Date post: | 02-Jan-2016 |
Category: |
Documents |
Upload: | lizbeth-smith |
View: | 221 times |
Download: | 4 times |
Chapter 7ChemicalReactions
Day One and Two
Tro's "Introductory Chemistry", Chapter 7 2
Day Three
Tro's "Introductory Chemistry", Chapter 7 3
Chemical Reactions Reactions:
chemical changes in matter resulting in new substances
Reactions involve rearrangement and exchange of atoms to produce new moleculesElements DO NOT CHANGE during a reaction.
Atoms of different elements can combine to make new compounds
Molecules can decompose into smaller molecules or atoms
Atoms can gain or lose electrons, turning them into ions.○ Or changing the charge on ions that are already there.
Tro's "Introductory Chemistry", Chapter 7 4
Combustion Reactions Reactions in which O2 is consumed by combining
with another substance are called combustion reactions.
5
Reactants Products
Precipitation Reactions
Combining of ions resulting in formation of a material that is insoluble in water: precipitation reactions
Tro's "Introductory Chemistry", Chapter 7 6
Evidence of Chemical Reactions
Look for evidence of a new substance Visual clues (permanent)
Color change Precipitate formation
○ Solid that forms when liquid solutions are mixedGas bubblesLarge energy changes
○ Container becomes very hot or cold○ Emission of light
Other clues.New odor Whooshing sound from a tube Permanent new state
Tro's "Introductory Chemistry", Chapter 7 7
Evidence of Chemical Change
8Tro's "Introductory Chemistry", Chapter 7
Color Change
Formation of Solid PrecipitateFormation of a Gas
Emission of LightRelease or Absorption of Heat
Practice—Decide Whether Each of the Following Involve a Chemical Reaction.
Tro's "Introductory Chemistry", Chapter 7 9
• Photosynthesis
• Heating sugar until it turns black
• Heating ice until it turns liquid
• Digestion of food
• Dissolving sugar in water
Yes, CO2 and H2O combine into carbohydrates
Yes, sugar decomposing
No, molecules still same
Yes, food decomposing and combiningwith stomach acid
No, molecules still same
Chemical Equations
Short-hand way of describing a reaction. Provides information about the reaction.
Formulas of reactants and products.States of reactants and products.Relative numbers of reactant and product
molecules that are required.Can be used to determine masses of
reactants used and products that can be made.
Tro's "Introductory Chemistry", Chapter 7 10
Conservation of Mass
Matter cannot be created or destroyed.Therefore, the total mass cannot change.mass of reactants = total mass of products.
In a chemical reaction, all the atoms present at the beginning are still present at the end.If all the atoms are still there, then the mass
will not change.
Tro's "Introductory Chemistry", Chapter 7 11
The Combustion of Methane
Methane gas burns to produce carbon dioxide gas and gaseous water.Whenever something burns it combines with
O2(g).
Tro's "Introductory Chemistry", Chapter 7 12
Combustion of Methane Methane gas burns to produce carbon dioxide gas
and gaseous water.Whenever something burns it combines with O2(g).
CH4(g) + O2(g) CO2(g) + H2O(g)
Assignment
Problem Set #1 Page 232
○ #29- 33
Tro's "Introductory Chemistry", Chapter 7 14
Day Four
Tro's "Introductory Chemistry", Chapter 7 15
Chemical Equations
CH4 and O2 are the reactants, and CO2 and H2O are the products.
The (g) after the formulas tells us the state of the chemical.
The number in front of each substance tells us the numbers of those molecules in the reaction.Called the coefficients.
Tro's "Introductory Chemistry", Chapter 7 16
CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)
Symbols Used in Equations Symbols used to indicate state after
chemical.(g) = gas; (l) = liquid; (s) = solid.(aq) = aqueous = dissolved in water.
Energy symbols used above the arrow for decomposition reactions. = heat. h = light.shock = mechanical.elec = electrical.
Tro's "Introductory Chemistry", Chapter 7 17
Balancing Equations
1. Write the CORRECT formulas for each compound (silicon dioxide + carbon silicon carbide + carbon monoxide)
2. If element occurs in only one compound balance first. Balance METALS first.
Tro's "Introductory Chemistry", Chapter 7 18
Balancing Equations, cont.
3. If element occurs as a FREE element, balance LAST.
4. Check to make sure equation is balanced.
Tro's "Introductory Chemistry", Chapter 7 19
SiO2 + C SiC + CO
Example When magnesium metal burns in
air, it produces a white, powdery compound magnesium oxide.
1. Write a skeletal equation
2. Count the number of atoms on each side.
Mg O
Tro's "Introductory Chemistry", Chapter 7 20
Another Example Under appropriate conditions at 1000°C, ammonia gas
reacts with oxygen gas to produce gaseous nitrogen monoxide and steam
Tro's "Introductory Chemistry", Chapter 7 21
Practice #1When aluminum metal reacts with air, it produces a white, powdery compound called aluminum oxide.
Tro's "Introductory Chemistry", Chapter 7 22
Practice #2Acetic acid reacts with the metal aluminum to make aqueous aluminum acetate and gaseous hydrogen.Acids are always aqueous.Metals are solid except for mercury.
Tro's "Introductory Chemistry", Chapter 7 23
Practice #3Combustion of ethyl alcohol (C2H5OH) in flambé (a brandied flaming dessert).
Tro's "Introductory Chemistry", Chapter 7 24
Practice #4Combustion of liquid butane (C4H10) in a lighter.
C4H10(l) + O2(g) CO2(g) + H2O(g)
Tro's "Introductory Chemistry", Chapter 7 25
Assignment
Problem Set #2 Page 233
○ #37, 38, 39
Tro's "Introductory Chemistry", Chapter 7 26
Day Five
Tro's "Introductory Chemistry", Chapter 7 27
Aqueous Solutions Chemicals we are react together are most of
the time dissolved in waterMixtures of a chemical dissolved in water are
called aqueous solutions Dissolving the chemicals in water helps them
to react together fasterThe water separates the chemicals into individual
molecules or ionsThe separate, free-floating particles come in
contact more frequently so the reaction speeds up
Tro's "Introductory Chemistry", Chapter 7 28
Predicting Whether a Reaction Will Occur in Aqueous Solution
“Forces” that drive a reaction: Formation of a solid. Formation of water. Formation of a gas. Transfer of electrons.
When chemicals (dissolved in water) are mixed and one of the above-noted forces occur, the reaction will generally happen.
Tro's "Introductory Chemistry", Chapter 7 29
Dissociation When ionic compounds
dissolve in water, the anions and cations are separated from each other. This is called dissociation.However, not all ionic
compounds are soluble in water!
When compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion.
Tro's "Introductory Chemistry", Chapter 7 30
Dissociation, Continued Potassium iodide dissociates in water into
potassium cations and iodide anions.
KI(aq) → K+1(aq) + I-1(aq)
Copper(II) sulfate dissociates in water into copper(II) cations and sulfate anions.
CuSO4(aq) → Cu+2(aq) + SO4-2(aq)
Tro's "Introductory Chemistry", Chapter 7 31
K+1 I-1K I
Cu+2 SO4-2Cu SO4
Dissociation, Continued
Potassium sulfate dissociates in water into potassium cations and sulfate anions.
K2SO4(aq) → 2 K+1(aq) + SO4-2(aq)
Tro's "Introductory Chemistry", Chapter 7 32
K+1
SO4-2
K+1
KK SO4
Electrolytes
Electrolytes are substances whose water solution is a conductor of electricity
All electrolytes have ions dissolved in water
Tro's "Introductory Chemistry", Chapter 7 33
Electrolytes, Continued
In strong electrolytes, all the electrolyte molecules or formula units are separated into ions
In nonelectrolytes, none of the molecules are separated into ions
In weak electrolytes, a small percentage of the molecules are separated into ions
Tro's "Introductory Chemistry", Chapter 7 34
Types of Electrolytes Salts = Water soluble ionic compounds.
All strong electrolytes.
Acids = Form H+1 ions and anions in water solution.In binary acids, the anion is monoatomic. In oxyacids, the
anion is polyatomic.Sour taste.React and dissolve many metals. Strong acid = strong electrolyte, weak acid = weak electrolyte.
Bases = Water-soluble metal hydroxides.Bitter taste, slippery (soapy) feeling solutions.Increases the OH-1 concentration.
Tro's "Introductory Chemistry", Chapter 7 35
When Will a Salt Dissolve? A compound is soluble in a
liquid if it dissolves in that liquid.NaCl is soluble in water, but
AgCl is not. A compound is insoluble if
a significant amount does not dissolve in that liquid.AgCl is insoluble in water.
○ Though there is a very small amount dissolved, but not enough to be significant.
Tro's "Introductory Chemistry", Chapter 7 36
Solubility Rules:Compounds that Are Generally Soluble in Water
37Tro's "Introductory Chemistry", Chapter 7
Compounds containing the following ions are generally soluble
Exceptions
(when combined with ions on the left the compound is insoluble)
Li+, Na+, K+, NH4+ none
NO3–, C2H3O2
– none
Cl–, Br–, I– Ag+, Hg22+, Pb2+
SO42– Ca2+, Sr2+, Ba2+, Pb2+
Solubility Rules:Compounds that Are Generally Insoluble
38Tro's "Introductory Chemistry", Chapter 7
Compounds containing the following ions are generally insoluble
Exceptions
(when combined with ions on the left the compound is soluble or slightly soluble)
OH– Li+, Na+, K+, NH4+,
Ca2+, Sr2+, Ba2+
S2– Li+, Na+, K+, NH4+,
Ca2+, Sr2+, Ba2+
CO32–, PO4
3– Li+, Na+, K+, NH4+
Determine if Each of the Following Is Soluble in Water KOH AgBr CaCl2 Pb(NO3)2
PbSO4
Tro's "Introductory Chemistry", Chapter 7 39
Determine if Each of the Following Is Soluble in Water, Continued
KOH Soluble, because the cation is K+. AgBr Insoluble, even though most compounds
with Br− are soluble, this is an exception. CaCl2Soluble, most compounds with Cl− are
soluble. Pb(NO3)2 Soluble, because the anion is NO3
−.
PbSO4 Insoluble, even though most compounds with SO4
2− are soluble, this is an exception.
Tro's "Introductory Chemistry", Chapter 7 40
Precipitation Reactions If the ion exchange results
in forming a compound that is insoluble in water, it will come out of solution as a precipitate.
Tro's "Introductory Chemistry", Chapter 7 41
Precipitation Reactions, Continued
42Tro's "Introductory Chemistry", Chapter 7
2 KI(aq) + Pb(NO3)2(aq) 2 KNO3(aq) + PbI2(s)
No Precipitate Formation = No Reaction
43Tro's "Introductory Chemistry", Chapter 7
KI(aq) + NaCl(aq) KCl(aq) + NaI(aq)All ions still present, no reaction.
Process for Predicting the Products ofa Precipitation Reaction1. Write the formula for the reactants and Determine
what ions each aqueous reactant has.2. Exchange ions.
(+) ion from one reactant with (-) ion from the other.3. Balance charges of combined ions to get formula
of each product.4. Balance the equation.
Count atoms.5. Determine solubility of each product in water.
Use the solubility rules. If product is insoluble or slightly soluble, it will
precipitate. If neither product will precipitate, no reaction.
Tro's "Introductory Chemistry", Chapter 7 44
Example 7.7—When an Aqueous Solution of Sodium Carbonate Is Added to an Aqueous Solution of Copper(II) Chloride, a White Solid Forms.
1. Write the formulas of the reactants and Determine the ions present when each reactant dissociates.
Na2CO3(aq) + CuCl2(aq)
2. Exchange the ions.
Tro's "Introductory Chemistry", Chapter 7 45
Practice–Predict the Products and Balance the Equation
KCl(aq) + AgNO3(aq)
Na2S(aq) + CaCl2(aq)
Tro's "Introductory Chemistry", Chapter 7 46
Assignment
Problem Set #3#61, 67, 70
Tro's "Introductory Chemistry", Chapter 7 47
Day Six
Tro's "Introductory Chemistry", Chapter 7 48
Day Seven
Tro's "Introductory Chemistry", Chapter 7 49
Practice—Write an Equation for the Reaction that Takes Place when an Aqueous Solution of ammonium sulfate is Mixed with an Aqueous Solution of lead (II) acetate.
50Tro's "Introductory Chemistry", Chapter 7
Ionic Equations Equations that describe the chemicals put into the water
and the product molecules are called molecular equations.
2 KOH(aq) + Mg(NO3)2(aq) 2 KNO3(aq) + Mg(OH)2(s)
Equations that describe the actual dissolved species are called complete ionic equations. Aqueous electrolytes are written as ions.
○ Soluble salts, strong acids, strong bases.
Insoluble substances and nonelectrolytes written in molecule form.○ Solids, liquids, and gases are not dissolved, therefore, molecule form.
2K+1(aq) + 2OH-1
(aq) + Mg+2(aq) + 2NO3
-1(aq) K+1
(aq) + 2NO3-1
(aq) + Mg(OH)2(s)
Tro's "Introductory Chemistry", Chapter 751
Writing Complete Ionic Equations Rewrite the molecular equation, but
dissociate strong electrolytes into individual ions.
Strong electrolytes must be aqueous.○ Solids, liquids, or gases cannot be electrolytes.
All soluble ionic compounds are strong electrolytes.
Strong acids are strong electrolytes.○ HCl, HNO3, H2SO4..
○ Weak acids are not written in the dissociated ion form. Molecular compounds do not have ions, leave
in the molecular form.
Tro's "Introductory Chemistry", Chapter 7 52
Ionic Equations Ions that are both reactants and products are called
spectator ions.
2K+1(aq) + 2OH-1
(aq) + Mg+2(aq) + 2NO3
-1(aq) K+1
(aq) + 2NO3-1
(aq) + Mg(OH)2(s)
Tro's "Introductory Chemistry", Chapter 7 53
• An ionic equation in which the spectator ions are removed is called a net ionic equation.
2OH-1(aq) + Mg+2
(aq) Mg(OH)2(s)
Writing Net Ionic Equations First, identify the spectator ions in the
complete ionic equation.Identical ions on both sides of the equation.
Cancel out the spectator ions—the result is the net ionic equation.
Tro's "Introductory Chemistry", Chapter 7 54
Summary A molecular equation is a chemical
equation showing the complete, neutral formulas for every compound in a reaction.
A complete ionic equation is a chemical equation showing all of the species as they are actually present in solution.
A net ionic equation is an equation showing only the species that actually participate in the reaction.
Tro's "Introductory Chemistry", Chapter 7 55
Practice–Write the Ionic and Net Ionic Equation.
K2SO4(aq) + Ba(NO3)2(aq) 2 KNO3(aq) + BaSO4(s)
Na2CO3(aq) + 2 HCl(aq) 2 NaCl(aq) + CO2(g) + H2O(l)
Tro's "Introductory Chemistry", Chapter 7 56
Assignment
Problem Set #4 # 73,75, 76
Tro's "Introductory Chemistry", Chapter 7 57
Day Eight
Tro's "Introductory Chemistry", Chapter 7 58
Properties of Acids Sour taste React with “active” metals, not
noble metalsI.e., Al, Zn, Fe, but not Cu, Ag or Au.
Zn + 2 HCl ZnCl2 + H2
Corrosive
React with carbonates, producing CO2.Marble, baking soda, chalk, limestone.
CaCO3 + 2 HCl CaCl2 + CO2 + H2O
React with bases to form ionic saltsAnd often water
Tro's "Introductory Chemistry", Chapter 7 59
Common Acids
Tro's "Introductory Chemistry", Chapter 7 60
Chemical name Formula Old name Strength
Nitric acid HNO3 Aqua fortis Strong
Sulfuric acid H2SO4 Vitriolic acid Strong
Hydrochloric acid HCl Muriatic acid Strong
Phosphoric acid H3PO4 Moderate
Chloric acid HClO3 Moderate
Acetic acid HC2H3O2 Vinegar Weak
Hydrofluoric acid HF Weak
Carbonic acid H2CO3 Soda water Weak
Boric acid H3BO3 Weak
Properties of Bases Taste bitter.
Feel slippery.
React with acids to form ionic salts.And often water.Neutralization.
Tro's "Introductory Chemistry", Chapter 7 61
Common Bases
Tro's "Introductory Chemistry", Chapter 7 62
Chemical name
Formula Common name
Strength
Sodium hydroxide
NaOH Lye, caustic soda
Strong
Potassium hydroxide
KOH Caustic potash Strong
Calcium hydroxide
Ca(OH)2 Slaked lime Strong
Magnesium hydroxide
Mg(OH)2 Milk of magnesia Weak
Ammonium hydroxide
NH4OH, {NH3(aq)}
Ammonia water, aqueous ammonia
Weak
Acid–Base Reactions Also called neutralization reactions because the
acid and base neutralize each other’s properties.
acid + base salt + water2 HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + 2 H2O(l)
The net ionic equation for an acid-base reaction often is:
H+1(aq) + OH-1(aq) H2O(l)As long as the salt that forms is soluble in water.
Tro's "Introductory Chemistry", Chapter 7 63
Process for Predicting the Products ofan Acid–Base Reaction
1. Determine what ions each aqueous reactant has.2. Exchange ions.
(+) ion from one reactant with (-) ion from the other. H+ combines with OH− to make water.
3. Balance charges of combined ions to get formula of the salt.
4. Balance the equation. Count atoms.
5. Determine solubility of the salt. Use the solubility rules. If the salt is insoluble or slightly soluble, it will
precipitate.
Tro's "Introductory Chemistry", Chapter 7 64
Example 7.11—Write the Molecular, Ionic, and Net-Ionic Equation for the Reaction of Aqueous Nitric Acid with Aqueous Calcium Hydroxide.
Tro's "Introductory Chemistry", Chapter 7 65
Practice—Complete and Balance These Acid–Base Reactions.NH4OH(aq) + H2SO4(aq)
Al(OH)3(aq) + H2SO3(aq)
Ba(OH)2(aq) + H2SO4(aq)
Tro's "Introductory Chemistry", Chapter 7 66
Gas Evolution Reactions Reactions in which the driving force is the
production of a material that escapes as a gas are called gas evolution reactions.
Gases that you need to memorize: H2S, NH3, SO2, CO2, NO2, NO, H2, N2, O2, F2, Cl2
Tro's "Introductory Chemistry", Chapter 7 67
Practice—Complete the Following Reactions.
PbS(s) + H2SO4(aq)
Tro's "Introductory Chemistry", Chapter 7 68
Assignment
Problem Set #5#81, 84, 85
Tro's "Introductory Chemistry", Chapter 7 69
Day Nine
Tro's "Introductory Chemistry", Chapter 7 70
Other Patterns in Reactions The precipitation, acid–base, and gas evolving
reactions all involved exchanging the ions in the solution.
Other kinds of reactions involve transferring electrons from one atom to another. These are called oxidation–reduction reactions.Also known as redox reactions.
Tro's "Introductory Chemistry", Chapter 7 71
Oxidation–Reduction Reactions
We say that the element that loses electrons in the reaction is oxidized.
And the substance that gains electrons in the reaction is reduced.
You cannot have one without the other
Tro's "Introductory Chemistry", Chapter 7 72
Summary
Redox reactions occur when:
A substance reacts with O2.
A metal combines with a nonmetal.In general, whenever electrons are
transferred.
Tro's "Introductory Chemistry", Chapter 7 73
Reactions of Metals with Nonmetals (Oxidation–Reduction)
Metals react with nonmetals to form ionic compounds.Ionic compounds are solids at room temperature.
The metal loses electrons and becomes a cation.The metal undergoes oxidation.
The nonmetal gains electrons and becomes an anion.The nonmetal undergoes reduction.
In the reaction, electrons are transferred from the metal to the nonmetal.
2 Na(s) + Cl2(g) NaCl(s)
Tro's "Introductory Chemistry", Chapter 7 74
Recognizing Redox Reactions Any reaction where O2 is a reactant or a product is a redox reaction.
Any reaction between a metal and a nonmetal is redox.
Any reaction where electrons are transferred is redox. When a free element gets combined into a compound, it will
be either oxidized or reduced.
N2(g) + H2(g) NH3(g)When a metal cation changes its charge, it will be either
oxidized if its charge increases or reduced if its charge decreases.
CuCl(aq) + FeCl3(aq) FeCl2(aq) + CuCl2(aq)
Tro's "Introductory Chemistry", Chapter 7 75
Practice—Decide Whether Each of the Following Reactions Is a Redox Reaction.
2 Al(s) + 3 Br2(l) 2 AlBr3(s)
CaSO3(s) + 2 HCl(aq) CaCl2(aq) + SO2(g) + H2O(l)
Fe2O3(s) + C(s) 2 Fe(s) + 3 CO(g)
SO2(g) + O2(g) + H2O(l) H2SO4(aq)
Tro's "Introductory Chemistry", Chapter 7 76
Combustion Reactions Reactions in which O2(g) is
a reactant are called combustion reactions.
Combustion reactions release lots of energy. They are exothermic.
Combustion reactions are a subclass of oxidation–reduction reactions.
Tro's "Introductory Chemistry", Chapter 7 77
2 C8H18(g) + 25 O2(g) 16 CO2(g) + 18 H2O(g)
Products of Combustion When a material burns that contains carbon
and hydrogen, the products are always CO2(g) and H2O(g).
Tro's "Introductory Chemistry", Chapter 7 78
Practice—Write the Equation for Each Reaction.
Combustion of the anesthetic cyclopropane, C3H6.
Combustion of the non-toxic antifreeze propylene glycol, C3H8O2.
Tro's "Introductory Chemistry", Chapter 7 79
Assignment
Problem Set #6 #87-89
Tro's "Introductory Chemistry", Chapter 7 80
Day Ten
Tro's "Introductory Chemistry", Chapter 7 81
Classifying Reactions
One way is based on the process that happens.Precipitation, neutralization, formation of a gas,
or transfer of electrons.
82
Classifying Reactions, Continued Another scheme classifies reactions by
what the atoms do.
83
Type of reaction General equation
Synthesis A + B AB
Decomposition AB A + B
Displacement A + BC AC + B
Double displacement AB + CD AD + CB
Synthesis Reactions Also known as composition or combination
reactions. Two (or more) reactants combine together to
make one product.Simpler substances combining together.
2 CO + O2 2 CO2
2 Mg + O2 2 MgO
HgI2 + 2 KI K2HgI4
Tro's "Introductory Chemistry", Chapter 7 84
Decomposition Reactions
A large molecule is broken apart into smaller molecules or its elements.Caused by addition of energy into the molecule.
Have only one reactant, make 2 or more products.
Tro's "Introductory Chemistry", Chapter 7 85
2h
3
2
223
O 3 O 2
O Hg 2 HgO 2
Cl FeCl 2 FeCl 2
)(
)()()(
g(l)(s)
gls elec
Single Displacement Reactions Reactions that involve one atom
displacing another and replacing it in a compound.
Other examples of displacement reactions are:
Fe2O3(s) + Al(s) Fe(s) + Al2O3(s)
2 Na(s) + 2 H2O(aq) 2 NaOH(aq) + H2(g)
Tro's "Introductory Chemistry", Chapter 7 86
Double Displacement Reactions
Two ionic compounds exchange ions.
X Y (aq) + AB (aq) XB + AY
Precipitation, acid–base, and gas evolving reactions are also double displacement reactions.
Tro's "Introductory Chemistry", Chapter 7 87
Practice—Classify the Following Reactions as Synthesis, Decomposition, Single Displacement, or Double Displacement.
3 Mg(s) + 2 FeCl3(aq) 3 MgCl2(aq) + 2 Fe(s)
CO2(g) + H2O(l) H2CO3(aq)
3 KOH(aq) + H3PO4(aq) K3PO4(aq) + 3 H2O(l)
Tro's "Introductory Chemistry", Chapter 7 88
)(CO )CaO( )(CaCO 23 gss heat
Assignment
Review Sheet
Tro's "Introductory Chemistry", Chapter 7 89