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Chemical ReactionsChemical ReactionsChapter 11Chapter 11
General Chemistry
ObjectivesObjectives• Balance chemical equations by applying Balance chemical equations by applying
the law of conservation of mass. the law of conservation of mass. • Recognize synthesis, decomposition, Recognize synthesis, decomposition,
single displacement, double single displacement, double displacement, and neutralization displacement, and neutralization reactions.reactions.
• Write chemical equations from words.Write chemical equations from words.• Predict the products of chemical Predict the products of chemical
reactions.reactions.• Write net ionic equations for reactions.Write net ionic equations for reactions.
Chemical Reactions Chemical Reactions BasicsBasics
Chemical ReactionsChemical Reactions
A A chemical reactions chemical reactions are chemical are chemical changes.changes.
Recall: chemical changes are when Recall: chemical changes are when one or more substances are changed one or more substances are changed into different substancesinto different substances• Examples: wood burning, metal rustingExamples: wood burning, metal rusting
Indications of a Chemical ReactionIndications of a Chemical Reaction Certain easily observed changes indicate Certain easily observed changes indicate
that a chemical reaction has occurred:that a chemical reaction has occurred: evolution of energy by heat and/or lightevolution of energy by heat and/or lightcolor changecolor changeproduction of gasproduction of gasproduction of precipitateproduction of precipitate
A solid that is produced as a result of a chemical A solid that is produced as a result of a chemical reaction in solution and that separates from the reaction in solution and that separates from the solution is known as asolution is known as a precipitateprecipitate
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Law of Conservation of MatterLaw of Conservation of Matter Chemical reactions obey the Law of Chemical reactions obey the Law of
Conservation of MatterConservation of Matter
in all chemical and physical changes, in all chemical and physical changes, matter is neither created or destroyedmatter is neither created or destroyed
The total mass in a chemical reaction The total mass in a chemical reaction remains constantremains constant
Chemical EquationsChemical Equations A A chemical equation chemical equation represents, with symbols and represents, with symbols and
formulas, the identities and the amounts of the formulas, the identities and the amounts of the reactants and products in a chemical reaction.reactants and products in a chemical reaction.
Has two parts: Has two parts: • Reactants:Reactants: the substances you start with the substances you start with• Products:Products: the substances you end up with the substances you end up with
The reactants turn into the productsThe reactants turn into the products
4 Fe + 3 O4 Fe + 3 O22 2 Fe 2 Fe22OO33
Reactants Reactants products products
Ways to Express a Chemical Ways to Express a Chemical ReactionReaction
The way atoms are joined is changed in a The way atoms are joined is changed in a chemical reaction.chemical reaction.Can be described several ways:Can be described several ways:
1. In a 1. In a sentence sentence Copper reacts with chlorine to form copper (II) Copper reacts with chlorine to form copper (II)
chloride.chloride.
2. In a 2. In a word equationword equationCopper + chlorine Copper + chlorine copper (II) chloride copper (II) chloride
3. In 3. In formula equationformula equation::Cu + ClCu + Cl22 CuCl CuCl22
Symbols Used in Chemical Symbols Used in Chemical EquationsEquations
Additional Symbols Used in Additional Symbols Used in EquationsEquations
shows that shows that heat heat is supplied to the is supplied to the reactionreaction
is used to indicate a is used to indicate a catalystcatalyst is supplied, in this case, is supplied, in this case, platinum.platinum.
heat ,
Pt
What is a catalyst?What is a catalyst?
A A catalystcatalyst is a substance that is a substance that speeds up a reaction, without speeds up a reaction, without being changed or used up by the being changed or used up by the reaction.reaction.Enzymes are biological or protein Enzymes are biological or protein
catalysts.catalysts.
Study Buddy ReviewStudy Buddy Review
What are four things that indicate a What are four things that indicate a chemical reaction has taken place?chemical reaction has taken place?
What is the Law of Conservation of What is the Law of Conservation of mass?mass?
What does the symbol (l) mean?What does the symbol (l) mean? What does (aq) mean?What does (aq) mean?
Balancing Chemical Balancing Chemical EquationsEquations
Skeleton and Balanced Skeleton and Balanced EquationsEquations
Skeleton equations: Skeleton equations: do not do not indicate how many of each indicate how many of each element/compound element/compound
Balanced equations:Balanced equations: the number the number of atoms of each element is the of atoms of each element is the same on both sides of the same on both sides of the reaction.reaction.
Numbers in Balanced EquationsNumbers in Balanced Equations
Use coefficients to balance equationUse coefficients to balance equation
Coefficients:Coefficients: large whole numbers placed large whole numbers placed in front of formula which represents in front of formula which represents number of units of that compoundnumber of units of that compound
Subscript:Subscript: small whole number placed in small whole number placed in chemical formula to represent number of chemical formula to represent number of atoms of an element in a compoundatoms of an element in a compound
4 Fe + 3 O4 Fe + 3 O22 2 Fe 2 Fe22OO33
Coefficient subscript
Balanced EquationBalanced Equation
A A balanced equation balanced equation has the has the same number of atoms of each same number of atoms of each element on both sides of the element on both sides of the equationequation
Atoms can’t be created or Atoms can’t be created or destroyeddestroyed
All the atoms at the beginning All the atoms at the beginning must appear in the endmust appear in the end
C + OC + O22 CO CO We need one more oxygen in the We need one more oxygen in the
products.products. Can’t change the formula, because it Can’t change the formula, because it
describes what it is (carbon monoxide in describes what it is (carbon monoxide in this example)this example)
C + O COO
Must be used to make another COMust be used to make another CO But where did the other C come from?But where did the other C come from?
C +O
C
OO
OC
Must have started with two CMust have started with two C 2 C + O2 C + O22 2 CO 2 CO
C
+O
C
OO
OC
C
Rules for balancing:Rules for balancing:
Assemble, write the Assemble, write the correct formulascorrect formulas for for all the reactants and productsall the reactants and products
Count the number of atoms of each type Count the number of atoms of each type of element appearing on both sidesof element appearing on both sides
Balance the atoms of an element one at a Balance the atoms of an element one at a time by adding coefficients (the numbers time by adding coefficients (the numbers in front) - save H and O until LAST!in front) - save H and O until LAST!
Check to make sure it is balanced.Check to make sure it is balanced.
Never change a subscript to balance an Never change a subscript to balance an equation.equation.• If you change the formula you are If you change the formula you are
describing a different reaction.describing a different reaction.
• HH22O is a different compound than HO is a different compound than H22OO22
Never put a coefficient in the middle of Never put a coefficient in the middle of a formulaa formula• 2 NaCl is okay, Na2Cl is not.2 NaCl is okay, Na2Cl is not.
Balancing Equations ExamplesBalancing Equations Examples
HH22 (g) (g) + O+ O22 (g) (g) H H22O (l)O (l)
Zn + HCl Zn + HCl H H22 + ZnCl + ZnCl22
Pb (NOPb (NO33))22 + K + K22S S PbS + KNO PbS + KNO33
Balancing Equations Balancing Equations AnswersAnswers
22 H H22 (g) (g) + O+ O22 (g) (g) 22 H H22O (l)O (l)
Zn + Zn + 22 HCl HCl H H22 + ZnCl + ZnCl22
Pb (NOPb (NO33))22 + K + K22S S 22PbS + PbS + 22KNOKNO33
Word Equation ExamplesWord Equation Examples
Write a balanced chemical equation Write a balanced chemical equation for the following:for the following:
Aqueous solutions of sulfuric acid Aqueous solutions of sulfuric acid and sodium hydroxide react to form and sodium hydroxide react to form aqueous sodium sulfate and water.aqueous sodium sulfate and water.
Five General Types of Five General Types of Chemical ReactionsChemical Reactions
Five General Types of Five General Types of Chemical ReactionsChemical Reactions
1.1. Synthesis (Composition)Synthesis (Composition)
2.2. DecompositionDecomposition
3.3. Single-ReplacementSingle-Replacement
4.4. Double-ReplacementDouble-Replacement
5.5. CombustionCombustion
By knowing the type of reaction that is By knowing the type of reaction that is occurring, you can predict the products occurring, you can predict the products that will be formed.that will be formed.
General Types of Chemical General Types of Chemical ReactionsReactions
Combination: Combination: A + B A + B AB AB Decomposition: Decomposition: AB AB A + B A + B Single Replacement :Single Replacement :
AX +B AX +B A + BX A + BX Double Replacement: Double Replacement:
AX + BY AX + BY AY + BX AY + BX Combustion:Combustion:
CCxxHHyy + O+ O22 CO CO22 + H + H22OO
Synthesis (Combination)
General form: A + B AB (two reactants make a single product)
A, B = elements or compoundsAB = compound consisting of A and B
This is the only type of chemical reaction in which there is a single product formed. This single product is
always more complex than the reactants.
Examples of Synthesis Reactions
a. calcium + oxygen yields calcium oxide 2Ca + O2 2CaO
b. carbon dioxide + water yields carbonic acidCO2 + H2O H2CO3
Notice: All equations show two (or more) reactants, but only one product.
http://www.ric.edu/ptiskus/reactions/Index.htm
Decomposition ReactionsDecomposition Reactions
(Decomposing = breaking down into (Decomposing = breaking down into smaller parts; microorganisms)smaller parts; microorganisms)
A reaction in which a single compound is A reaction in which a single compound is broken into 2 or more smaller compounds broken into 2 or more smaller compounds or elements. The opposite of direct or elements. The opposite of direct combination/synthesis.combination/synthesis.
You can identify this reaction because there You can identify this reaction because there is only one reactant.is only one reactant.
General form: General form: AB AB A + B A + B AB = compoundAB = compound
A, B = elements or simpler compoundsA, B = elements or simpler compounds
Examples of Decomposition Examples of Decomposition ReactionsReactions
Water yields hydrogen and oxygenWater yields hydrogen and oxygen
2H2H22O O 2H 2H2 2 + O + O22
marble (rock) yields (with heating) marble (rock) yields (with heating) calcium oxide and carbon dioxidecalcium oxide and carbon dioxide
CaCOCaCO3 3 CaO + CO CaO + CO22
Notice: single compound decomposes Notice: single compound decomposes into two (or more) products.into two (or more) products. http://www.ric.edu/ptiskus/reactions/Index.htm
Single-Replacement ReactionsSingle-Replacement Reactions
One element and one compound One element and one compound recombine (switch partners)recombine (switch partners)
General Form: A + BX General Form: A + BX AX + B AX + B
AX, BX = ionic compoundsAX, BX = ionic compounds
A, B = elementsA, B = elements
X = ion that switches partnersX = ion that switches partners
Examples of Single-Replacement Examples of Single-Replacement ReactionsReactions
Magnesium metal and copper (II) Magnesium metal and copper (II) sulfatesulfate
Mg + CuSOMg + CuSO4 4 MgSO MgSO44 + Cu + Cu
Iron metal and copper (II) sulfate)Iron metal and copper (II) sulfate)
Fe + CuSOFe + CuSO44 FeSO FeSO44 + Cu + Cu
www.ric.edu/ptiskus/reactions/Index.htm
Double-Replacement ReactionsDouble-Replacement Reactions
Positive ions in two compounds are Positive ions in two compounds are exchanged.exchanged.
Look for: 2 compounds as reactants and Look for: 2 compounds as reactants and 2 compounds as products.2 compounds as products.
Reactants are usually ionic compounds.Reactants are usually ionic compounds. Specific example: neutralization Specific example: neutralization
reactions between acid and basereactions between acid and base
General form: AX + BY General form: AX + BY AY + BX AY + BX
(Notice: X and Y “change partners”)(Notice: X and Y “change partners”)
Examples of Double Replacement Examples of Double Replacement ReactionsReactions
Calcium carbonate and hydrochloric Calcium carbonate and hydrochloric acid yield calcium chloride and acid yield calcium chloride and carbonic acid.carbonic acid.
CaCOCaCO33 + 2HCl + 2HCl CaCl CaCl22 + H + H22COCO33
www.ric.edu/ptiskus/reactions/Index.htm
Rules of Double-Displacement Rules of Double-Displacement ReactionsReactions
Reactants must be dissolved in Reactants must be dissolved in water (releasing the ions).water (releasing the ions).
Will occur ifWill occur if::1.1. One of the products is a molecule One of the products is a molecule
(covalent), (covalent),
2.2. A precipitate (solid comes out of A precipitate (solid comes out of solution), orsolution), or
3.3. An insoluble gas.An insoluble gas.
Combustion ReactionsCombustion Reactions
Reactants: Reactants: a fuel (usually a hydrocarbon) a fuel (usually a hydrocarbon) and oxygen.and oxygen.
Products: Products: water, carbon dioxide, and lots water, carbon dioxide, and lots of energy! (heat, light)of energy! (heat, light)
Examples: Examples: CHCH44 (methane) + 2O (methane) + 2O2 2 2H 2H22O + COO + CO22
CC22HH55OH (gasohol) + 3OOH (gasohol) + 3O22 3H 3H22O + 2COO + 2CO22
www.ric.edu/ptiskus/reactions/Index.htm
Study Buddy ReviewStudy Buddy Review
Describe each of the following to your Describe each of the following to your study buddy:study buddy:
• Synthesis (combination)Synthesis (combination)• DecompositionDecomposition• Single-ReplacementSingle-Replacement• Double-ReplacementDouble-Replacement• CombustionCombustion
Activity SeriesActivity Series
Activity Series and Single Activity Series and Single Replacement ReactionsReplacement Reactions
AlAl ++ CuClCuCl22 ??? ???
Cu +Cu + AlClAlCl33 ??? ???
Only one of the following reactions Only one of the following reactions will occurwill occur
How do you know which one? How do you know which one?
Activity Series of MetalsActivity Series of Metals
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Activity Series RulesActivity Series Rules
Elements at top of series are most Elements at top of series are most activeactive
Elements at bottom of series are least Elements at bottom of series are least active (coinage metals)active (coinage metals)
Elements at the top of the series will Elements at the top of the series will replace elements replace elements below it below it in a chemical in a chemical reaction.reaction.
Example: Al + CuClExample: Al + CuCl22 will occur will occur
Cu + AlClCu + AlCl33 will NOT occur will NOT occur
Activity Series ExamplesActivity Series Examples
Using the activity series, predict Using the activity series, predict whether each of the possible whether each of the possible reactions will occur:reactions will occur:• Cr + HCr + H22O O
• Pt + OPt + O22
• Cd + 2HBr Cd + 2HBr
Activity Series ExamplesActivity Series Examples
Using the activity series, predict Using the activity series, predict whether each of the possible whether each of the possible reactions will occur:reactions will occur:• Cr + HCr + H22O O NRNR
• Pt + OPt + O22 NRNR
• Cd + 2HBr Cd + 2HBr CdBrCdBr22 + H + H22
ReferencesReferences
Dr. Stephen L. Cotton Charles Dr. Stephen L. Cotton Charles Page High SchoolPage High School
Mrs. LijekMrs. Lijek