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Announcements & Agenda (02/02/07) Quiz Today!!! Exam NEXT FRIDAY!!! Covers Ch 1-5 Intermolecular Forces (Notes + bits & pieces of Ch 6) Ch 7.1-7.3 CHM 103 Lab Today The Mole (5.5-5.8) Reactions Types (Especially Redox Rxns) (5.3, 5.4) Energy of Chemical Reactions (5.9) 1 Last Time: Molecular Shapes Electron Group Bonded Lone Bond Molecular Atoms Pairs Angles Shape Example 4 4 0 109 tetrahedral CH4 4 3 1 ~109 Pyramidal NH3 4 2 2 ~109 Bent H 2O Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 2 Last Time: Polar Molecules • contain polar bonds. • have a separation of positive and negative charge called a dipole indicated with + and -. • have dipoles that do not cancel! + - •• H–Cl H—N—H dipole H dipoles do not cancel 3 Chapter 5!!! Chemical Reactions 4 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 5 Last Time: Conservation of Mass Revisited – Balanced Reactions (Ch 5) In a balanced chemical reaction • atoms are not gained or lost. • the # of reactant atoms is equal to the number of product atoms. 6 Steps in Balancing an Equation To balance the following equation, Fe3O4(s) + H2(g) Fe(s) + H2O(l) • work on one element at a time. • use only coefficients in front of formulas. • do not change any subscripts. Fe: Fe3O4(s) + H2(g) 3Fe(s) + H2O(l) O: Fe3O4(s) + H2(g) 3Fe(s) + 4H2O(l) H: Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l) 7 Equations with Polyatomic Ions 8 Balancing with Polyatomic Ions MgCl2(aq) + Na3PO4(aq) NaCl(aq) + Mg3(PO4)2(s) Balance PO43- as a unit MgCl2(aq) + 2Na3PO4(aq) NaCl(aq) + Mg3(PO4)2(s) 2 PO43= 2 PO43Balance Mg and Cl 3MgCl2(aq) + 2Na3PO4(aq) 6NaCl(aq) + Mg3(PO4)2(s) 3 Mg2+ = 3 Mg2+ 6 Na+ = 6 Na+ 6 Cl= 6 Cl9 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 12.000 g of 12C (6.022 1023 atoms) always 6.022 1023 somethings (Avogodro’s #, NA) New term: Molar Mass (MM) the mass of 1 mol of an element/compound in gms. e.g. the MM of 12C is 12.000 g/mol b/c 1 mol is defined as 6.022 1023 atoms, the MM for any element can be determined 10 Collection Terms A collection term states a specific number of items. • 1 dozen donuts = 12 donuts • 1 ream of paper = 500 sheets • 1 case = 24 cans Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 11 Some One-mole Quantities One-Mole Quantities 32.1 g 55.9 g 58.5 g 294.2 g 342.2 g 12 Using Avogadro’s Number Avogadro’s number is used to convert particles of a substance to moles. How many moles of CO2 are in 2.50 x 1024 molecules CO2? 2.50 x 1024 molecules CO2 x 1 mole CO2 6.02 x 1023 molecules CO2 = 4.15 mole CO2 13 Subscripts and Moles The subscripts in a formula show • the relationship of atoms in the formula. • the moles of each element in 1 mole of compound. Glucose C6H12O6 In 1 molecule: 6 atoms C 12 atoms H 6 atoms O In 1 mole: 6 mole C 12 mole H 6 mole O 14 Molar Mass • is the mass of one mole of an element or compound. • is the atomic mass expressed in grams. 15 Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams. Remember atomic masses??? 1 mole Ag = 107.9 g 1 mole C = 12.01 g 1 mole S = 32.07 g 16 Determining the Molar Mass… 1S SO2 2O SO2 32.07 g/mol + 2 x 16.00 g/mol 64.07 g/mol For any molecule molecular mass = S all atomic masses 1 mole SO2 = 64.07 g SO2 17 Putting the mole to work in chemical reactions! 18 Calculations Using Molar Mass Molar mass factors are used to convert between the grams of a substance and the number of moles. Grams Molar mass factor Moles 19 Reading Equations In Moles Consider the following equation: 4 Fe(s) + 3 O2(g) 2 Fe2O3(s) This equation can be read in “moles” by placing the word “moles” between each coefficient and formula. 4 moles Fe + 3 moles O2 2 moles Fe2O3 20 Steps in Finding the Moles and Masses in a Chemical Reaction 21 Calculating the Mass of a Reactant The reaction between H2 and O2 produces 13.1 g water. How many grams of O2 reacted? 2 H2(g) + O2(g) 2 H2O (g) ?g 13.1 g The plan and factors would be g H2O mole H2O mole O2 g O2 molar mole-mole molar mass H2O factor mass O2 22 Calculating the Mass of a Reactant The setup would be: 13.1 g H2O x 1 mole H2O x 1 mole O2 x 32.0 g O2 18.0 g H2O 2 moles H2O 1 mole O2 molar mole-mole molar mass H2O factor mass O2 = 11.6 g O2 23 Several Types of Reactions (5.3) Chemical reactions can be classified as: • combination reactions. • decomposition reactions. • single replacement reactions. • double replacement reactions. Don’t stress about these too much; be able to recognize the different flavors (see suggested problems) 24 Oxidation-Reduction Reactions (5.4) An oxidation-reduction reaction • provides us with energy from food. • provides electrical energy in batteries. • occurs when iron rusts. 4Fe(s) + 3O2(g) 2Fe2O3(s) 25 Electron Loss and Gain An oxidation-reduction reaction • transfers electrons from one reactant to another. • loses electrons in oxidation. Zn(s) (LEO) Zn2+(aq) + 2e- (loss of e-) • gains electrons in reduction. (GER) Cu2+(aq) + 2eCu(s) (gain of e-) 26 Oxidation and Reduction 27 Writing Oxidation & Reduction Reactions Write the separate oxidation and reduction reactions for the following equation. 2Cs(s) + F2(g) 2CsF(s) A cesium atom loses an electron to form cesium ion. Cs(s) Cs+(s) + 1e− oxidation Fluorine atoms gain electrons to form fluoride ions. F2(s) + 2e2F−(s) reduction 28 Cu and Ag1+ COOL DEMO! Cu(s) Orange metal Ag1+(aq) + 2eColorless Cu2+(aq) + 2eBlue Ag(s) Silver oxidation reduction 29 Collision Theory of Reactions A chemical reaction occurs when • collisions between molecules have sufficient energy to break the bonds in the reactants. • bonds between atoms of the reactants (N2 and O2) are broken and new bonds (NO) can form. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 30 Activation Energy • 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. 31 Exothermic Reactions • heat is released. • the energy of the products is less than the energy of the reactants. • heat is a product. C(s) + 2 H2(g) CH4(g) + 18 kcal Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 32 Endothermic Reactions • Heat is absorbed. • The energy of the products is greater than the energy of the reactants. • Heat is a reactant (added). Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings N2(g) + O2 (g) + 43.3 kcal 2NO(g) 33 Summary Reaction Energy Heat Type Change in Reaction Endothermic Heat absorbed Reactant Exothermic Heat released Product 34 Rate of Reaction • is the speed at which reactant is used up. • is the speed at which product forms. • increases when temperature rises because reacting molecules move faster providing more colliding molecules with energy of activation. 35 Reaction Rate and Catalysts A catalyst • increases the rate of a reaction. • lowers the energy of activation. • is not used up during the reaction. 36 Learning Check State the effect of each on the rate of reaction as: 1) increases 2) decreases 3) 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. 37