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Announcements & Agenda (02/02/07) Quiz Today!!! Exam NEXT FRIDAY!!! Electron Group Covers Ch 11-5 Intermolecular Forces (Notes + bits & pieces of Ch 6) Ch 7.17.1-7.3 CHM 103 Lab Today Last Time: Molecular Shapes The Mole (5.5(5.5-5.8) Reactions Types (Especially Redox Rxns) Rxns) (5.3, 5.4) Energy of Chemical Reactions (5.9) 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 H2O Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 1 2 Last Time: Polar Molecules • contain polar bonds. • have a separation of positive and negative charge called a dipole indicated with δ+ and δ-. Chapter 5!!! Chemical Reactions • have dipoles that do not cancel! δ+ δ- •• H–Cl H—N—H dipole H dipoles do not cancel 3 4 1 Last Time: Conservation of Mass Revisited – Balanced Reactions (Ch 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 In a balanced chemical reaction • atoms are not gained or lost. • the # of reactant atoms is equal to the number of product atoms. 5 Steps in Balancing an Equation 6 Equations with Polyatomic Ions To balance the following equation, Fe3O4(s) + H2(g) Æ Fe(s Fe(s) + H2O(l O(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) Æ 3Fe( 3Fe(s) + H2O(l O(l) O: Fe3O4(s) + H2(g) Æ 3Fe(s 3Fe(s) + 4H2O(l) H: Fe3O4(s) + 4H2(g) Æ 3Fe(s 3Fe(s) + 4H2O(l O(l) 7 8 2 The “mole”…. Thinking about reactions on a realreal-world scale! Balancing with Polyatomic Ions MgCl2(aq) aq) + Na3PO4(aq) aq) Æ NaCl(aq NaCl(aq)) + Mg3(PO4)2(s) 1 mole is: Balance PO43- as a unit MgCl2(aq) aq) + 2Na3PO4(aq) aq) Æ NaCl(aq NaCl(aq)) + Mg3(PO4)2(s) 2 PO43= 2 PO43- Balance Mg and Cl 3MgCl2(aq) aq) + 2Na3PO4(aq) aq) Æ 6NaCl(aq NaCl(aq)) + Mg3(PO4)2(s) 3 Mg2+ = 3 Mg2+ + 6 Na = 6 Na+ 6 Cl = 6 Cl- 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 9 10 Collection Terms Some OneOne-mole Quantities One-Mole Quantities A collection term states a specific number of items. • 1 dozen donuts = 12 donuts • 1 ream of paper = 500 sheets • 1 case = 24 cans 32.1 g 55.9 g 58.5 g 294.2 g 342.2 g Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 11 12 3 Using Avogadro’s Number Subscripts and Moles Avogadro’s number is used to convert particles of a substance to moles. The subscripts in a formula show • the relationship of atoms in the formula. • the moles of each element in 1 mole of compound. How many moles of CO2 are in 2.50 x 1024 molecules CO2? 2.50 x 1024 molecules CO2 x Glucose C6H12O6 1 mole CO2 6.02 x 1023 molecules CO2 In 1 molecule: 6 atoms C 12 atoms H 6 atoms O In 1 mole: 6 mole C 12 mole H 6 mole O = 4.15 mole CO2 13 Molar Mass 14 Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams. • is the mass of one mole of an element or compound. • is the atomic mass expressed in grams. Remember atomic masses??? 1 mole Ag = 107.9 g 15 1 mole C = 12.01 g 1 mole S = 32.07 g 16 4 Determining the Molar Mass… Putting the mole to work in chemical reactions! 1S SO2 2O SO2 32.07 g/mol + 2 x 16.00 g/mol 64.07 g/mol For any molecule molecular mass = Σ all atomic masses 1 mole SO2 = 64.07 g SO2 17 Reading Equations In Moles Calculations Using Molar Mass Consider the following equation: 4 Fe(s + 3 O2(g) Fe(s) Molar mass factors are used to convert between the grams of a substance and the number of moles. Grams Molar mass factor 18 2 Fe2O3(s) This equation can be read in “moles” by placing the word “moles “moles”” between each coefficient and formula. Moles 4 moles Fe + 3 moles O2 19 2 moles Fe2O3 20 5 Steps in Finding the Moles and Masses in a Chemical Reaction 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 molemole-mole molar mass H2O factor mass O2 21 22 Several Types of Reactions (5.3) Calculating the Mass of a Reactant Chemical reactions can be classified as: The setup would be: • combination reactions. • decomposition reactions. 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 molemole-mole molar mass H2O factor mass O2 • single replacement reactions. • double replacement reactions. Don’t stress about these too much; be able to recognize the different flavors (see suggested problems) = 11.6 g O2 23 24 6 Oxidation-Reduction Reactions (5.4) Electron Loss and Gain An oxidationoxidation-reduction reaction An oxidationoxidation-reduction reaction • provides us with energy from food. • provides electrical energy in batteries. • occurs when iron rusts. • transfers electrons from one reactant to another. 4Fe(s 4Fe(s) + 3O2(g) • loses electrons in oxidation. Zn(s Zn(s) (LEO) Zn2+(aq) aq) + 2e- (loss of e-) • gains electrons in reduction. (GER) Cu(s Cu2+(aq) aq) + 2eCu(s) (gain of e-) 2Fe2O3(s) 25 Oxidation and Reduction 26 Writing Oxidation & Reduction Reactions Write the separate oxidation and reduction reactions for the following equation. 2Cs(s 2Cs(s) + F2(g) 2CsF(s 2CsF(s) A cesium atom loses an electron to form cesium ion. oxidation Cs(s Cs+(s) + 1e− Cs(s) Fluorine atoms gain electrons to form fluoride ions. 2F−(s) reduction F2(s) + 2e27 28 7 Collision Theory of Reactions Cu and Ag1+ 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. Cu(s) Orange metal Ag1+(aq) + 2eColorless Cu2+(aq) + 2eBlue Ag(s) Silver oxidation reduction Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 29 Activation Energy 30 Exothermic Reactions • The activation energy is the minimum energy needed for a reaction to take place. • heat is released. • the energy of the products is less than the energy of the reactants. • heat is a product. • When a collision provides energy equal to or greater than the activation energy, product can form. C(s) + 2 H2(g) 31 CH4(g) + 18 kcal Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 32 8 Endothermic Reactions Summary Reaction Energy Heat Type Change in Reaction Endothermic Heat absorbed Reactant • Heat is absorbed. • The energy of the products is greater than the energy of the reactants. • Heat is a reactant (added). Exothermic Heat released Product Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings N2(g) + O2 (g) + 43.3 kcal 2NO(g) 33 Rate of Reaction 34 Reaction Rate and Catalysts A catalyst • increases the rate of a reaction. • lowers the energy of activation. • is not used up during the 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 36 9 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 10