1 Announcements & Agenda (02/02/07) Will post these later today Pick up quizzes (Ave = 7.1/10) Exam @ 11 am this Friday Review Wed @ 5 pm, Room TBA Review.

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AnnouncementsAnnouncements & Agenda& Agenda (02/02/07)(02/02/07)Will post these later today Will post these later today Pick up quizzes (Ave = 7.1/10)Pick up quizzes (Ave = 7.1/10)Exam @ 11 am this FridayExam @ 11 am this Friday Review Wed @ 5 pm, Room TBAReview Wed @ 5 pm, Room TBA Covers Ch 1-5 +Intermolecular Forces (Notes) + LabCovers Ch 1-5 +Intermolecular Forces (Notes) + Lab WILL NOT include Ch 7 except the notes from todayWILL NOT include Ch 7 except the notes from today

TodayToday Redox Rxns (5.3, 5.4)Redox Rxns (5.3, 5.4) Energy of Chemical Reactions (5.9)Energy of Chemical Reactions (5.9) Intermolecular Forces (Notes: Will be on Exam)Intermolecular Forces (Notes: Will be on Exam)

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Last Time: Mass is Conserved in Chemical Last Time: Mass is Conserved in Chemical Reactions but Need Mole to Solve ProblemsReactions but Need Mole to Solve Problems

2 moles Ag + 1 moles S = 1 mole Ag2 moles Ag + 1 moles S = 1 mole Ag22SS

2 (107.9 g) + 1(32.1 g) = 1 (247.9 g) 2 (107.9 g) + 1(32.1 g) = 1 (247.9 g) 247.9 247.9 g reactants = 247.9 g productg reactants = 247.9 g product

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Take home message: Why the mole is Take home message: Why the mole is so important in chemistry.so important in chemistry.

The molecular picture of matter

• It is just a number (a quantity) of atoms or molecules that allows to think about reactions s that allows to think about reactions on a macroscopic scaleon a macroscopic scale

• When trying to determine how much “stuff” is needed or en trying to determine how much “stuff” is needed or produced in a chemical reaction, we find that tproduced in a chemical reaction, we find that the balanced equation

works in “moles” doesn’t work in mass

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Last Time: Several Types of Reactions (5.3)Last Time: Several Types of Reactions (5.3)

Chemical reactions can be classified as: Chemical reactions can be classified as:

• combination reactions.combination reactions.

• decomposition reactions.decomposition reactions.

• single replacement reactions.single replacement reactions.

• double replacement reactions.double replacement reactions.

Don’t stress about these too much; be able to Don’t stress about these too much; be able to recognize the different flavors (see suggested recognize the different flavors (see suggested problems)problems)

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Oxidation-Reduction Reactions (5.4)Oxidation-Reduction Reactions (5.4)

An oxidation-reduction reaction An oxidation-reduction reaction

• provides us with energy from food.provides us with energy from food.• provides electrical energy in provides electrical energy in

batteries.batteries.• occurs when iron rusts.occurs when iron rusts.

4Fe(4Fe(ss) + 3O) + 3O22((gg) ) 2Fe 2Fe22OO33((ss))

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An oxidation-reduction reactionAn oxidation-reduction reaction

• transfers electrons from one reactant to another.transfers electrons from one reactant to another.

• loses electrons in oxidation. (LEO) loses electrons in oxidation. (LEO)

Zn(Zn(ss)) Zn Zn2+2+((aqaq)) + 2e+ 2e- - (loss of e(loss of e--))

• gains electrons in reduction. (GER)gains electrons in reduction. (GER)CuCu2+2+((aqaq) + 2e) + 2e- - Cu( Cu(ss) (gain of e) (gain of e--))

Electron Loss and GainElectron Loss and Gain

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Oxidation and ReductionOxidation and Reduction

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Write the separate oxidation and reduction reactions Write the separate oxidation and reduction reactions for the following equation.for the following equation.

2Cs(2Cs(ss) + F) + F22((gg) ) 2CsF( 2CsF(ss))

A cesium atom loses an electron to form cesium ion.A cesium atom loses an electron to form cesium ion.

Cs(Cs(ss) ) CsCs++((ss) + 1e) + 1e− − oxidationoxidation

Fluorine atoms gain electrons to form fluoride ions.Fluorine atoms gain electrons to form fluoride ions.

FF22((ss) + 2e) + 2e-- 2F 2F−−((ss) ) reductionreduction

Writing Oxidation & Reduction ReactionsWriting Oxidation & Reduction Reactions

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Cu and AgCu and Ag1+1+

Cu(s) Cu2+(aq) + 2e- oxidationOrange metal Blue

Ag1+(aq) + 2e- Ag(s) reduction Colorless Silver

COOL DEMO!COOL DEMO!

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Collision Theory of Reactions (5.9)Collision Theory of Reactions (5.9)

A chemical reaction occurs whenA chemical reaction occurs when

• collisions between molecules have sufficient collisions between molecules have sufficient energy to break the bonds in the reactants. energy to break the bonds in the reactants.

• bonds between atoms of the reactants (Nbonds between atoms of the reactants (N22 and and

OO22) are broken and new bonds (NO) can form. ) are broken and new bonds (NO) can form.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Activation EnergyActivation Energy

• The activation The activation energy is the energy is the minimum energy minimum energy needed for a needed for a reaction to take reaction to take place.place.

• When a collision When a collision provides energy provides energy equal to or equal to or greater than the greater than the activation energy, activation energy, product can form.product can form.

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• heat is released.heat is released.• the energy of the products the energy of the products

is less than the energy of is less than the energy of the reactants.the reactants.

• heat is a product.heat is a product.

C(s) + 2 H2(g) CH4(g) + 18 kcal

Exothermic ReactionsExothermic Reactions

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Endothermic ReactionsEndothermic Reactions

• Heat is absorbed.Heat is absorbed.• The energy of the The energy of the

products is greater than products is greater than the energy of the the energy of the reactants.reactants.

• Heat is a reactant (added).Heat is a reactant (added).

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

N2(g) + O2 (g) + 43.3 kcal 2NO(g)

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SummarySummary

Reaction Reaction Energy Energy Heat Heat TypeType ChangeChange in Reactionin Reaction

Endothermic Heat absorbed Endothermic Heat absorbed ReactantReactant

Exothermic Heat released Exothermic Heat released ProductProduct

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Rate of ReactionRate of Reaction

• is the speed at which reactant is used up.is the speed at which reactant is used up.

• is the speed at which product forms.is the speed at which product forms.

• increases when temperature rises because increases when temperature rises because reacting molecules move faster providing reacting molecules move faster providing more colliding molecules with energy of more colliding molecules with energy of activation.activation.

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Reaction Rate and CatalystsReaction Rate and Catalysts

A A catalystcatalyst • increases the increases the

rate of a reaction.rate of a reaction.• lowers the lowers the

energy of energy of activation. activation.

• is not used up is not used up during the during the reaction.reaction.

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Learning CheckLearning Check

State the effect of each on the rate of reaction as:State the effect of each on the rate of reaction as:

1) increases 2) decreases1) increases 2) decreases 3) no change 3) no change

A. increasing the temperature.A. increasing the temperature.

B. removing some of the reactants.B. removing some of the reactants.

C. adding a catalyst.C. adding a catalyst.

D. placing the reaction flask in ice.D. placing the reaction flask in ice.

E. increasing the concentration of one of the reactants.E. increasing the concentration of one of the reactants.

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Intermolecular Forces (Notes Only)Intermolecular Forces (Notes Only)

Inter-Inter- vs.vs. Intra-Intra-

Latin:Latin: Between Between AmongAmong moleculesmolecules moleculesmolecules

Dispersion ForcesDispersion ForcesDipolar ForcesDipolar ForcesHydrogen BondingHydrogen Bonding

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Phases of elements at STPPhases of elements at STP

Only 11 elements are gasesOnly 11 elements are gasesWhy? Why? Intermolecular forcesIntermolecular forces: forces of attraction : forces of attraction between molecules which result in liquids and between molecules which result in liquids and solidssolids

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On what do the intermolecular forces depend?

Molar mass

Polarity

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Melting & Boiling PointsMelting & Boiling Points

Both are indicators of the strengths of Both are indicators of the strengths of intermolecular forces:intermolecular forces:

freezing pointfreezing point (fp): the temperature at which a solid & (fp): the temperature at which a solid & liquid coexist at equilibrium under ‘normal’ pressuresliquid coexist at equilibrium under ‘normal’ pressures

boiling pointboiling point (bp): the temperature at which a liquid & (bp): the temperature at which a liquid &

vapor coexist at equilibrium under ‘normal’ pressuresvapor coexist at equilibrium under ‘normal’ pressures

Exam Questions: Rank Compounds by BPs OR Exam Questions: Rank Compounds by BPs OR Explain why one compound has a higher bp/mp than Explain why one compound has a higher bp/mp than another bases on IM forcesanother bases on IM forces

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Intermolecular forces: Intermolecular forces: Actually all the same force!Actually all the same force!

ElectrostaticElectrostatic

Dispersion Forces: Dispersion Forces: From polarizability of atomsFrom polarizability of atoms

Dipolar Forces: Dipolar Forces: From permanent dipole momentsFrom permanent dipole moments

Hydrogen-bonding:Hydrogen-bonding: Special case of dipolar forcesSpecial case of dipolar forces

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… … but remember that intermolecular but remember that intermolecular forces are weaker than covalent or forces are weaker than covalent or

ionic bonds!!!!ionic bonds!!!!

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1. Dispersion Forces1. Dispersion ForcesFound in all molecular substancesFound in all molecular substancesElectrostatic in nature; arise from attractions involving Electrostatic in nature; arise from attractions involving induced dipoles.induced dipoles.

Magnitude depends on how easy it is to Magnitude depends on how easy it is to polarizepolarize the the electron cloud of a molecule.electron cloud of a molecule.

larger molecules have larger larger molecules have larger polarizabilitypolarizability..

Ask me about Ask me about Geckos?Geckos?

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Polarizability increases…. with increasing MM

p. 92

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1. Dispersion Forces:1. Dispersion Forces: Larger shapes are more polarizable

Higher boiling point

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Intermolecular ForcesIntermolecular Forces

Intermolecular forces not only hold small molecules in liquids and solids together, but also drive very large molecules to bind to each other - this is necessary for cell functions.

(Turn on a gene)

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Individually, dispersion (van der Waal’s) forces are thought of as very weak. However, these forces between large molecules can be very strong - e.g. motor oil, vaseline are entirely non-polar molecules.

In water “hydrophobic bonding” drives large non-polar molecules or parts of molecules together.

Sodium dodecyl sulfate (= sodium lauryl sulfate)

CH3-CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2-SO3-

Nonpolar Hydrophobic = “water-hating” Ionic

Hydrophillic = “water loving”

1. More on London Dispersion Forces1. More on London Dispersion Forces

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2.2. Dipolar ForcesDipolar Forces

Occur when one polar molecule encounters Occur when one polar molecule encounters another polar molecule.another polar molecule.The positive ends will be attracted to the The positive ends will be attracted to the negative ends.negative ends.Dipolar forces are typically stronger than Dipolar forces are typically stronger than dispersion forces.dispersion forces.Dipolar forces increase with an increase in the Dipolar forces increase with an increase in the polarity of the molecule.polarity of the molecule.NOTE: Ion-dipole forces stronger than dipolar NOTE: Ion-dipole forces stronger than dipolar forces.forces.

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2. Dipolar Forces:2. Dipolar Forces: permanent dipole monents….

Higher boiling point

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ExampleExampleExplain the trend in bp’s: butane (0°C), methyl ethyl Explain the trend in bp’s: butane (0°C), methyl ethyl ether (8°C) and acetone (56°C).ether (8°C) and acetone (56°C).

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• Special case of dipole-dipole forces.• By experiments: boiling points of compounds with

H-F, H-O, and H-N bonds are abnormally high.• Intermolecular forces are abnormally strong.

3. Hydrogen Bonding3. Hydrogen Bonding

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Hydrogen Bonding

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Hydrogen Bonding

Hydrogen BondingHydrogen Bonding

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-

+

Electron deficient H atom

Electronegative atom with lone pair

p. 94