unit 7: chemical equations
DESCRIPTION
Honors Chemistry. Unit 7: Chemical Equations. For a reaction to occur, particles of reactants must collide, and with sufficient energy . Evidence of a chemical reaction:. odor . light. heat. gas emitted. sound. color change. A reaction has occurred if the chemical and physical - PowerPoint PPT PresentationTRANSCRIPT
Unit 7: Chemical Equations
HonorsChemistry
Evidence of a chemical reaction:
A reaction has occurred if the chemical and physical
properties of the reactants and products differ.
heatlight
soundgas emittedcolor change
odor
For a reaction to occur,particles of reactantsmust collide, and withsufficient energy
collision theory
activation energy:
Chemical reactions release or absorb energy.
energy needed to start a reaction
exothermic reactions
endothermic reactions
The reaction in an oxy-acetylene torch is exothermic.
Photosynthesis is anendothermic reaction.
catalyst: speeds up reaction wo/being consumed -- it lowers the activation energy (AE)
AEAE
time time
without catalyst with catalyst
Examples: -- enzymes catalyze biochemical reactions -- catalytic converters convert CO into CO2
Ener
gy
Factors that influencethe rate of a reaction
To make reactionrate increase…
concentration of reactants
particle size
temperature
mechanical mixing
catalyst
nature of reactants
use one
N/A
In a reaction:
atoms are rearranged
AND mass
energy
charge
are conserved
Balancing Chemical Equations
=law of
conservationof mass
same # of atomsof each type on each
side of equation
Changing a ________ changes the substance.To balance, modify only __________.
Right now, ___________ don’t enter intoour “balancing” picture.
subscriptcoefficients
superscripts
The thermite reaction(2 Al + Fe2O3 2 Fe + Al2O3)releases enough heat that it
is used for underwater welding.
SiCl4 + H2O SiO2 + HCl
SiClClClCl HHO SiOO HCl
HHO HCl
HCl
HCl
2 4
Rule of Thumb A: Save the simplest substances for last (i.e., choose a complex substance on each side first).
Au2S3 + H2 Au + H2S
AuAuSSS HH Au HHS
HH HHSHHS
HH
Au
33 2
V2O5 + HCl VOCl3 + H2O
VVOOOOO HCl VOClClCl HHO
HCl HHO
HHOHCl
VOClClCl
36
HCl
HCl
HCl
2
Hg(OH)2 + H3PO4 Hg3(PO4)2 + H2O
HgOHOH HHH# HgHgHg## HHO
Rule of Thumb B: If polyatomic ions are the same on both sides of the equation, balance them first.
3 62
HHH#HgOHOH
HgOHOH
HHO
HHO
HHO
HHO
HHO
CaC2(s) + H2O(l) C2H2(g) + CaO(s)
CaSi2 + SbI3 Si + Sb + CaI2
Al + CH3OH Al(CH3O)3 + H2
3 2 26 3
3262 3
2 C2H2(g) + O2(g) CO2(g) + H2O(l) ** 5 4 22
C3H8 + O2 CO2 + H2O ** 5 3 4
C5H12 + O2 CO2 + H2O ** 8 5 6
** = complete combustion of a hydrocarbonyields CO2 and H2O
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…
-- synonyms: “soluble” or “in solution”
-- acids and bases are aqueous solutions
Other symbols…
means...
Temp. at which we perform rxn. might be given.
The catalyst used might be given.
means ______ is added to the reaction
MgCO3(s) MgO(s) + CO2(g)
C2H4(g) + H2(g) C2H6(g) Pt
C6H5Cl + NaOH C6H5OH + NaCl 400oC
“yields” or “produces”
heat
(i.e., clues about the reaction)
precipitate: a solid product that forms in an aqueous solution reaction
When ionic substances have “(aq)” written afterthem, the individual ions have dissociated fromthe ionic crystal and are floating around separately.
Na3PO4(aq) means… 3 Na+(aq) + PO43–(aq)
Sodium phosphate, Na3PO4,(sometimes called “sodium phosphate, tribasic”)
is a cleaning agent and food preservative.
Na2CO3 + Ca(NO3)2 CaCO3 +(aq) (aq)
Na+Ca2+CO3
2–
NO3–
2 (aq)(s)
Na+
NaNO3
NO3–
ppt
clearNa2CO3
solution
clearCa(NO3)2
solution
cloudy solutioncontaining CaCO3(s)
and NaNO3(aq)
“chunks”“sinkies”“floaties”
Word EquationsSolid iron reacts with oxygen gas to yield
solidiron(III) oxide.word equation:
balanced equation:
iron
Fe
+ oxygen iron(III) oxide
O2+ Fe3+ O2–
Fe2O324 3
2
Solid sodium reacts w/oxygento form solid sodium oxide.
O2(g) Na(s) Na2O(s)+
Na+ O2–
+
4
Aqueous aluminum sulfate reacts w/aqueous calciumchloride to form a white precipitate of calcium sulfate.The other compound remains in solution.
Al3+ SO42– Ca2+ Cl–
Al2(SO4)3(s)+ CaCl2 CaSO4 AlCl3(aq) (aq) (aq)+33 2
Write a balanced equation (w/rxn conditions)from the following word equations.
Methane gas (CH4) burns in oxygen.
CH4(g) + O2(g) CO2(g) H2O(g)+2 2
Much of the methane that is liberated duringthe extraction of petroleum is simply burned
because the cost of transporting it is too high.
Write an equation for the combustion of C8H18.
C8H18 + O2 CO2 + H2O 25 8 92 16 18
Classifying Reactions
four types
synthesis: simpler substances combine to form more complex substances
sodium + chlorine gas sodium chloride
A + B AB AB + C ABC A + B + C ABC
Na Cl2+ NaCl2 2
2 2
decomposition: complex substances are broken down into simpler ones
lithium chlorate lithium chloride + oxygen
Li+ ClO3– Li+ Cl–
LiClO3 LiCl + O23
AB A + B ABC AB + C ABC A + B + C
single-replacement: one elementreplaces another
AB + C A + CB AB + C B + AC
? aluminum copper(II)sulfate +
Cu2+ SO42–
CuSO4 Al +Al3+ SO4
2– Al2(SO4)3 Cu+32 3
copper aluminumsulfate +
double-replacement: AD + CBAB + CD
lead(IV)nitrate + calcium
oxide ?
Pb4+ O2– Pb(NO3)4 +
Ca2+ NO3–
CaO Ca(NO3)2 PbO2 +2 2
lead(IV)oxide + calcium
nitrate
How do we know if a reaction will occur?For single-replacement reactions, use Activity Series.In general, elements above replace elements below.
Ba + FeSO4
Mg + Cr(ClO3)3
Pb + Al2O3
NaBr + Cl2
FeCl3 + I2
CoBr2 + F2
Fe + BaSO4
Cr + Mg(ClO3)2
NR
NaCl + Br2
NR
CoF2 + Br2
3 2 2 3
2 2
(?)
For double-replacement reactions,reaction will occurif any product is: water a gas a precipitate
driving forces
Pb(NO3)2(aq) + KI(aq)
KOH(aq) + H2SO4(aq)
FeCl3(aq) + Cu(NO3)2(aq)
H+ OH–
Fe3+ Cl– NO3–
Pb2+ NO3– K+ I– Pb2+ NO3
– K+ I–
Check new combinations to decide.
(?)
K+ SO42–
Cu2+
H+ OH– K+ SO42– (?) (?)
Cl–
Cu2+ (?)
Fe3+ NO 3– (?)
(ppt) (aq)
(aq) (water)
(aq) (aq)
NR
K2SO4(aq) + H2O(l)
PbI2(s) + KNO3(aq) 2 2
2 2
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 4 g 1 g 2 g
** Coefficients of a balancedequation represent # ofparticles OR # of moles,but NOT # of grams.
Part.
Vol.
Mass
MOL
Mass
Vol.
Part.
MOL
SUBSTANCE “A” SUBSTANCE “B”
(known) (unknown)
Use coeff. from bal. eq. to gofrom “moles of A”
to “moles of B”
Na2O 4 Na(s) + O2(g) 2 Na2O(s)
How many moles oxygen will react with 16.8 moles sodium?
How many moles sodium oxide are produced from87.2 moles sodium?
How many moles sodium are requiredto produce 0.736 moles sodium oxide?
( )4 mol Na
1 mol O216.8 mol Na = 4.20 mol O2
87.2 mol Na = 43.6 mol Na2O
( )2 mol Na2O4 mol Na0.736 mol Na2O = 1.47 mol Na
( )2 mol Na2O4 mol Na
O2Na Na2ONa
0 0