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

2 Last Time: Mass is Conserved in Chemical Reactions but Need Mole to Solve Problems 2 moles Ag + 1 moles S = 1 mole Ag 2 S 2 (107.9 g) + 1(32.1 g) = 1 (247.9 g) g reactants = g product

3 Take home message: Why the mole is so important in chemistry.  The molecular picture of matter s that allows to think about reactions on a macroscopic scaleIt is just a number (a quantity) of atoms or molecules that allows to think about reactions on a macroscopic scale en trying to determine how much “stuff” is needed or produced in a chemical reaction, we find that tWhen trying to determine how much “stuff” is needed or produced in a chemical reaction, we find that the balanced equation  works in “moles”  doesn’t work in mass

4 Last Time: Several Types of Reactions (5.3) 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 recognize the different flavors (see suggested problems)

5 Oxidation-Reduction Reactions (5.4) An oxidation-reduction reaction provides us with energy from food.provides us with energy from food. provides electrical energy in batteries.provides electrical energy in batteries. occurs when iron rusts.occurs when iron rusts. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s)

6 An 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(s) Zn 2+ (aq) + 2e - (loss of e - ) gains electrons in reduction. (GER)gains electrons in reduction. (GER) Cu 2+ (aq) + 2e - Cu(s) (gain of e - ) Electron Loss and Gain

7 Oxidation and Reduction

8 Write the separate oxidation and reduction reactions for the following equation. 2Cs(s) + F 2 (g) 2CsF(s) A cesium atom loses an electron to form cesium ion. A cesium atom loses an electron to form cesium ion. Cs(s) Cs + (s) + 1e − oxidation Fluorine atoms gain electrons to form fluoride ions. F 2 (s) + 2e - 2F − (s) reduction Writing Oxidation & Reduction Reactions

9 Cu and Ag 1+ Cu(s) Cu 2+ (aq) + 2e- oxidation Orange metal Blue Ag 1+ (aq) + 2e- Ag(s) reduction Colorless Silver COOL DEMO!

10 Collision Theory of Reactions (5.9) A chemical reaction occurs when collisions between molecules have sufficient energy to break the bonds in the reactants.collisions between molecules have sufficient energy to break the bonds in the reactants. bonds between atoms of the reactants (N 2 and O 2 ) are broken and new bonds (NO) can form.bonds between atoms of the reactants (N 2 and O 2 ) are broken and new bonds (NO) can form. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

11 Activation Energy The activation energy is the minimum energy needed for a reaction to take place.The activation energy is the minimum energy needed for a reaction to take place. When a collision provides energy equal to or greater than the activation energy, product can form.When a collision provides energy equal to or greater than the activation energy, product can form.

12 heat is released.heat is released. the energy of the products is less than the energy of the reactants.the energy of the products is less than the energy of the reactants. heat is a product.heat is a product. C(s) + 2 H 2 (g) CH 4 (g) + 18 kcal Exothermic Reactions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

13 Endothermic Reactions Heat is absorbed.Heat is absorbed. The energy of the products is greater than the energy of the reactants.The energy of the products is greater than the energy of the reactants. Heat is a reactant (added).Heat is a reactant (added). Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings N 2 (g) + O 2 (g) kcal 2NO(g)

14 Summary Reaction Energy Heat Type Change in Reaction Endothermic Heat absorbed Reactant Exothermic Heat released Product

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

16 Reaction Rate and Catalysts A catalyst increases the rate of a reaction.increases the rate of a reaction. lowers the energy of activation.lowers the energy of activation. is not used up during the reaction.is not used up during the reaction.

17 Learning Check State the effect of each on the rate of reaction as: 1) increases 2) decreases3) no change A. increasing the temperature. B. removing some of the reactants. C. adding a catalyst. D. placing the reaction flask in ice. E. increasing the concentration of one of the reactants.

18 Intermolecular Forces (Notes Only) Inter- vs. Intra- Inter- vs. Intra- Latin: Between Among Latin: Between Among molecules molecules molecules molecules Dispersion Forces Dipolar Forces Hydrogen Bonding

19 Phases of elements at STP Only 11 elements are gases Why? Intermolecular forces: forces of attraction between molecules which result in liquids and solids

20 On what do the intermolecular forces depend? Molar mass Polarity

21 Melting & Boiling Points Both are indicators of the strengths of intermolecular forces: freezing point (fp): the temperature at which a solid & liquid coexist at equilibrium under ‘normal’ pressures freezing point (fp): the temperature at which a solid & liquid coexist at equilibrium under ‘normal’ pressures boiling point (bp): the temperature at which a liquid & vapor coexist at equilibrium under ‘normal’ pressures boiling point (bp): the temperature at which a liquid & vapor coexist at equilibrium under ‘normal’ pressures Exam Questions: Rank Compounds by BPs OR Explain why one compound has a higher bp/mp than another bases on IM forces

22 Intermolecular forces: Actually all the same force! Electrostatic Electrostatic Dispersion Forces: From polarizability of atoms From polarizability of atoms Dipolar Forces: From permanent dipole moments From permanent dipole momentsHydrogen-bonding: Special case of dipolar forces Special case of dipolar forces

23 … but remember that intermolecular forces are weaker than covalent or ionic bonds!!!!

24 1. Dispersion Forces Found in all molecular substances Electrostatic in nature; arise from attractions involving induced dipoles. Magnitude depends on how easy it is to polarize the electron cloud of a molecule. larger molecules have larger polarizability. larger molecules have larger polarizability. Ask me about Geckos?

25 Polarizability increases…. with increasing MM p. 92

26 1. Dispersion Forces: Larger shapes are more polarizable Higher boiling point 

27 Intermolecular 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)

28 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) CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -SO 3 - Nonpolar Hydrophobic = “water-hating”Ionic Hydrophillic = “water loving” 1. More on London Dispersion Forces

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

30 2. Dipolar Forces: permanent dipole monents…. Higher boiling point 

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

32 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 Bonding

33 Hydrogen Bonding

34 Hydrogen Bonding

35  -  + Electron deficient H atom Electronegative atom with lone pair p. 94