1 Announcements & Agenda (02/02/07) Quiz Today!!! Exam NEXT FRIDAY!!! Covers Ch 1-5 Covers Ch 1-5 Intermolecular Forces (Notes + bits & pieces of Ch 6) Intermolecular Forces (Notes + bits & pieces of Ch 6) Ch Ch CHM 103 Lab CHM 103 LabToday The Mole ( ) The Mole ( ) Reactions Types (Especially Redox Rxns) (5.3, 5.4) Reactions Types (Especially Redox Rxns) (5.3, 5.4) Energy of Chemical Reactions (5.9) Energy of Chemical Reactions (5.9)

2 Electron Group Bonded Atoms Lone Pairs Bond Angles Molecular Shape Example440109tetrahedral CH 4 431~109Pyramidal NH 3 422~109Bent H2OH2OH2OH2O Last Time: Molecular Shapes Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

3 Last Time: Polar Molecules contain polar bonds.contain polar bonds. have a separation of positive and negative charge called a dipole indicated with  + and  -.have a separation of positive and negative charge called a dipole indicated with  + and  -. have dipoles that do not cancel!have dipoles that do not cancel!  +  -  +  - H–Cl H — N — H dipole dipole dipoles do not cancel dipoles do not cancel H

4 Chapter 5!!! Chemical Reactions

5 24 Good Practice Problems (Ch 5) 5.01, 5.05, 5.07, 5.11, 5.13, 5.17, 5.25, 5.27, 5.33, 5.37, 5.41, 5.47, 5.57, 5.69, 5.73, 5.75, 5.79, 5.81, 5.83, 5.85, 5.91, 5.93, 5.95, 5.97

6 Last Time: Conservation of Mass Revisited – Balanced Reactions (Ch 5) In a balanced chemical reaction atoms are not gained or lost.atoms are not gained or lost. the # of reactant atoms is equal to the number of product atoms.the # of reactant atoms is equal to the number of product atoms.

7 To balance the following equation, Fe 3 O 4 (s) + H 2 (g)  Fe(s) + H 2 O(l) work on one element at a time.work on one element at a time. use only coefficients in front of formulas.use only coefficients in front of formulas. do not change any subscripts.do not change any subscripts. Fe:Fe 3 O 4 (s) + H 2 (g)  3Fe(s) + H 2 O(l) O:Fe 3 O 4 (s) + H 2 (g)  3Fe(s) + 4H 2 O(l) H: Fe 3 O 4 (s) + 4H 2 (g)  3Fe(s) + 4H 2 O(l) Steps in Balancing an Equation

8 Equations with Polyatomic Ions

9 Balancing with Polyatomic Ions MgCl 2 (aq) + Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) Balance PO 4 3- as a unit MgCl 2 (aq) + 2Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) MgCl 2 (aq) + 2Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 2 PO 4 3- = 2 PO PO 4 3- = 2 PO 4 3- Balance Mg and Cl 3MgCl 2 (aq) + 2Na 3 PO 4 (aq)  6NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 3 Mg 2+ = 3 Mg 2+ 3 Mg 2+ = 3 Mg 2+ 6 Na + = 6 Na + 6 Na + = 6 Na + 6 Cl - = 6 Cl - 6 Cl - = 6 Cl -

10 The “mole”…. Thinking about reactions on a real-world scale! The “mole”…. Thinking about reactions on a real-world scale!  1 mole is:  a collection of stuff that equals the # of atoms present in exactly g of 12 C (6.022  atoms)  always  somethings (Avogodro’s #, N A )  New term: Molar Mass (MM)  the mass of 1 mol of an element/compound in gms.  e.g. the MM of 12 C is g/mol  b/c 1 mol is defined as  atoms, the MM for any element can be determined

11 Collection Terms A collection term states a specific number of items. 1 dozen donuts1 dozen donuts = 12 donuts 1 ream of paper1 ream of paper = 500 sheets 1 case = 24 cans1 case = 24 cans Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

12 Some One-mole Quantities 32.1 g 55.9 g 58.5 g g g 32.1 g 55.9 g 58.5 g g g One-Mole Quantities

13 Avogadro’s number is used to convert particles of a substance to moles. How many moles of CO 2 are in 2.50 x molecules CO 2 ? 2.50 x molecules CO 2 x 1 mole CO x molecules CO x molecules CO 2 = 4.15 mole CO 2 Using Avogadro’s Number

14 Subscripts and Moles The subscripts in a formula show the relationship of atoms in the formula.the relationship of atoms in the formula. the moles of each element in 1 mole of compound.the moles of each element in 1 mole of compound.Glucose C 6 H 12 O 6 In 1 molecule: 6 atoms C 12 atoms H6 atoms O In 1 mole: 6 mole C 12 mole H 6 mole O

15 Molar Mass is the mass of one mole of an element or compound.is the mass of one mole of an element or compound. is the atomic mass expressed in grams.is the atomic mass expressed in grams.

16 Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams. Remember atomic masses??? 1 mole Ag 1 mole C 1 mole S = g = g = g

17 Determining the Molar Mass… SO 2 1S32.07 g/mol 2O+ 2 x g/mol SO g/mol For any molecule molecular mass =  all atomic masses 1 mole SO 2 = g SO 2

18 Putting the mole to work in chemical reactions!

19 Molar mass factors are used to convert between the grams of a substance and the number of moles. Calculations Using Molar Mass Grams Molar mass factor Moles

20 Consider the following equation: 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3 (s) This equation can be read in “moles” by placing the word “moles” between each coefficient and formula. 4 moles Fe + 3 moles O 2 2 moles Fe 2 O 3 Reading Equations In Moles

21 Steps in Finding the Moles and Masses in a Chemical Reaction

22 The reaction between H 2 and O 2 produces 13.1 g water. How many grams of O 2 reacted? How many grams of O 2 reacted? 2 H 2 (g) + O 2 (g) 2 H 2 O (g) ? g 13.1 g ? g 13.1 g The plan and factors would be g H 2 O mole H 2 O mole O 2 g O 2 g H 2 O mole H 2 O mole O 2 g O 2 molar mole-mole molar molar mole-mole molar mass H 2 O factor mass O 2 mass H 2 O factor mass O 2 Calculating the Mass of a Reactant

23 Calculating the Mass of a Reactant The setup would be: 13.1 g H 2 O x 1 mole H 2 O x 1 mole O 2 x 32.0 g O g H 2 O 2 moles H 2 O 1 mole O 2 molar mole-mole molar molar mole-mole molar mass H 2 O factor mass O 2 mass H 2 O factor mass O 2 = 11.6 g O 2 = 11.6 g O 2

24 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)

25 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)

26 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

27 Oxidation and Reduction

28 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

29 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!

30 Collision Theory of Reactions 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

31 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.

32 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

33 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)

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

35 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.

36 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.

37 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.