HCl + H2O  Cl- + H3O+
Net = 0
Net = 0
•
Ag+ + Cu  Cu2+ + Ag
2Ag+ + Cu  Cu2+ + 2Ag
Net = 2+
Net = 2+
(9-3) States
Symbol
(s)
(l)
(g)
(aq)
Meaning
Solid
Liquid
Gas
In aqueous soln
(dissolved in water)
• C6H12O6(aq) + 6O2(g)  6CO2(g) + 6H2O(l) + E
Conditions
• Conditions:
– Yield: 
– Equilibrium:
– Heat:
heat
..
– Temp./Pressure:
– Catalyst:
Pd
0ºC
1 atm
Equation Info
• Balanced eq. show proportions
• C6H12O6 + 6O2  6CO2 + 6H2O
1 mol
6 mol 6 mol 6 mol
Mole Ratio
• Conversion factor used to convert from 1
type of mole to another
• Compare coef.
C6H12O6 + 6O2  6CO2 + 6H2O
1 mol C6H12O6 : 6 mol CO2
3 mol C6H12O6 x
Mole
Ratio
6 mol CO2 = 18 mol CO2
1 mol C6H12O6
Mole Ratio Practice
Determine the # of moles of each product
would be formed given 16.0 mol KClO3
2 KClO3  2 KCl + 3O2 + 78 kJ
1. List the known
16.0 mol KClO3
Mole Ratio Practice
2. Multiply by the mole ratio (moles that
need to cancel on the bottom)
16.0 mol KClO3 x 2 mol KCl = 16 mol KCl
2 mol KClO3
16.0 mol KClO3 x 3 mol O2 = 24 mol O2
2 mol KClO3
Mole Ratio Practice
3. Now calculate how much E was given off
in kJ
16.0 mol KClO3 x
78 kJ
= 624 kJ
2 mol KClO3
Enthalpy
• ∆H: total E of a system (absorbed or
released)
• Measured in Joules (J)
• Exo: - ∆H
– Stonger bonds produced
• Endo: + ∆H
– E added to break bonds
Exo:
Endo:
(9-4) Types of Reactions
1.
2.
3.
4.
5.
6.
Combustion
Oxidation
Synthesis
Decomposition
Displacement (Single Replacement)
Double Displacement (Double
Replacement)
Combustion
• Violently exo. rxn, usually w/ O2
• Produces CO2 & H2O
• CH4 + 2O2  CO2 + 2H2O + 803 kJ
Oxidation
• Not as dramatic as combustion, but still
involves O2
• Ex: rusting of iron
4Fe + 3O2  2Fe2O3
Synthesis
• Atoms or molecules combine to form a
more complex cmpd
• A + B  AB
• 8 Fe + S8  8 FeS
Polymerization
• Series of synthesis rxns to make a very
large molecule (polymer)
High Density Polyethylene
Decomposition
• Single cmpd is broken down to produce 2
or more simpler substances
• AB  A + B
• 2 H2O  2 H2 + O2
Displacement
• Element replaces another element in a
cmpd
• AB + C  A + BC
• 2Al + 3CuCl2  2AlCl3 + 3Cu
Activity Series
• Order of elements tendency to react w/
H2O & acids
• Displace those below it (less active), but
not above (more active)
• Farther away = quicker rxns
• 2K + MgO  K2O + Mg
more
active
less
active
Displacement Practice
• Mg + CuO  MgO + Cu
– More reactive Mg displaces the less reactive
Cu
• Sn + CaO  SnO + Ca
– No rxn!
– Sn is less reactive than Ca
Double Displacement
• Ions from 2 cmpds interact in soln to form
a product
• AB + CD  AD + CB
• 2KI + Pb(NO3)2  PbI2 + 2KNO3
Rxn Classification Practice
1. NaOH + KNO3  NaNO3 + KOH
– Double displacement
2. 2 C4H10 + O2  8 CO2 + 10 H2O
– Combustion
3. 2 Fe + 6 NaBr  2 FeBr3 + 6 Na
– Single displacement
Rxn Classification Practice
4. CaSO4 + Mg(OH)2  Ca(OH)2 + MgSO4
– Double displacement
5. Pb + O2  PbO2
– Synthesis
6. Na2CO3  Na2O + CO2
– Decomposition
Solubility Rules
• Explain which substances dissolve &
which form precipitates (ppt.)
– Table 13-2, p.492
• Soluble = dissolves (aq)
• Insoluble = ppt (s)
Solubility Practice
NO3-
All nitrates are soluble.
Cl-
All chlorides are soluble except
AgCl, Hg2Cl2, and PbCl2.
• NaNO3 = aq
• KNO3 = aq
• AgCl = s
• ZnCl2 = aq
Ionic Equation
• 2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)
• Total Ionic Eq.:
2K+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq)
 PbI2(s) + 2K+(aq) + 2NO3-(aq)
• Spectator ion: ion that remains unchanged
– K+, NO3-
Net Ionic Equation
• Includes only those cmpds that are
involved in a chemical change
– Omit spectators
• 2I-(aq) + Pb2+(aq)  PbI2(s)