Download Types of Chemical Reactions

Chemical Reactions, Acids and Bases
Honors Chemistry
Chemical Reactions
What is observed
What it means
1. bubbles, inflate bag, disappears, steam,
1. gas formation/release
smell, smoke
2. clear to cloudy, solid appears on bottom
2. precipitate (solid) formation
3. flame, light, temperature change
3. change in energy
4. color change
4. color change, e.g. acid-base indicator
We only know the products of a chemical reaction for sure by carrying out the reaction in the
laboratory
BUT
we can make general predictions about the products of a reaction based on “types” of
chemical reactions.
Types of Chemical Reactions
(note: not all reactions fit these categories)
1. Synthesis (or Combination)
2. Decomposition
3. Single Replacement
4. Double Replacement (or Metathesis)
5. Combustion
6. Oxidation-Reduction (Redox) (Honors)
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Chemical Reactions, Acids and Bases
Honors Chemistry
Sidebar: Energy Changes in Chemical Reactions
1.
Exothermic reaction
Releases energy (energy = one of the products)
C(s) +
O2(g)

H = -393.5 kJ
CO2(g) + 393.5 kJ
Energy diagram
C + O2
Energy
CO2
}
Energy released
(393.5 kJ)
Reactants  Products
2.
Endothermic reaction
Absorbs energy (energy = reactant)
CaCO3(s) + 176 kJ 
H = +176 kJ
CaO(s) + CO2(g)
Energy diagram
CaO + CO2
}
Energy absorbed
Energy
CaCO3
Reactants  Products
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(176 kJ)
Chemical Reactions, Acids and Bases
Honors Chemistry
Types of Chemical Reactions
1. Synthesis (Combination)
*usually produces energy - exothermic:
A + X  AX
(one product)
Examples:
a) metal + nonmetal (often oxygen)
Cu + O2  Cu2O (Copper I)
Cu + O2  CuO (Copper II)
Na + Br2  NaBr
b) nonmetal + nonmetal
N2 + O2  NO2
c) metal oxide + water  base
(Honors)
MgO + H2O  Mg(OH)2
d) nonmetal oxide + water  acid
(Honors)
CO2 + H2O  H2CO3
2. Decomposition
*usually requires energy - endothermic
AB
 or  or light
one reactant
A+B
> one product

a) compound  2 elements
Ag2O  Ag + O2

b) reactant  elements (electrolysis) (Demo: record your observations)

H2O  H2 + O2

c) metal carbonate  metal oxide + carbon dioxide (Honors)
MgCO3  MgO + CO2

d) acid  nonmetal oxide + water
H2CO3  CO2 + H2O
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(Honors)
Chemical Reactions, Acids and Bases
Honors Chemistry
Practice
•
Write balanced chemical equations for the following chemical reactions.
•
Figure out what the states of matter should be at room temperature.
•
Predict products according to the type of reaction
Synthesis:
1. carbon + oxygen 
2. gallium + oxygen 
3. nitrogen + hydrogen 
(H) 4. phosphorus (V) oxide + water 
(H) 5. calcium oxide + water 
Decomposition:
1. sodium oxide 
2. aluminum chloride 
(H) 3. calcium carbonate 
(H) 4. potassium chlorate 
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Chemical Reactions, Acids and Bases
Honors Chemistry
3. Single Replacement Reactions
A + BX  AX + B
Y + BX  BY + X
or
*Use activity series: higher replaces lower
*Use HOH for H2O
Three types of cation replacement:
a) metal replaces metal
Mg(s) + SnCl2(aq)  MgCl2(aq) + Sn(s)
b) metal replaces H in H2O
K(s) + HOH(l)  KOH(aq) + H2(g)
c) metal replaces H in acid
Fe(s) + H2SO4(aq)  FeSO4(aq) + H2(g)
Anion replacement:
Br2(l) + SrI2(aq)  SrBr2(aq) + I2(s)
halogen replaces halogen
Demonstration – Single Replacement
Use the activity series on your reference sheet to predict the products of the following
reactions:
Cu(s) + AgNO3(aq)

Ag(s) + Cu(NO3)2(aq) 
Practice
1. For each of the following pairs of elements, circle the one that would replace the other
element in a compound.
a. calcium, tin
e. iron, copper
b. bromine, fluorine
f. iodine, chlorine
c. aluminum, potassium
g. silver, lead
d. zinc, calcium
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Chemical Reactions, Acids and Bases
Honors Chemistry
2. For each of the following reactants, use the activity series to determine whether the
reaction would take place or not. If no reaction takes place, write NR in the blank. If a
reaction does take place, write the formulas for the products of the reaction. (Hint: If
an active metal replaces the hydrogen in water, the hydroxide of the active metal
forms. H-OH)
a. Li(s) + Fe(NO3)3(aq)  _________
b. Au(s) + HCl(aq)  __________
c. Cl2(g) + KBr(aq)  ___________
d. Cu(s) + Al(NO3)3(aq)  ________
e. Ag(s) + HBr(aq)  _________
f. Ni(s) + SnCl2(aq)  ___________
3.
Magnesium metal can be used to remove tarnish from silver items. Silver tarnish is
the corrosion that occurs when silver metal reacts with substances in the environment,
especially those containing sulfur. Why would magnesium remove tarnish from silver?
4.
Use the activity series for metals to explain why copper metal is used in plumbing
where the water might contain compounds of many different metals.
5.
The last four metals in the activity series of metals are commonly referred to as the
“coinage metals”. Why would these metals be chosen over more active metals for use
in coins? Why do you think some more active metals, such as zinc or nickel, are
sometimes used in coins?
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Chemical Reactions, Acids and Bases
Honors Chemistry
4. Double Replacement
AX + BY  BX + AY
(aq) (aq) (aq) forms: ppt
H2O
gas
}
a) ppt-forming:
If both products are aqueous  NR
If not, NR*
Pb(NO3)2(aq) + KI(aq)  KNO3(aq) + PbI2(s)
(Use SolubilitiesTable to predict products – see reference sheet)
b) water-forming:
H2SO4(aq) + NaOH(aq)  Na2SO4(aq) + H2O(l)
acid

+ base
salt
+ water
c) gas-forming (e.g. CO2 from a 2o decomposition rxn)
NaHCO3(aq) + HC2H3O2(aq)  NaC2H3O2(aq) + H2O(l) + CO2(g)
Practice – Single Replacement and Double Replacement Reactions
Use the activity series or solubility table to predict the product of the following reactions:
Na(s) + SrBr2(aq) 
CrI3(aq) + KCl(aq) 
Zn(s) + H2SO3(aq) 
K2CO3(aq) + HI(aq) 
Na(s) + H2O(l) 
HC2H3O2(aq) + (NH4)2S(aq) 
Fe(s) + CuCl2(aq) 
HBr(aq) + Ba(OH)2(aq) 
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Chemical Reactions, Acids and Bases
Honors Chemistry
5. Combustion: Hydrocarbon + oxygen  carbon dioxide + water
a)
complete - forms CO2 + H2O:
CH4 + O2  CO2 + H2O + Energy
b)
incomplete - forms CO + H2O:
CH4 + O2  CO + H2O + Energy (Honors)
Balancing Combustion Reactions
e.g. C2H2 + O2  CO2 + H2O
1. Balance hydrogens, but at the same time make the number of oxygens in H2O even by
doubling the coefficient if necessary – do NOT balance the oxygens at this point!
(i.e. make the number of Hs in the reactants divisible by 4)
C2H2 + O2  CO2 + H2O
2 C2H2 + O2  CO2 + 2 H2O
2. Balance carbons
2 C2H2 + O2  4 CO2 + 2 H2O
3. Lastly, balance the oxygen molecules on the left
2 C2H2 + 5 O2  4 CO2 + 2 H2O
2 C2H2 + 5 O2  4 CO2 + 2 H2O
Practice
Write balanced chemical equations for the complete combustion of
•
propane (C3H8)
•
pentane (C5H12)
•
hexane (C6H14)
•
decane (C10H22)
•
ethyl alcohol (C2H5OH)
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Chemical Reactions, Acids and Bases
Honors Chemistry
Total and Net Ionic Equations
• Balanced Formula Equation:
2 KOH(aq) + H2SO4(aq)  K2SO4(aq) + H2O(l)
• Total Ionic Equation:
2 K+ + 2 OH-(aq) + 2 H+ + SO42-(aq) 2 K+ + SO42-(aq) + 2 H2O(l)
• Net Ionic Equation:
2 OH-(aq) + 2 H+  H2O(l)
1. What is a spectator ion?
2. What are the spectator ions in this reaction?
3. Compare and contrast each pair below.
a. balanced formula equations, total ionic equations
b. total ionic equations, net ionic equations
4. For the reaction between aqueous silver nitrate and aqueous sodium chloride, write
each of the following. The products of the reaction are aqueous sodium nitrate and
solid silver chloride.
a. balanced formula equation
b. total ionic equation
c. net ionic equation
5. What is the net ionic equation for the reaction between aqueous calcium
hydroxide and nitric acid? The products of this reaction are aqueous calcium nitrate
and water. How does this net ionic equation compare to the net ionic equation shown
at the top of this page? Hint: you may want to begin with the balanced formula
equation, then total ionic equation.)
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Chemical Reactions, Acids and Bases
Honors Chemistry
6. Oxidation-Reduction (Redox) Reactions
Electrons are transferred from one atom to another.
Note that when one substance is oxidized, another compound must be reduced, and viceversa.
Oxidation = - electrons from a substance
Reduction = + electrons to a substance
Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g)
0
+1 -1
+2 -1
0
•
•
•
Note: The transfer of electrons during oxidation-reduction reactions often produce
energy (when spontaneous), which can be in the form of electricity.
LEO the lion says GER (Loss of Electrons = Oxidation/Gain of Electrons = Reduction)
OIL RIG (oxidation is loss and reduction is gain)
Examples:
a)
Combustion: “rapid oxidation reaction in which a large amount of heat and
usually light are released”
C + O2  CO2, CO
S + O2  SO2
What was oxidized?
What was reduced?
b)
Metal + acid (SR): e.g.
Zn(s) + 2 HCl(aq)  ZnCl2(aq) + H2(g)
Total ionic equation:
What was oxidized?
What was reduced?
c)
Metal + salt (SR): e.g.
Mg(s) + CoSO4(aq)  MgSO4(aq) + Co(s)
Total ionic equation:
What was oxidized?
What was reduced?
Oxidation numbers help us keep track of what happens to the electrons in reactions.
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Chemical Reactions, Acids and Bases
Honors Chemistry
Practice
Identify redox pairs and oxidation numbers.
Write net ionic equations for the following reactions.
2 Na(s) + SrBr2(aq)  Sr(s) + 2 NaBr(aq)
Zn(s) + H2SO3(aq)  ZnSO3(aq) + H2(g)
2 Na(s) + 2 H2O(l)  2 NaOH(aq) + H2(g)
Fe(s) + CuCl2(aq)  Cu(s) + FeCl2(aq)
Predicting Products of Different Reaction Types
Class of reaction
Synthesis
Decomposition
Reactants
two or more substances
one compound
Single Replacement
a metal and a compound
Double Replacement
a nonmetal (halogen) and a
compound
two compounds dissolved in
water
hydrocarbon + oxygen
Combustion
(restricted definition)
Oxidation-Reduction
(Honors)
one or more substances
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Probable Products
Chemical Reactions, Acids and Bases
1.
Honors Chemistry
For each set of reactants listed below, identify the type of reaction that the reactants
might undergo. List as many reaction types as may apply. Assume that all the
reactants for the reaction are listed.
a. a compound and an element
b. two compounds
c. one compound
2. For each set of reactant products listed below, identify the type of reaction that might
have formed the products. List as many reaction types as may apply. Assume that all
the productions for the reaction are listed.
a. a compound and an element
b. two compounds
c. one compound
3. Classify each of the following examples according to the type of reaction involved.
List as many reaction types as may apply.
a. A match burns
b. The carbonic acid found in soft drinks breaks down into bubbles of carbon dioxide
and water
c. Phosphorus and oxygen react rapidly, forming diphosphorus pentoxide
d. An iron nail is placed into a copper sulfate solution.
Copper metal appears on the nail.
e. The acid in baking powder reacts with baking soda (NaHCO3), forming carbon
dioxide gas and other products.
f. Water and sulfur trioxide react to form sulfuric acid.
g. Copper wire is placed in a silver nitrate solution. The solution turns blue, which is
the color of the copper ion, and solid silver forms on the wire.
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Chemical Reactions, Acids and Bases
Honors Chemistry
Properties of Acids and Bases
When dissolved in water:
Acids
Bases
taste sour
taste bitter
feel wet
feel slippery
turn blue litmus paper pink/red
turn red litmus paper blue
conduct electricity
conduct electricity
react with most metals
do not react with most metals
contain more H+ than OH-
contain more OH- than H+
pH < 7
pH > 7
Strong acid + strong base  salt + H2O
Arrhenius (traditional) acids and bases (C19th)
Acid: compound containing H that ionizes to yield H+ in solution
HCl(g)
H2O
 H+(aq) + Cl-(aq)
or
HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq)
Base: compound containing OH that ionizes to yield OH- in solution
H2O
NaOH(s)  Na+(aq) + OH-(aq)
Autoionization of water:
H2O + H2O  H3O+ + OHIn pure water: [H3O+] = 1.0 x 10-7 M and [OH-] = 1.0 x 10-7 M
If we add acid [H3O+] increases and [OH-] decreases
[H3O+] = 1.0 x 10-4 M
[OH-] = 1.0 x 10-10 M
If we add base, the reverse is true:
[H3O+] = 1.0 x 10-4 M
[OH-] = 1.0 x 10-10 M
What is the product of [H3O+][OH-] in each case?
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Chemical Reactions, Acids and Bases
Honors Chemistry
pH = - log [H+]
pOH = - log [OH-]
= - log (1.0 x 10-7)
= - log (1.0 x 10-7)
= -(-7)
= -(-7)
=7
=7
basis of neutral pH 7: [H+] = [OH-]
Concentration, pH and pOH
Concentration is given in terms of molarity (M)
Concentration of H+ = [H+] = = 0.0100 mol H+
= 0.0100 M H+
L
In scientific notation [H+] = 1.00 x 10-2 M
Find pH: pH = - log [H+]
pH = 2
Find pOH: pOH = - log [OH-] and pH + pOH
pOH = 12
Find [OH-]: [OH-] = 10-pOH = 10-12
[OH-] = 1.00 x 10-12 M
Converting between concentration and pH (from slide)
Practice
pH + pOH = 14; pH = -log[H+]; pOH = -log[OH-]
When pH = 2
When pOH = 8
[H+] = _______ M
[OH-] = ______M
pOH = _______
pH = _______
[OH-] = ______ M
[H+] = _______ M
[H+] = 1.0 x 10-3 M. What is the [OH-]? _____________
More Practice
1. What is the pH of a solution with a [H+] of 10-8 M? ________
2. What is the pOH of a solution with a [OH-] of 10-11 M? ________
3. What is the pH of a solution with a [OH-] of 10-2 M? ________
4. What is the pOH of a solution with a [H+] = 10-5 M? ________
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Chemical Reactions, Acids and Bases
Honors Chemistry
5. Which is more acidic, a solution with a pH of 6 or one with a pH of 9? __________
6. Which is more basic, a solution with a pOH of 7 or one with a pOH of 12? _________
7. Which is more acidic, a solution with a pH of 5 or one with a pOH of 10? ______
8. Which is more basic, a solution with a pH of 8 or one with a pOH of 12? _____
9. Stomach contents can have a pH of 3. Are stomach contents acidic, basic or neutral?
_______
10. Pure water has a pOH of 7. Is pure water acidic, basic or neutral? __________
11. Normal rain has a pH of approximately 6. Is normal rain strongly acidic, slightly acidic,
neutral, slightly basic, or strongly basic? ________
12. Acid precipitation is often a problem in industrialized areas.
What might you expect the pH of acid rain to be? _______________________
Strengths of Acids and Bases
Strong acid or base – ionizes/dissociates completely in water
[H+] or [OH-] = conc. of acid or base.
e.g. HCl, NaOH.
5 units of acid – 5 out of 5 dissociated: H+
Cl-
H+
Cl- H+
Cl-
H+
Cl- H+
Cl-
Weak acid or base – ionizes/dissociates only partially in water
[H+] or [OH-] < conc. of acid or base.
e.g. HC2H3O2, NH3
5 units – only 1 out of 5 dissociated: HC2H3O2 HC2H3O2 HC2H3O2 HC2H3O2
Strong concentrated
Weak dilute
Strong acid:
Strong base:
HCl + H2O  H3O+ + Cl-
H2O
NaOH  Na+ + OH-
1.0 x 10-2 M
?M
?M
1.0 x 10-2 M
pH = ?
?M
pH = ?
Weak base:
Weak acid:
HC2H3O2 + H2O  H3O+ + C2H3O21.0 x 10-2 M
NH3 + H2O  NH4+ + OH1.0 x 10-2 M
?M
?M
pH = ?
pH = ?
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H+ C2H3O2-
Chemical Reactions, Acids and Bases
Honors Chemistry
Demo - Strong and Dilute vs. Weak and Concentrated Acids and Bases
Acids:
Strong HCl
Weak HC2H3O2
Weak HC2H3O2
Dilute
Dilute
Concentrated
0.01 M
0.01 M
1M
pH =
pH =
pH =
Strong NaOH
Weak NH3
Weak NH3
Dilute
Dilute
Concentrated
0.01 M
0.01 M
1M
pH =
pH =
pH =
Bases:
What do you think?
Are the following acidic, basic or neutral?
table salt
vinegar
rubbing alcohol
window cleaner
distilled water
lemon juice
soap
drain cleaner
applesauce
blood
What is the difference between a strong acid and a concentrated acid?
A weak acid and a dilute acid?
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