UNIT VI - CHEMICAL EQUATIONS
1
I. Introduction
A. chemical reaction - any chemical change
B. chemical equation - set of symbols and numbers which represent a chemical change
1. reactants - what you begin with
2. products - what you end up with
Reactants Products
C. Conservation of Mass - mass of reactants = mass of products
II. Naming Reactants and Products
A. Compounds
1. Ionic, Molecular, Acids – we did this Unit V
2. Other Good Names to know
methane (CH4) propane (C3H8)
butane (C4H10)
ammonia (NH3) water (H2O)
octane (C8H18)
B. Elements
1. monatomic elements - elements composed of a series of single atoms
* examples: iron (Fe), sodium (Na), silicon (Si), carbon (C)
2. diatomic elements - elements composed of a series of molecules composed of two atoms
of that element; “magic seven”
* examples: nitrogen (N2), oxygen (O2), chlorine (Cl2)
S. Give the formulas for the following elements and compounds:
K
1) potassium
CO2
2) carbon dioxide
FeS
3) iron(II) sulfide
Fe
4) iron
HBr
5) hydrobromic acid
Br2
6) bromine
AgNO3
7) silver nitrate
W3(PO4)5 10)
tungsten (V)
phosphate
Ag2CrO4
H2SO4
8) silver chromate
11) sulfuric acid
CuSO4
AlI3
9) copper(II)
sulfate
12) aluminum
iodide
UNIT VI - CHEMICAL EQUATIONS
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III. Balancing Equations
Word Equation: Methane combusts with oxygen to form carbon dioxide and water
Formula Equation: CH4 + O2 CO2 + H2O
reactants: CH4 & O2
Draw a picture:
product(s): CO2 & H2O
O
H
O
O
O
H
C
+
C
H
H
H
O
O
O
O
H
CH4
+
2 O2
CO2
H
+
+
H
2 H2O
Does this follow conservation of mass?
- correct errors like shown above by using coefficients to indicate the number of molecules of each
participant
- once the correct formula for a compound is determined, DO NOT CHANGE THE SUBSCRIPTS TO
BALANCE THE EQUATION!!!!
- Suggested order of balancing:
1)
2)
3)
4)
5)
Balance polyatomic ions, ONLY if it appears on both the reactant and product sides.
Balance metals.
Balance nonmetals, except hydrogen and oxygen
Balance hydrogen and oxygen.
Double check your balancing and adjust as necessary.
Balance the following equations, then list the reactant(s) and product(s):
T.
1)
2 Mg + 1 O2 2 MgO
2)
1 Zn + 2 CuNO3 1 Zn(NO3)2 + 2 Cu
3)
1 Na2CO3 1 Na2O + 1 CO2
4)
2 Al(NO3)3 + 3 K2CO3 1 Al2(CO3)3 + 6 KNO3
5)
1 C5H12 + 8 O2 5 CO2 + 6 H2O
UNIT VI - CHEMICAL EQUATIONS
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S.
1)
1
CH4 +
2)
4
Na +
1
O2 3)
3
Na +
1
Mo(OH)3 4)
1
C7H16 +
2
1
O2 11
2
O2 2
CO2 +
H 2O
Na2O
3
7
NaOH +
1
8
H 2O
CO2 +
Mo
5) iron + oxygen iron(III) oxide
4 Fe + 3 O2 2 Fe2O3
6) aluminum sulfate + calcium chloride aluminum chloride + calcium sulfate
1 Al2(SO4)3 + 3 CaCl2 2 AlCl3 + 3 CaSO4
T. What are the reactants and products for the 6 student practice equations?
Problem Reactants
1
CH4 , O2
Products
CO2 , H2O
2
Na , O2
Na2O
3
Na , Mo(OH)3
NaOH , Mo
4
C7H16 , O2
CO2 , H2O
5
Fe , O2
Fe2O3
6
Al2(SO4)3 , CaCl2
AlCl3 , CaSO4
UNIT VI - CHEMICAL EQUATIONS
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IV. 5 types of reactions
* many chemical reactions follow a specific pattern - makes products predictable
A. Synthesis - general form: A + B AB
* we will mostly deal with synthesis of two elements into one compound
* Note one is a metal and one is a nonmetal, so we will charge-balance our products:
T.
1) ______ Mg + _______ O2 put together reactants: Mg+2 and O-2
charge balance product: MgO
balance equation:
2 Mg + O2 MgO
2) ______ Na + ________ Cl2 Na+ and Cl- NaCl
2 Na + Cl2 2 NaCl
3) ______ H2O + _______ CO2 special synthesis (water + nonmetal oxide acid)
* simply put everything together in one compound beginning w/ H:
H2O + CO2 H2CO3
S.
1) _______ K + _______ O2 K+ and O-2 K2O
4 K + O2 2 K2O
2) _______ Al + _______ O2 Al+3 and O-2 Al2O3
4 Al + 3 O2 2 Al2O3
3) _______ H2O + _______ SO3 H2SO4
B. Decomposition - general form: AB A + B
* usually requires an input of energy
T.
1) ______ HgO balance the equation:
break up the compound into its elements
if element is diatomic, mark it appropriately: Hg + O2
2HgO 2 Hg + O2
2) ______ H2O 2 H2O 2 H2 + O2
S.
1) ______ Ag2O 2 Ag2O 4 Ag + O2
2) ______ NaCl 2 NaCl 2 Na + Cl2
UNIT VI - CHEMICAL EQUATIONS
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C. Single Replacement - general form: element + ionic compound ionic compound + element
* element replaces element similar to it, i.e. metal replaces metal, nonmetal replaces nonmetal
* only occurs if free element is more active than its counterpart
Activity Series
most active
least active
METALS: Li, Rb, K, Cs, Ba, Sr, Ca, Na, Mg, Al, Mn, Zn, Cr, Fe, Cd, Co, Ni, Sn, Pb, H2, Bi, Cu, Hg, Ag, Pt, Au
T.
1) _____ Li + _____ CuSO4 Li wants to trade w/ Cu, it will because it is more
active (see above)
switch metals to form products: LiSO4 + Cu
charge balance new compound: Li2SO4
mark new element if diatomic: Cu
balance equation:
2 Li + CuSO4 Li2SO4 + Cu
2) _____ Fe + _____ NaNO3 Fe is NOT more active than Na NR
3) _____ Zn + _____ HCl Zn is more active than H
new products: ZnCl2 + H2
Zn + 2 HCl ZnCl2 + H2
4) _____ Ni(NO3)2 + _____ Al Al is more active than Ni
new products: Al(NO3)3 + Ni
3 Ni(NO3)2 + 2 Al 2 Al(NO3)3 + 3 Ni
S.
1)
3 Na + 1 FeCl3 3 NaCl + Fe
2)
2 Al + 3 ZnSO4 Al2(SO4)3 + 3 Zn
3)
Co + K2CO3 NR
4)
2 K + CaI2 2 KI + Ca
5)
Mg + Co(NO3)2 Mg(NO3)2 + Co
6)
CaCl2 + Cu NR
7)
Al(NO3)3 + 3 Na 3 NaNO3 + Al
UNIT VI - CHEMICAL EQUATIONS
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V. Representing Phases in Equations
solid - (s)
liquid - (l)
gas - (g)
aqueous solution - (aq)
S. Show proper phase notation with formulas for the following:
Cl2(g)
1) chlorine gas
4) ice
H2O(s)
2) water
H2O(l)
5) sodium chloride
crystals
NaCl(s)
3) steam
H2O(g)
6) sodium chloride NaCl(aq)
dissolved in water
IV (con’t).......
D. Double Replacement - general form: AX(aq) + BY(aq) AY + BX
* the ions “switch partners”
* only occurs if one of the products is a solid precipitate
* precipitate – an ionic compound formed by a double-replacement reaction
which is not soluble in water
* it forms a cloudy appearance in the solution; if allowed to sit, the precipitate
will settle to the bottom of the container
Solubility Rules for Ionic Compounds
Always Soluble (aqueous)
Name
Symbol
Group I Metals
Ammonium
Acetate
Nitrate
Li+1 Na+1 K+1
NH4+1
C2H3O2-1
NO3-1
Generally Insoluble (form precipitates)
Name
Symbol
Exceptions
carbonate
chromate
phosphate
sulfide
hydroxide
CO3-2
CrO4-2
PO4-3
S-2
OH-1
Group I Metals, ammonium
Group I Metals, ammonium
Group I Metals, ammonium
Group I & II Metals, ammonium
Group I Metals, Ca+2, Sr+2, Ba+2, ammonium
Mostly Soluble (usually aqueous)
Name
Symbol
Precipitates with (solid)
halide ions (X)
sulfate
Cl-1, Br-1, I-1
SO4-2
AgX, HgX2, PbX2
SrSO4, BaSO4, PbSO4, Hg2SO4
UNIT VI - CHEMICAL EQUATIONS
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T.
1) _____ NaOH(aq) + _____ AgNO3(aq) switch metal ions: NaNO3 + AgOH
check solubility: NaNO3 is soluble, so mark it as NaNO3(aq)
AgOH is insoluble, so this is your precipitate: AgOH(s)
because you formed a precipitate, there is a reaction, so charge-balance products: NaNO3(aq) + AgOH(s)
balance the equation:
NaOH(aq) + AgNO3(aq) NaNO3(aq) + AgOH(s)
2) _____ NiSO4(aq) + _____ Li3PO4(aq) switch ions: NiPO4 + LiSO4
charge balance products:
NiPO4 is insoluble, and LiSO4 is soluble:
Ni3(PO4)2(s) + Li2SO4(aq)
NiPO4(s) + LiSO4(aq)
balance the equation:
3 NiSO4(aq) + 2 Li3PO4(aq) Ni3(PO4)2(s) + 3 Li2SO4(aq)
3) _____ NaNO3(aq) + _____ K2SO4(aq) NR
switch ions:
NaSO4 + KNO3
both are soluble, so no reaction
4) _____ K2CrO4(aq) + _____ CaCl2(aq) switch ions: KCl + CaCrO4
charge balance products:
KCl is soluble, CaCrO4 is insoluble:
KCl(aq) + CaCrO4(s)
KCl(aq) + CaCrO4(s)
balance the equation:
K2CrO4(aq) + CaCl2(aq) 2 KCl(aq) + CaCrO4(s)
S.
1) Na2S(aq) + Pb(C2H3O2)2(aq) PbS(s) + 2 NaC2H3O2(aq)
2) K2CO3(aq) + 2 AgNO3(aq) Ag2CO3(s) + 2 KNO3(aq)
3) FeCl3(aq) + 3 NaOH(aq) Fe(OH)3(s) + 3 NaCl(aq)
4) Fe(NO3)3(aq) + NaC2H3O2(aq) NR
5) 3 Ba(NO3)2(aq) + 2 (NH4)3PO4(aq) Ba3(PO4)2(s) + 6 NH4NO3(aq)
UNIT VI - CHEMICAL EQUATIONS
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E. Combustion - general form: hydrocarbon or alcohol + O2(g) CO2(g) + H2O
* note that the products are ALWAYS CO2 and water, you just need to balance the equation
T.
1) _____ CH4(g) + _____ O2(g) CO2 + H2O
balance the equation:
•
•
CH4 + 2 O2 CO2 + 2 H2O
2) 2 C2H6 + 7 O2 4 CO2 + 6 H2O
note that if you have an even number of C’s in the hydrocarbon on the left, it can help you balance if
you begin by putting a “2” next to it immediately; remember the coefficients must be the smallest whole
numbers possible
3) 2 CH3OH + 3 O2 2 CO2
when balancing, remember the O on the alcohol as well
+ 4 H2O
S.
1)
C3H8 + 5 O2 3 CO2 + 4 H2O
2)
2 C2H2 + 5 O2 4 CO2 + 2 H2O
3)
2 C8H18 + 25 O2 16 CO2 + 18 H2O
4)
C2H5OH + 3 O2 2 CO2 + 3 H2O
V. Net Ionic Equations - show what’s really happening in a reaction
S. Name the reaction type, complete, and balance
double replacement
1. NaOH(aq) + AgNO3(aq) AgOH(s) + NaNO3(aq)
double replacement
2. NaCl(aq) + KNO3(aq) NR
double replacement
3. K2S(aq) + Pb(NO3)2(aq) PbS(s) + 2 KNO3(aq)
single replacement
4. 3 Na(s) + Cr(NO3)3(aq) 3 NaNO3(aq) + Cr
UNIT VI - CHEMICAL EQUATIONS
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B. Dissociation equations – when a soluble ionic compound dissolves in water, the ions separate
from each other and exist alone in aqueous solution
S. Write the dissociation equation for the following:
1.
NaOH(aq) Na+1(aq) + OH-1(aq)
+
2.
3.
KNO3(aq) K+1(aq) + NO3-1(aq)
K2S(aq) 2 K+1(aq) + S-2(aq)
-
+
+
-
-
+
-
+
+
-
-
C. Net Ionic equations
S. Rewrite the equations from the bottom of p. 8 showing dissociated ionic compounds in aqueous solution
* note that we know that ions can only exist in aqueous solution, so it is OK to ignore the phase
notation on ions; it is NOT OK to ignore the charges however
1.
Na+1 + OH-1 + Ag+1 + NO3-1 AgOH(s) + Na+1 + NO3-1
2.
Na+1 + Cl-1 + K+1 + NO3-1 Na+1 + NO3-1 + K+1 + Cl-1
3.
2 K+1 + S-2 + Pb+2 + 2 NO3-1 PbS(s) + 2 K+1 + 2 NO3-1
4.
3 Na(s) + Cr+3 + 3 NO3-1 3 Na+1 + 3 NO3-1 + Cr(s)
- spectator ions - ions that go unchanged in a chemical reactions; cancel out when writing the net ionic
equation see highlighted ions above; cancel them out
- net ionic equation - equation which shows a reaction without spectator ions
S. Write the net ionic equation for the above equations:
1.
Ag+1 + OH-1 AgOH(s)
2.
NR (all ions cancel out)
3.
S-2 + Pb+2 PbS(s)
4.
3 Na(s) + Cr+3 3 Na+1 + Cr(s)
UNIT VI - CHEMICAL EQUATIONS
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T. Write the net ionic equations for the following reactions (no need to balance):
1) Solid sodium is added to an aqueous solution of silver nitrate.
Overall:
w/ ions:
Net:
Na(s) + AgNO3(aq) NaNO3(aq) + Ag(s)
Na(s) + Ag+1 + NO3-1 Na+1 + NO3-1 + Ag(s)
Na(s) + Ag+1 Na+1 + Ag(s)
spectator: NO3-1
2) Aqueous solutions of iron (II) nitrate and potassium chromate are mixed.
Overall:
w/ ions:
Net:
Fe(NO3)2(aq) + K2CrO4(aq) FeCrO4(s) + 2 KNO3(aq)
Fe+2 + 2 NO3-1 + 2 K+1 + CrO4-2 FeCrO4(s) + 2 K+1 + 2 NO3-1
Fe+2 + CrO4-2 FeCrO4(s)
spectators: K+1 and NO3-1
S. Write the net ionic equations for the following reactions (no need to balance):
1) A strip of magnesium metal is placed in an aqueous solution of copper(II) sulfate.
Overall:
w/ ions:
Net:
Mg(s) + CuSO4(aq) MgSO4(aq) + Cu(s)
Mg(s) + Cu+2 + SO4-2 Mg+2 + SO4-2 + Cu(s)
Mg(s) + Cu+2 Mg+2 + Cu(s)
spectator: SO4-2
2) A pile of solid aluminum shot is placed in a beaker containing an aqueous solution of silver nitrate.
Overall:
w/ ions:
Net:
Al(s) + 3 AgNO3(aq) Al(NO3)3(aq) + 3 Ag(s)
Al(s) + 3 Ag+1 + 3 NO3-1 Al+3 + 3 NO3-1 + 3 Ag(s)
Al(s) + 3 Ag+1 Al+3 + 3 Ag(s)
spectator: NO3-1
3) Aqueous solutions of lead(II) nitrate and potassium sulfate are mixed.
Overall:
w/ ions:
Net:
Pb(NO3)2(aq) + K2SO4(aq) PbSO4(s) + 2 KNO3(aq)
Pb+2 + 2 NO3-1 + 2 K+1 + SO4-2 PbSO4(s) + 2 K+1 + 2 NO3-1
Pb+2 + SO4-2 PbSO4(s)
spectators: K+1 and NO3-1
4) Aqueous solutions of lead(II) nitrate and potassium chromate are mixed.
Overall:
w/ ions:
Net:
Pb(NO3)2(aq) + K2CrO4(aq) PbCrO4(s) + 2 KNO3(aq)
Pb+2 + 2 NO3-1 + 2 K+1 + CrO4-2 PbCrO4(s) + 2 K+1 + 2 NO3-1
Pb+2 + CrO4-2 PbCrO4(s)
spectators: K+1 and NO3-1
5) Aqueous solutions of lithium sulfide and copper(I) sulfate are mixed.
Overall:
w/ ions:
Net:
Li2S(aq) + Cu2SO4(aq) Cu2S(s) + Li2SO4(aq)
2 Li+1 + S-2 + 2 Cu+1 + SO4-2 Cu2S(s) + 2 Li+1 + SO4-2
S-2 + Cu+1 Cu2S(s)
spectators: Li+1 and SO4-2