Download I 1 - Teach-n-Learn-Chem

Chemistry
Unit 7:
Chemical Equations
Evidence of a chemical reaction:
odor
heat
sound
light
gas emitted
color change
A reaction has occurred if the chemical and physical
properties of the reactants and products differ.
For a reaction to occur,
particles of reactants
must collide, and with
sufficient energy
collision theory
activation energy: energy needed to start a reaction
Chemical reactions release or absorb energy.
exothermic
reactions
The reaction in an oxyacetylene torch is exothermic.
endothermic
reactions
Photosynthesis is an
endothermic reaction.
catalyst: speeds up reaction wo/being consumed
… it lowers the activation energy (AE)
Energy
without catalyst
AE
with catalyst
AE
time
time
Examples:
enzymes catalyze biochemical reactions
catalytic converters convert CO into CO2
Reaction Conditions and Terminology
Certain symbols give more info about a reaction.
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous
(dissolved in H2O)
NaCl(s)
NaCl(aq)
More on aqueous…
-- “soluble” or “in solution” also indicate that a
substance is dissolved in water (usually)
-- acids are aqueous solutions
Other symbols…
(i.e., clues about the reaction)
means...“yields” or “produces”
heat is added to the reaction
means ______
MgCO3(s)
MgO(s) + CO2(g)
Temp. at which we perform rxn. might be given.
C6H5Cl + NaOH
400oC
C6H5OH + NaCl
The catalyst used might be given.
C2H4(g) + H2(g)
Pt
C2H6(g)
precipitate: a solid product that forms in an
aqueous solution reaction
Na2CO3 (aq) + Ca(NO3)2 (aq)
Na1+
Na1+
CO32–
clear
Na2CO3
solution
Ca2+
CaCO3(s) + 2 NaNO3(aq)
NO31–
NO31–
clear
Ca(NO3)2
solution
ppt
“chunks”
“sinkies”
“floaties”
cloudy solution
containing CaCO3(s)
and NaNO3(aq)
Factors that influence
the rate of a reaction
To make reaction
rate increase…
concentration of reactants
particle size
temperature
mechanical mixing
pressure
catalyst
nature of reactants
use one
N/A
In a reaction:
atoms are rearranged
mass
AND
are conserved
energy
charge
Balancing Chemical Equations
law of
conservation
of mass
=
same # of atoms
of each type on each
side of equation
EX. solid iron reacts with oxygen gas to yield
solid iron (III) oxide
Fe3+ O2–
___Fe(s) + ___O2(g)
___Fe2O3(s)
If all coefficients are 1…
+ ___O
1 2(g)
1
___Fe(s)
1
___Fe
2O3(s)
+
If we change subscripts…
1 3(g)
1
___Fe
2(s) + ___O
+
1
___Fe
2O3(s)
subscript changes the substance.
Changing a ___________
coefficients
To balance, modify only _____________.
superscripts
Right now, _______________
don’t enter into
our “balancing” picture.
4
3 2(g)
+ ___O
___Fe(s)
2
___Fe
2O3(s)
+
Hint: Start with most complicated substances first
and leave simplest substances for last.
solid sodium reacts w/oxygen
to form solid sodium oxide
4
1 2(g)
___Na(s)
+ ___O
Na1+
O2–
2
___Na
2O(s)
+
Aqueous aluminum sulfate reacts w/aqueous calcium
chloride to form a white precipitate of calcium sulfate.
The other compound remains in solution.
Al3+ SO42–
Ca2+ Cl1–
1_ Al2(SO4)3 (aq) + 3_ CaCl2 (aq)
3
_ AlCl3 (aq)
_ CaSO4(s) + 2
Methane gas (CH4) reacts with
oxygen to form carbon dioxide
gas and water vapor.
Furnaces burn
primarily methane.
1
2 O2(g)
_ CH4(g) + _
1
2 H2O(g)
_ CO2(g) + _
1 CaC2(s) + _
1 H2O(l)
_
1
_ C2H2(g) + 1
_ CaO(s)
_
3 CaSi2 + _
2 SbI3
_ Si + 2
_ Sb + 3
_ CaI2
6
_
2 Al + _3
6 CH3OH
_1
2 Al(CH3O)3 + _3 H2
1 C2H2(g) + _
2
5 O2(g)
** _
2 CO2(g) + 1
4
2
_
_ H2O(l)
1 C3H8 + _
5 O2
** _
3 CO2 + _
4 H2O
_
1 C5H12 + _
8 O2
** _
5 CO2 + _
6 H2O
_
** = complete combustion of a hydrocarbon
yields CO2 and H2O
Write equations for the combustion
of C7H16 and C8H18.
1 C7H16 + 11
_
_ O2
7 CO2 + _
8 H2O
_
1
2 C8H18 + 25
_
_ O2
8 CO2 +18
9 H2O
16
_
_
Classifying Reactions
four types
synthesis: simpler substances combine to form
more complex substances
A+B
AB
AB + C
ABC
oxygen + rhombic sulfur
8 O2 + __
1 S8
__
sodium + chlorine gas
2 Na + __
1 Cl2
__
A+B+C
ABC
sulfur dioxide
8 SO2
__
sodium chloride
__
2 NaCl
decomposition: complex substances are broken
down into simpler ones
AB
A+B
ABC
lithium chlorate
Li1+ ClO31–
2
1
_ LiClO3
water
2 H 2O
_
AB + C
ABC
A+B+C
lithium chloride + oxygen
Li1+ Cl1–
2
1_ LiCl + _
3 O2
hydrogen gas + oxygen gas
2
_ H2
1 O2
+ _
single-replacement:
one element
replaces another
AB + C
A + CB
sodium
chlorine +
bromide
Na1+ Br1–
1
_ Cl2 + 2
_ NaBr
copper (II)
aluminum +
sulfate
Cu2+ SO42–
2
_ Al + 3
_ CuSO4
AB + C
B + AC
sodium
+ bromine
chloride
Na1+ Cl1–
2
_ Br2
_ NaCl + 1
aluminum
?
+ copper
sulfate
Al3+ SO42–
1_ Al2(SO4)3 + 3
_ Cu
double-replacement:
AB + CD
iron (III)
+
chloride
Fe3+ Cl1–
1
_ FeCl3 +
AD + CB
potassium
hydroxide
K1+ OH1–
3_ KOH
iron (III) potassium
?
+
hydroxide
chloride
Fe3+ OH1– K1+ Cl1–
1
_ Fe(OH)3 + 3
_ KCl
lead (IV)
calcium
+
nitrate
oxide
lead (IV)
calcium
+
?
oxide
nitrate
Pb4+ NO31– Ca2+ O2–
1
_ Pb(NO3)4 + 2
_ CaO
Pb4+ O2–
Ca2+ NO31–
1_ PbO2 + 2_ Ca(NO3)2
How do we know if a reaction will occur?
For single-replacement reactions, use Activity Series.
In general, elements above replace elements below.
1
1 FeSO4
_ Ba + _
3
_ Mg + 2
_ Cr(ClO3)3
1
_ Fe + 1
_ BaSO4
2_ Cr + _
3 Mg(ClO3)2
_ Pb + _ Al2O3
NR
_ NaBr + 1
_ Cl2
2
_
_ Br2
2 NaCl + 1
_ FeCl3 + _ I2
1_ CoBr2 + 1
_ F2
NR
1 CoF2 + 1
_
_ Br2
For double-replacement reactions,
reaction will occur
water a gas
if any product is:
a precipitate
driving forces
Check new combinations to decide.
1 Pb(NO3)2(aq) + _
2 KI(aq)
1 PbI2(s) + 2
_
_
_ KNO3(aq)
Pb2+ NO31–
K1+ I1–
_ KOH(aq) + _
2
1 H2SO4(aq)
K1+ OH1–
H1+ SO42–
_ FeCl3(aq) + _ Cu(NO3)2(aq)
Fe3+ Cl1–
Cu2+ NO31–
Pb2+ I1– (?)
(ppt)
K1+ NO31– (?)
(aq)
_ K2SO4(aq) + 2
_ H2O(l)
1
K1+ SO42– (?) H1+ OH1– (?)
(aq)
(water)
NR
(aq)
(aq)
Ions in Aqueous Solution
Pb(NO3)2(aq)
Pb(NO3)2(s)
Pb2+(aq) + 2 NO31–(aq)
Pb2+
NO3
1–
NO31–
add
water
NO31–
Pb2+
NO31–
dissociation: “splitting into ions”
NaI(aq)
NaI(s)
Na1+(aq) + I1–(aq)
Na1+
I1–
add
water
Na1+
I1–
Mix them and get the overall ionic equation…
Pb2+
NO31–
reactants
I1–
Na1+
NO31–
Na1+
I1–
1–
1 2+(aq) + __NO
2
2 1+(aq) + __I
2 1–(aq)
__Pb
3 (aq) + __Na
yields
1–(aq) + __Na
1+(aq)
1
2
2
+
__NO
__PbI
(s)
3
2
Na1+
Pb2+
I1–
NO31–
I1–
Na1+
products
NO31–
Cancel spectator ions to get net ionic equation…
2+(aq) + __I
1
2 1–(aq)
__Pb
1
__PbI
2(s)
I1–
Pb2+
I1–
Pb2+
I1–
I1–
Mix together Zn(NO3)2(aq) and Ba(OH)2(aq):
clear Zn(NO3)2 solution
Zn(NO3)2(aq)
Zn2+(aq) + 2 NO31–(aq)
clear Ba(OH)2 solution
Ba(OH)2(aq)
Ba2+(aq) + 2 OH1–(aq)
OH1–
NO31–
Ba2+
Zn2+
NO31–
OH1–
Mix them and get the overall ionic equation…
Zn2+
OH1–
NO31–
Ba2+
NO31–
reactants
OH1–
2+(aq) + __NO
1–
2+(aq) + __OH
1–(aq)
1
2
1
2
__Zn
3 (aq) + __Ba
yields 1
1–(aq) + __Ba
2+(aq)
2
1
__Zn(OH)2(s) + __NO
3
Ba2+
Zn2+
OH1–
products
NO31–
OH1–
NO31–
Cancel spectator ions to get net ionic equation…
1–(aq)
1 2+(aq) + __OH
2
__Zn
1
__Zn(OH)
2(s)
OH1–
Zn2+
Zn2+
OH1–
OH1–
OH1–
Polymers and Monomers
polymer: a large molecule (often a chain) made of
many smaller molecules called monomers
Polymers can be made more rigid if the chains are
linked together by way of a cross-linking agent.
Monomer
Polymer
H H O amino acids………… proteins
H–N–C–C–O–H
nucleotides (w/NR
bases A,G,C,T/U)….. nucleic acids
styrene……………… polystyrene
PVA…………………. “slime”
polyvinyl
alcohol
Quantitative Relationships in Chemical Equations
4 Na(s) +
O2(g)
2 Na2O(s)
Particles
4 atoms
1 m’cule
2 m’cules
Moles
4 mol
1 mol
2 mol
Grams
4g
1g
2g
** Coefficients of a balanced equation represent
# of particles OR # of moles,
but NOT # of grams.
When going from moles of one substance to moles
of another, use coefficients from balanced equation.
mass
vol.
Use coeff. from balanced
equation in crossing this bridge
MOL
mass
vol.
MOL
part.
part.
SUBSTANCE “B”
(unknown)
SUBSTANCE “A”
(known)
4 Na(s) + 1 O (g) 2 Na O(s)
2
2
4 Na(s) + O2(g)
2 Na2O(s)
Na
Na
2O
Na
Na
O22O
How many moles oxygen will react with 16.8 moles sodium?
1 mol O2
16.8 mol Na
= 4.2 mol O2
4 mol Na
How many moles sodium oxide are produced from
87.2 moles sodium?
2 mol Na2O
87.2 mol Na
= 43.6 mol Na2O
4 mol Na
(
(
)
)
How many moles sodium are required
to produce 0.736 moles sodium oxide?
0.736 mol Na2O
(
)
4 mol Na
2 mol Na2O
= 1.472 mol Na
0
0