Lecture 9 - sdsuchem200.sdsu.edu … · LECTURE OBJECTIVES • Chapter 4.2-4.4 ... + 10H 2O (g) C...
Transcript of Lecture 9 - sdsuchem200.sdsu.edu … · LECTURE OBJECTIVES • Chapter 4.2-4.4 ... + 10H 2O (g) C...
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CHEM 200/202Professor Gregory P. Holland
Office: GMCS-213C
All emails are to be sent to:[email protected]
My office hours will be held in GMCS-212 on Monday from 12 pm to 2:00 pm or by
appointment.
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ANNOUNCEMENTS
• Chapter 4 problem set is due on 2/14
• First Quiz Thursday 2/13, 10 problems, timed, 60 mins
• First exam 2/15 on Chapters 1-4 (see chem website for sample exams)
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SUPPLEMENTAL INSTRUCTION (SI)
• Study sessions lead by former CHEM 200/202 students that excelled in the previous semesters class.
• Occur ~15 times a week.
• Free to access, no reporting to faculty.
• Students who attend SI regularly score on average ~5% higher than those who do not.
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LECTURE OBJECTIVES• Chapter 4.2-4.4 Classifying Chemical Reactions.
• Define 3 types of chemical reactions (precipitation, acid-base, oxidation-reduction or redox)
• Compute the oxidation states for elements in compounds
• Use oxidation states to identify which compounds are being oxidized and reduced in redox reactions
• Identify limiting reagent in reactions and percent yields
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REDOX REACTION IN COMPOUND FORMATION
Electrons are transferred in the formation of ionic
compounds.
Electrons are shifted in the formation of
covalent compounds.
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OXIDATION NUMBER RULESGeneral Rules1. For an atom in its elemental form (e.g. Na, O2, Cl2,...) the O.N. = 0.2. For a monoatomic ion (e.g. Br-, Cu2+,...) the O.N. = ion charge.3. The sum of the O.N. values for atoms in a compound equals zero. For polyatomic ions the sum equals the charge of the ion.Specific Rules
1. For Group 1(A)1 - O.N. is +1 in all compounds2. For Group 2(A)2 - O.N. is +2 in all compounds3. For hydrogen - O.N. is +1 when bound to nonmetals4. For fluorine - O.N. is -1 when bound to metals & boron5. For oxygen - O.N. is -1 when in peroxides (e.g. H2O2)
- O.N. is -2 for all others (except with fluorine)6. For Group 7(A)17 - O.N. is -1 when with metals, nonmetals
(except O) & for other halogens lower in group
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OXIDATION NUMBERSThe main group elements can
have different oxidation numbers depending on the molecule they are part of.
Compound O.N. of nitrogenNH3 -3N2H4 -2
NH2OH -1N2 0
N2O +1NO +2NO2- +3NO2 +4NO3- +5
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REDOX TERMINOLOGY
• Mg loses electrons
• Mg is oxidized
• Mg is the reducing agent
• The oxidation number of Mg is increased
2Mg(s) + O2(g) → 2MgO(s)
2Mg → 2Mg2+ + 4e- O2 + 4e- → 2O2-
• O gains electrons
• O is reduced
• O is the oxidizing agent
• The oxidation number of O is decreased
O.N.: 0 +2 O.N.: 0 -2
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OXIDATION REDUCTIONOIL RIG
Oxidationisloss of electrons
Reductionisgain of electrons
LEO GER
Loseelectrons isoxidation
Gainelectrons isreduction
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TYPES OF REDOX REACTIONS
• The different types of redox reactions are classified by the components of the reaction and what happens to those components.
• There are four types of redox reactions which involve elements - combination, decomposition, displacement and combustion.
• In these reactions, elements may be reagents, products or transferred during the reaction.
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COMBINATION REACTION2K(s) + Cl2(g) → 2KCl(s)
2NO(g) + O2(g) → 2NO2(g)
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DECOMPOSITION REACTION2HgO(s) → 2Hg(l) + O2(g)
∆ ∆ = heat
2H2O(l)electricity 2H2(g) + O2(g)
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DISPLACEMENT REACTIONAn active metal displacing
hydrogen from water2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)
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DISPLACEMENT REACTIONSDisplacing one metal by another metal
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
More reactive
Less reactive
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COMBUSTION REACTIONS•Combustion reactions always involve oxygen.•The reactions reduce oxygen and release energy, frequently as heat and light.
2CO(g) + O2(g) → 2CO2(g)
2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g)
C6H12O6(g) + 6O2(g) → 6CO2(g) + 6H2O(g)
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REACTION YIELDS• The reaction yield is a measure of the completeness of a
reaction; quantifying how much of the possible product was formed.
• Determining the theoretical yield for a reaction requires a balanced chemical reaction, and the identification of the limiting reagent.
• The limiting reagent is the reagent that will be entirely consumed first, stoping the reaction (limiting the amount of product formed).
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LIMITING REAGENT• The Haber-Bosch process produces ammonia from
nitrogen and hydrogen gas (unbalanced reaction below).
• _N2(g) + _H2(g) → _NH3(g)
• Hydrogen limiting reagent: How many grams of ammonia would be produced if 4.04 g of H2 and an infinite amount of N2? How much N2 is consumed?
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REACTION YIELDS• The reaction yield is a measure of the completeness of a
reaction; quantifying how much of the possible product was formed.
• Determining the theoretical yield for a reaction requires a balanced chemical reaction, and the identification of the limiting reagent.
• The limiting reagent is the reagent that will be entirely consumed first, stoping the reaction (limiting the amount of product formed).
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REACTION YIELDS• Not every reaction proceeds perfectly to produce 100% of the
maximum product.
• Reactions that are imperfect have reaction yields of less than 100%.
• Considering the reaction: _N2(g) + _H2(g) → _NH3(g)
• The reaction was performed with 4.04 g of H2 and excess N2. At the end of the reaction your yield is only 15.0%. What mass of NH3 is formed?
• If the reaction produced 7.24 g NH3. What would the yield be?
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LIMITING REAGENT PROBLEM
• What is the limiting reagent when 2.00 g of Si and 1.50 g of N2 is reacted? How many moles of Si3N4 will be produced? Be sure to balance the equation first.
_Si(s) + _N2(g) → _Si3N4(s)