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Chemistry I Honors—Unit 6: Chemical Equations / Reactions/ Redox. Objectives #1-2: Introduction to Chemical Reactions, Reaction Interpretation, and Balancing. Chemical Equations Describe chemical reactions Starting substances are called reactants Ending substances are called products
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Chemistry I Honors—Unit 6: Chemical Equations / Reactions/Redox
Objectives #1-2:Introduction to Chemical Reactions, Reaction Interpretation, and Balancing • Chemical Equations • Describe chemical reactions • Starting substances are called reactants • Ending substances are called products • All chemical reactions must follow the Law of Conservation of Matter by being balanced
II. Interpreting Chemical Equations A. Symbols
Objectives #1-2:Introduction to Chemical Reactions, Reaction Interpretation, and Balancing II. B. Writing Unbalanced Equations --See examples in packet III. Balancing Chemical Equations • Basic Procedures: • Be sure all formulasare correct before attempting to balance • Never balance by changing subscripts • Use coefficientsto balance • Typeand number of atoms on each side of reaction must balance • Coefficients used must be in the lowest • ratio possible
Objectives #1-2:Introduction to Chemical Reactions, Reaction Interpretation, and Balancing (examples in lecture guide)
Objective #3: Assignment of Oxidation Numbers Part I: Oxidation vs. Reduction • Oxidation is the loss of electrons; during this process the charge of a species increases • Reduction is the gain of electrons; during this process the charge of a species decreases • “OIL RIG” (oxidation is loss, reduction is gain)
Objective #3: Assignment of Oxidation Numbers (video clip) • Example I: Solid magnesium is reacted with oxygen gas in the air to produce solid magnesium oxide • Equation: 0 0 +2 -2 • Mg(s) + O2 (g) MgO(s) *What is the magnesium doing? Mg --› Mg+2 + 2e-1 *What is the oxygen doing? O + 2e-1 --› O-2
*Which element has been oxidized? Mg *Which element has been reduced? O
Objective #3: Assignment of Oxidation Numbers *Example II: Water is added to produce sufficient heat to react solid forms of aluminum and iodine. The resulting reaction produces solid aluminum iodide. • Equation: 0 0 +3 -1 Al(s) + I2(s) --› AlI3 (s) *What is the aluminum doing? Al --› Al+3 + 3e-1 *What is the iodine doing? I + e-1 --› I-1
*Which element has been oxidized? Al *Which element has been reduced? I
Objective #3 Assignment of Oxidation Numbers • In general, during REDOX reactions, • Metals tend to lose electrons and are oxidized • Nonmetalstend to gain electrons and are reduced
Objective #3: Assignment of Oxidation Numbers Part II: Utilization of Oxidation Number Rules • See text p.232-233 • The “Big 4”: Group I elements are +1 Group II elements are +2 H is usually +1 O is usually -2 • Examples (see packet) • Demo Redox Reaction
Objective #4 Balancing Redox Reactions *Writing Half-Reactions (charges and atoms must balance) (examples)
Objective #4: Balancing Redox Reactions • Key Steps: 1.Write half-reactionsfor the oxidation and reduction sections of the reaction. 2. Balance all elements except hydrogenand oxygen. 3. Balance oxygen by using water. 4. Balance hydrogen by using hydrogen ions.
Objective #4: Balancing Redox Reactions 5.Balance charge by adding electrons to the side that is deficientin electrons. 6. Equalize electrons lost and gained by multiplyingeach half-reaction by an appropriate factor. 7.Addtogether half-reactions and cancellike species. 8.Check that atoms and chargesbalance. (examples)
Objective #5: Oxidizing and Reducing Agents • Examples—see packet
Objective #5: Oxidizing and Reducing Agents • Summary: • The charge of the element oxidized goes up • The charge of the element reduced goes down • The item oxidized is the reducingagent • The item reduced is the oxidizingagent
Objective #6 Oxidation-Reduction Reactions *recall that oxidation-reduction reactions involve the transfer of electrons A. Synthesis Reactions *general formula: A + B --›AB *examples:
B. Decomposition Reactions *general formula: AB --› A + B *examples:
C. Single-Displacement Reactions *general formula: A + BC --› AC + B *examples:
D. Combustion Reactions *examples: Element + oxygen -- oxide Hydrocarbon + oxygen -- water and carbon dioxide
Objective #8 Activity Series *an activity series is a vertical listing of elements in terms of their chemical reactivity; elements that are more reactive are listed at the top and less reactive elements are listed near the bottom *a reactive element can readily transfer its valence electrons to another element *in general, for a single replacement reaction to go to completion, the lone element in the reaction must be higher on activity series that the element in the compound it is trying to displace
*it should be remembered however that an activity series should only be used as a general guide for predicting singlereplacement reactions (see Table 3 on p.286) *predict if the following reactions will occur: Zn + H2O --› (assume Zn is +2 if rx. occurs) No Rx. Sn + O2 --› (assume Sn is +4 if rx. occurs) Rx. Occurs SnO2
Cd + Pb(NO3)2 --› (assume Cd has a +2 charge if rx. Occurs) Rx. occurs Cd(NO3)2 + Pb Cu + HCl --› (assume Cu has a charge of +2 if rx. Occurs) No Rx.
Objective #7 Double Replacement Reactions *general formula: AB + CD --› AD + CB *Type I Formation of a Precipitate (precipitation) Ionic compound + ionic compound --› aqueous solution + precipitate Pb(NO3)2 + NaI --› NaNO3 + PbI2(s) Na2S + Pb(NO3)2 --› PbS(s) + NaNO3
*Type II Formation of a Gas Ionic compound + ionic compound --› gas + aqueous solution + water NH4Cl + NaOH --› NH4OH + NaCl ^ NH3 + H2O Na2SO3 + HCl --› H2SO3 + NaCl ^ SO2 + H2O
*Type III Formation of Water (acid-base) Acid + Base --› water + salt NaOH + HCl --› H2O + NaCl Ca(OH)2 + HCl --› H2O + CaCl2
Practice in Predicting the Products of Chemical Reactions (see example in lecture guide)
Objectives #9: Compounds in Aqueous Solutions Part I Dissociation of Ionic Compounds *dissociation process: The separation of ions that occurs when an ionic compound is dissolved in water. *examples: CaCl2(aq) --› Ca+2(aq) + 2Cl-1(aq) Al(NO3)3(aq) --› Al+3(aq) + 3NO3-1(aq)
Part II Predicting Precipitation *use of the solubility table in lecture guide *examples:
Objectives #9: Compounds in Aqueous Solutions Part III Writing Net Ionic Equations *net reaction vs. spectator ions (examples)