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Chapter 7: Chemical Reactions
Read Chapter 7 and Check MasteringChemistry due dates.
Evidence of Chemical Reactions:
Changes occur in the chemical composition
Color change
Formation of solid
Formation of gas
Emission of light
Change in temperature without
externally adding or removing heat.
Try this #1: Are you fooled into thinking all
changes are evidence of chemical reactions
Is boiling water (liquid to gas) a chemical change?
Is separation of CuSO4 from sand by dissolving the CuSO4 in water and filtering the sand a chemical change?
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The Chemical Equation:
Reactants Products
Phases: solid (s), liquid (l), gas (g), aqueous (aq)
Balancing Chemical Equations:
Balance the same number of atoms on either side
Total charges must also balance on each side
Once the formulas are correctly written, add numbers to coefficients (never change a
subscript to balance)
Process:
Write skeletal equation with correct chemical formulas as reactants and
products
Start with a substance with the most atoms and subscripts
If an element occurs in only one compound on both sides, that element
should be balanced first.
If more than one choice is available, balance metals before nonmetals
Balance a free element last, adjust the coefficient on the fee element
Remove fractions by multiplying through by the denominator
Check
The number of a particular type of atom within a chemical formula
embedded in an equation is obtained by multiplying the subscript for
the atom by the coefficient for the chemical formula.
If there is no coefficient or subscript, a 1 is implied.
An example of the balanced equation for the combustion of natural
gas follows:
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Try this #2:
Practice balancing the following:
a) carbon dioxide gas and water forms carbonic acid
b) C3H8 (g) + O2 (g) CO2 (g) + H2O (l)
c) Pb(NO3)2 (aq) + K2S (aq) PbS (s) + KNO3 (aq)
d) solid zinc is added to hydrochloric acid to produce hydrogen gas and
aqueous zinc chloride
e) NH3 (g) + O2 (g) NO2 (g) + H2O (l)
f) aqueous acetic acid and potassium sulfite react to form aqueous potassium
acetate, water and sulfur dioxide gas.
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Electrolytes in Aqueous Solution:
Pure water does not conduct electricity.
If charged ions are dissolved in water it will conduct
electricity.
Strong Electrolytes will dissociate into its ions in an
aqueous solution and are written as separated ions in
the total and net ionic reactions.
Examples: Strong acids, Strong Bases, Soluble salts.
Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3
Strong Bases: soluble hydroxides from Group IA (not including H) and
Group IIA, not including the top two: LiOH, NaOH, KOH, RbOH,
Ca(OH)2, Sr(OH)2, Ba(OH)2
Soluble Salts:
Ionic compounds that contain cations from Group 1A; Li+, Na+, K+, or
NH4+ or the anions NO3
-1, ClO4-1, C2H3O2
-1 are mostly soluble.
Compounds with Cl-1, Br-1, I-1 are soluble except with Ag+, Hg2+2, Pb+2
Compounds with SO4-2 are soluble except Sr+2, Ba+2, Pb+2 or Ca+2.
Weak Electrolytes will partially dissociate into its ions in an aqueous solution, but are
written together in an ionic equation. Weak electrolytes are the weak acids and
weak bases such as HC2H3O2 or NH3
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Nonelectrolytes will stay together in an aqueous solution. Nonelectrolytes are the
insoluble salts [solids], and molecular gases and liquids.
Solubility Rules: familiarize yourself with the top portion of ions mostly soluble
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Writing Molecular, Ionic, and Net ionic equations:
Example: For the double displacement reaction of lead (II) nitrate reacting with potassium iodide.
Whole equation: Balanced
Pb(NO3)2 (aq) + 2 KI (aq) PbI2 (s) + 2 KNO3 (aq)
Total ionic equation:
Pb+2(aq) + 2 NO3-1
(aq) + 2 K+1(aq) + 2 I-1
(aq) PbI2 (s) + 2 K+1(aq) + 2 NO3
-1(aq)
Identify the spectator ions and leave them out when writing the net ionic eq.
Net ionic equation:
Pb+2 (aq) + 2 I-1 (aq) PbI2 (s)
This is a double displacement reaction and specifically a precipitation reaction.
(D-D) double displacement type reactions: AB + CD AD + CB
A chemical composition change has occurred. The visible evidence of this change is the
formation of yellow solid. Two colorless liquids react to form the new yellow solid PbI2.
Try this #3:
Follow the rules above to write the Molecular, Ionic, and Net ionic equations for the
reaction of aqueous calcium chloride and aqueous potassium carbonate.
Whole equation:
Total ionic equation:
Identify the spectator ions and leave them out when writing the net ionic eq.
Net ionic equation
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Classifying Chemical Reaction Types:
(D-D) double displacement
(N) neutralization or acid-base,
(P) precipitation
(R) redox or oxidation-reduction
(SR) single replacement
(C) combustion
(G) gas evolution
(Syn) synthesis or combination
(D) decomposition
Classifying and Predicting Products and Chemical Reactions:
The following examples will help you classify the type of reaction and predict the
expected products.
(D-D) double displacement: AB + CD AD + CB
A double displacement reaction starts with two ionic compounds in which the ions
exchange to produce new balanced ionic compounds. Always write the cation
before the anion and verify that the net charge of each compound is zero. Ionic
compounds may be acid, base, or salt. Oxidation charges do not alter in double
displacement reactions so this type will never be a redox reaction.
Driving forces for double displacement reactions include
formation of a solid (P) Precipitation, Check solubility rules
formation of water (N) Neutralization or Acid-Base Reaction
formation of a weak electrolyte (WE)
Reactions do not always occur when mixing two aqueous solutions. (NR) no reaction
(P) Formation of a new solid in a double displacement reaction when there is
no solid on the reactant side is called PRECIPITATION.
Ni(NO3)2 (aq) + Na2S (aq) NiS (s) + 2 NaNO3 (aq) DD,P
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(N) Formation of water in a double displacement reaction is called
NEUTRALIZATION (also known as Acid-Base reaction)
3 KOH (aq) + H3PO4(aq) K3PO4 (aq) + 3 H2O (l) DD,N
(WE) Formation of a WEAK ELECTROLYTE, generally a weak acid, produced
from a double displacement reaction
Al(C2H3O2)3 (aq) + 3 HCl (aq) AlCl3 (aq) + 3 HC2H3O2 (aq) DD,WE
(NR) When all ionic products are strong electrolytes, there is NO REACTION.
FeBr3 (aq) + 3 LiNO3 (aq) 3LiBr (aq) + Fe(NO3)3 (aq) NR
(G) Gas Evolution:
Several common compounds are in the gas phase. You should recognize the
following as gases.
CO2, SO2, CH4, NH3, H2S, H2, N2, O2, F2, Cl2, NO, NO2
Special cases of (G) Gas Evolution in (DD) Double Displacement:
There are three common products that further decompose leading to three products
in place of just the two products in a double displacement reaction. They are as
follows.
NH4OH (aq) NH3 (g) + H2O (l)
H2SO3 (aq) SO2 (g) + H2O (l)
H2CO3 (aq) CO2 (g) + H2O (l)
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The double displacement reactions below show examples of the decomposition of
one of the ionic products. The driving forces include both formation of water and a
gas, because water is formed these can be labeled Neutralization reactions. The last
one is DD, N, and P.
K2CO3 (aq) + 2HCl (aq) H2CO3 (aq) + 2 KCl (aq)
K2CO3 (aq) + 2HCl (aq) CO2 (g) + H2O (l) + 2 KCl (aq)
Na2SO3 (aq) + 2HCl (aq) H2SO3 (aq) + 2 NaCl (aq)
Na2SO3 (aq) + 2HCl (aq) SO2 (g) + H2O (l) + 2 NaCl (aq)
(NH4)2SO4 (aq) + Ba(OH)2 (aq) 2 NH4OH (aq) + BaSO4 (s)
(NH4)2SO4 (aq) + Ba(OH)2 (aq) 2 NH3 (g) + 2 H2O (l) + BaSO4 (s)
Try this #4:
Write an equation for the precipitation reaction that occurs (if any) when
solutions of sodium carbonate Na2CO3(aq) and copper(II) chloride CuCl2(aq)
are mixed.
Predict the products and balance for the reaction that geologist use to test for
carbonates in rock or mineral samples…
HNO3 (aq) + CaCO3 (s)
(marble)
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(Syn) Synthesis or combination: A + B AB
A synthesis reaction starts with two or more substances and creates a single
compound product. The reverse of a synthesis reaction is Decomposition.
Remember which elements are diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2. Know
the elements in their pure form: gas (red), solid (black), and liquid (blue), by color
on the periodic table in the classroom.
a) two elements (metal plus nonmetal) ionic compound.
Na (s) + Cl2 (g) NaCl (s) Balance this
b) metal oxide and water base (metal hydroxide)
BaO (g) + H2O (l) Ba(OH)2 (aq)
c) nonmetal oxide and water acid
CO2 (g) + H2O (l) H2CO3 (aq)
Try this #5:
Balance the synthesis reactions…
Al (s) + O2 (g) Al2O3 (s)
Na2O (s) + H2O (l) NaOH (aq)
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(D) Decomposition: AB A + B
A decomposition reaction starts with one reactant and breaks up into two or more
substances. The reverse of a decomposition reaction is synthesis. Remember the
diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2.
a) Water can be broken into its elements by electrolysis
b) ionic compound two elements (metal plus nonmetal)
2 Fe2O3 (s) 4 Fe (s) + 3 O2 (g)
c) metal carbonate metal oxide and carbon dioxide
CaCO3 (s) CaO (s) + CO2 (g)
d) metal bicarbonate metal carbonate + water + carbon dioxide
2 Al(HCO3)3 (s) Al2(CO3)3 (s) + 3 H2O (l) + 3 CO2 (g)
e) metal connected to halogen with oxygen metal halide + oxygen
Ca(BrO3)2 (s) CaBr2 (s) + 3 O2 (g)
f) hydrated salt anhydrous salt plus water
CuSO4.5H2O (s) CuSO4 (s) + 5 H2O (l)
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Try this #6:
Balance the decomposition reactions that occur after heating…
CoCl2.6H2O (s) CoCl2
(s) + 6H2O (l)
KClO3 (s) KCl (s) + O2 (g)
NaHCO3 (s) Na2CO3 (s) + H2O (l) + CO2 (g)
(R) Redox or oxidation-reduction reactions:
Redox reactions transfer electrons. A way to tell that a redox reaction takes place is
to check for element charges and see if they change from reactant side to product
side. If on one side of the reaction an atom or molecule has a zero charged element
and on the other side of the reaction the same atom is now part of a compound or an
ion, then electrons have been moved. Some synthesis and decomposition reactions
are redox. All combustion and single replacement reactions are redox reactions.
Oxidation Reduction
increases oxidation number reduces oxidation number
lose electrons gain electrons
2 Cl-1 Cl2 + 2 e- K+ + 1 e- K
OIL RIG
Oxidation is losing electrons reduction is gaining electrons
Leo the lion growls Ger
Lose electrons is oxidation gain electrons is reduction
(C) Combustion: elements burn with O2 gas to produce oxides,
Common products include: CO2, H2O, NO2, SO2.
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l)
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Try this #7:
Predict the products and balance
C4H10 (l) + O2 (g)
C6H14S (s) + O2 (g)
C12H22O11 (s) + O2 (g)
NH3 (g) + O2 (g)
Another Redox [Oxidation-Reduction] type reaction: Chem 12: identify classification or
balance, but not necessary to predict the products for this class.
(SR) Single Replacement: A + BC AC + B
The more active element will have a partner, less active is alone.
Activity series:
Au<Hg<Ag<Cu<H2<Pb<Sn<Ni<Fe<Cr< Zn<Mn<Al< Mg< Na<Ca< K<Li
Try this #8:
Predict the products if a reaction occurs or write NR for no reaction…
Zn(NO3)2 (aq) + Cu (s)
Cu(NO3)2 (aq) + Zn (s)
Redox Applications: Combustion, Bleaching, Batteries, Fuel cells, Metallurgy, Corrosion, Respiration
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Practice Problems:
1. List the elements that are diatomic.
2. Name several driving forces for a chemical reaction.
3. Name several signs of evidence that would indicate a chemical reaction happened.
4. What information can one obtain from a balanced chemical equation?
5. For the following double-displacement reaction:
a) Complete the whole equation by including the products and balance the
equation. Include the physical states in all the equations.
NaCl (aq) + AgNO3 (aq)
b) Write the balanced total ionic equation for the above reaction. Include
charges on ions.
Circle the spectator ions in part b?
c) Write the balanced net ionic equation for this reaction.
d) What is/are the driving force(s) for this reaction?
6. Crude gunpowders often contain a mixture of solid potassium nitrate and charcoal
(solid carbon). When such a mixture is heated until a reaction occurs, a solid residue
of potassium carbonate is produced. The explosive force of the gunpowder comes
from the fact that two gases are also produced, carbon monoxide and nitrogen,
which increase in volume with great force and speed. Write the balanced chemical
equation for the reaction.
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7. Balance and Classify in as many ways possible the following reactions.
Possible classifications:
(D-D) double displacement
(N) neutralization or acid-base,
(P) precipitation
(R) redox or oxidation-reduction
(SR) single replacement
(C) combustion
(G) gas evolution
(Syn) synthesis or combination
(D) decomposition
(NR) no reaction
a) Mg(ClO3)2 (s) MgCl2 (s) + O2 (g)
b) N2 (g) + O2 (g) N2O5 (g)
c) C6H6 (l) + O2 (g) CO2 (g) + H2O (g)
d) KOH (aq) + H2SO4(aq) K2SO4 (aq) + H2O (l)
e) AgNO3 (aq) + Na2CrO4 (aq) Ag2CrO4 (s) + NaNO3 (aq)
f) aqueous silver nitrate and solid copper reacts to form aqueous copper (II)
nitrate and solid silver.
g) solid magnesium carbonate heated produces carbon dioxide gas and solid
magnesium oxide
h) C3H8 (g) + O2 (g) CO2 (g) + H2O (g)
i) Fe (s) + Br2 (l) FeBr3 (s)
j) H2SO4(aq) + Na2CO3(aq) Na2SO4(aq) + H2O(l) + CO2(g)
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k) Al2(CO3)3 (s) Al2O3 (s) + CO2 (g)
l) HC2H3O2 (aq) + Mg (s) H2 (g) + Mg(C2H3O2)2(aq)
m) Ni(NO3)2 (aq) + K2S (aq) NiS (s) + KNO3 (aq)
n) KOH (aq) + (NH4)2SO4(aq) NH3 (g) + K2SO4(aq) + H2O (l)
o) Al (s) + O2 (g) Al2O3 (s)
p) Fe(ClO3)3 (s) FeCl3 (s) + O2 (g)
q) Ag (s) + HI (aq) AgI (s) + H2 (g)
r) H2O (l) + N2O3 (g) HNO2 (aq)
s) aqueous sodium hydroxide and sulfuric acid react to form aqueous sodium
sulfate and liquid water
t) octane gas and oxygen gas react to form carbon dioxide gas and water.
u) aqueous potassium sulfide and lead II nitrate react to produce solid lead II
sulfide and aqueous potassium nitrate.
v) Aqueous nitric acid is added to aqueous sodium bicarbonate, the reaction
produces an aqueous salt, plus a gas and a liquid.
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8. Complete and Balance the following chemical reactions.
Include the state that the substances are in, (s), (l), (g), or (aq). If no reaction in a
double displacement then write No reaction.
a) Combustion reaction:
C7H16 (s) + O2 (g)
b) Double Displacement reaction:
aqueous sodium hydroxide is added to aqueous copper (II) chloride
c) Double Displacement reaction:
aqueous sulfuric acid is added to aqueous ammonium carbonate
d) Double displacement reaction:
KNO3 (aq) + NH4Br (aq)
e) Double Displacement reaction:
HCl (aq) + Ba(OH)2 (aq)
f) Combustion
Liquid pentane, C5H12, reacts with atmospheric oxygen