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Chapter 6

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  1. Chapter 6 Chemical Reactions • Classification and Mass Relationship

  2. Physical and Chemical Change In a physical change, • The identity and composition of the substance do not change. • The state can change or the material can be torn into smaller pieces. In a chemical change, • New substances form with different compositions and properties. • A chemical reaction takes place.

  3. Physical and Chemical Change

  4. Some Examples of Chemical and Physical Changes

  5. Learning Check Classify each of the following as a 1) physical change or 2) chemical change A. ____ Burning a candle. B. ____ Ice melting on the street. C. ____ Toasting a marshmallow. D. ____ Cutting a pizza. E. ____ Polishing a silver bowl.

  6. Solution Classify each of the following as a 1) physical change or 2) chemical change A. 2 Burning a candle. B. 1 Ice melting on the street. C. 2 Toasting a marshmallow. D. 1 Cutting a pizza. E. 2 Polishing a silver bowl.

  7. Chemical Reaction • In a chemical reaction, a chemical change produces one or more new substances. • During a reaction, old bonds are broken and new bonds are formed.

  8. Chemical Reaction • In a chemical reaction, atoms in the reactants are rearranged to form one or more different substances. • In this reaction, Fe and O2 react to form rust (Fe2O3). 4Fe + 3O2 2Fe2O3

  9. Writing a Chemical Equation • A chemical equation • Shows the chemical formulas of the reactants to the left of an arrow and the products on the right.Reactants ProductsMgO + C CO + Mg • Can be read in words. “Magnesium oxide reacts with carbon to formcarbon monoxide and magnesium.”

  10. Symbols Used in Equations • Symbols used in equations show the states of the reactants and products and the reaction conditions.

  11. Quantities in A Chemical Reaction 4 NH3 + 5 O2 4 NO + 6 H2O Four molecules of NH3 react with five molecules of O2 to produce four molecules of NO and six molecules of H2O. or Four moles of NH3 react with 5 moles of O2 to produce four moles of NO and six moles of H2O.

  12. Law of Conservation of Mass • In any ordinary chemical reaction, matter is not created nor destroyed. + + H2 + Cl2 2 HCl= Total Mass 2(1.0) + 2(35.5) 2(36.5) 73.0 g = 73.0 g

  13. 6.2 Balancing a Chemical Equation • A chemical equation is balanced when there are the same numbers of each type of atom on both sides of the equation. Al + S Al2S3 Not Balanced 2Al + 3S Al2S3Balanced

  14. Using Coefficients to Balance • To balance an equation, place coefficientsin front of the appropriate formulas. 4 NH3 + 5 O24 NO + 6 H2O • Check the balance by counting the atoms of each element in the reactants and the products. 4 N (4 x 1N) = 4 N (4 x 1N) 12 H (4 x 3H) = 12 H (6 x 2H) 10 O (5 x 2O) = 10 O (4O + 6O)

  15. Learning Check Check the balance of atoms in the following: Fe3O4 + 4 H2 3 Fe +4H2O A. Number of H atoms in products. 1) 2 2) 4 3) 8 B. Number of O atoms in reactants. 1) 2 2) 4 3) 8 C. Number of Fe atoms in reactants. 1) 1 2) 3 3) 4

  16. Solution Fe3O4 + 4 H2 3 Fe +4H2O • Number of H atoms in products. 3) 8 (4H2O) B. Number of O atoms in reactants. 2) 4 (Fe3O4) C. Number of Fe atoms in reactants. 2) 3 (Fe3O4)

  17. Balancing with Polyatomic Ions • Polyatomic ions can be balanced as a unit when they appear on both sides. Pb(NO3)2 + NaCl NaNO3 + PbCl2 • Balance NO3- as a unit Pb(NO3)2 + NaCl 2NaNO3 + PbCl2 2 NO3– = 2 NO3– • Balance Na (or Cl) Pb(NO3)2 + 2NaCl 2NaNO3 + PbCl2 2Na+ = 2Na+ 2Cl– = 2Cl–

  18. Learning Check Balance each equation. The coefficients in the answers are read from left to right. __Mg + __N2 __Mg3N2 1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1 B. __Al + __Cl2 __AlCl3 1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, 2

  19. Solution A. 3) 3, 1, 1 3 Mg + 1 N21 Mg3N2 B. 3) 2, 3, 2 2 Al + 3 Cl22 AlCl3

  20. Collection Terms • A collection term indicates a specific number of items. • For example, 1 dozen doughnuts contains 12 doughnuts. • 1 ream of paper means 500 sheets. • 1 case is 24 cans.

  21. A Mole • A mole contains 6.02 x 1023 particles, which is the number of carbon atoms in 12.01 g of carbon. 1 mole C = 6.02 x 1023 C atoms • The number 6.02 x 1023 is known as Avogadro’s number. • One mole of any element contains Avogadro’s number of atoms. 1 mole Na = 6.02 x 1023 Na atoms 1 mole Au = 6.02 x 1023 Au atoms

  22. A Mole of Molecules • Avogadro’s number is also the number of molecules and formula units in one mole of a compound. • One mole of a covalent compound contains Avogadro’s number of molecules. 1 mole CO2 = 6.02 x 1023CO2 molecules 1 mole H2O = 6.02 x 1023H2O molecules • One mole of an ionic compound contains Avogadro’s number of formula units. 1 mole NaCl = 6.02 x 1023 NaCl formula units

  23. Samples of One Mole Quantities

  24. Learning Check A. Calculate the number of atoms in 2.0 moles of Al. 1) 2.0 Al atoms 2) 3.0 x 1023 Alatoms 3) 1.2 x 1024 Al atoms B. Calculate the number of moles of S in 1.8 x 1024 S. 1) 1.0 mole S atoms 2) 3.0 mole S atoms 3) 1.1 x 1048 mole S atoms

  25. Solution A. Calculate the number of atoms in 2.0 moles of Al. 3) 1.2 x 1024 Al atoms 2.0 moles Al x 6.02 x 1023 Al atoms 1 mole Al B. Calculate the number of moles of S in 1.8 x 1024 S. 2) 3.0 mole S 1.8 x 1024 S atoms x 1 mole S 6.02 x 1023 S atoms

  26. Molar Mass • The mass of one mole is called molar mass. • The molar mass of an element is the atomic mass expressed in grams.

  27. Learning Check Give the molar mass to the nearest 0.1 g. A. 1 mole of K atoms = ________ B. 1 mole of Sn atoms = ________

  28. Solution Give the molar mass to the nearest 0.1 g. A. 1 mole of K atoms = 39.1 g B. 1 mole of Sn atoms = 118.7 g

  29. Molar Mass of CaCl2 • For a compound, the molar mass is the sum of the molar masses of the elements in the formula. We calculate the molar mass of CaCl2 to the nearest 0.1 g as follows.

  30. Molar Mass of K3PO4 Determine the molar mass of K3PO4 to 0.1 g.

  31. One-Mole Quantities 32.1 g 55.9 g 58.5 g 294.2 g 342.3 g

  32. Learning Check A. 1 mole of K2O = ______g B. 1 mole of antacid Al(OH)3 = ______g

  33. Solution A. 1 mole of K2O 2 moles K (39.1 g/mole) + 1 mole O (16.0 g/mole) 78.2 g + 16.0 g = 94.2 g B. 1 mole of antacid Al(OH)3 1 mole Al (27.0 g/mole) + 3 moles O (16.0 g/mole) + 3 moles H (1.0 g/mole) 27.0 g + 48.0 g + 3.0 g = 78.0 g

  34. Learning Check Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 1) 40.0 g/mole 2) 262 g/mole 3) 309 g/mole

  35. Solution Prozac, C17H18F3NO, is a widely used antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 3) 309 g/mole 17C (12.0) + 18H (1.0) + 3F (19.0) + 1N (14.0) + 1 O (16.0) = 204 + 18 + 57.0 + 14.0 + 16.0

  36. Molar Mass Factors Methane CH4 known as natural gas is used in gas cook tops and gas heaters. 1 mole CH4 = 16.0 g The molar mass of methane can be written as conversion factors. 16.0 g CH4 and 1 mole CH4 1 mole CH4 16.0 g CH4

  37. Learning Check Acetic acid C2H4O2 gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid.

  38. Solution Acetic acid C2H4O2 gives the sour taste to vinegar. Write two molar mass factors for acetic acid. 1 mole of acetic acid = 60.0 g acetic acid 1 mole acetic acid and 60.0 g acetic acid 60.0 g acetic acid 1 mole acetic acid

  39. Calculations with Molar Mass • Mole factors are used to convert between the grams of a substance and the number of moles. Mole factor Grams Moles

  40. Calculating Grams from Moles Aluminum is often used for the structure of lightweight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al x 27.0 g Al = 81.0 g Al 1 mole Al mole factor for Al

  41. Learning Check The artificial sweetener aspartame (Nutri-Sweet) C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame?

  42. Solution Calculate the molar mass of C14H18N2O5. (14 x 12.0) + (18 x 1.0) + (2 x 14.0) + (5 x 16.0) = 294 g/mole Set up the calculation using a mole factor. 225 g aspartame x 1 mole aspartame 294 g aspartame mole factor(inverted) = 0.765 mole aspartame

  43. Conservation of Mass • In a chemical reaction, the mass of the reactants is equal to the mass of the products.2 moles Ag + 1 mole S = 1 mole Ag2S2 (107.9 g) + 1(32.0 g) = 1 (247.9 g) 247.9 g reactants = 247.9 g product

  44. Moles in Equations • We can read the equation in “moles” by placing the word “moles” between each coefficient and formula.4 Fe + 3 O2 2 Fe2O34 moles Fe + 3 moles O2 2 moles Fe2O3 223.2g 96 g 319.2

  45. Writing Mole-Mole Factors • A mole-mole factor is a ratio of the coefficients for two substances. 4 Fe + 3 O2 2 Fe2O3 Fe and O24 mole Fe and 3 mole O2 3 mole O2 4 mole Fe Fe and Fe2O3 4 mole Fe and 2 mole Fe2O3 2 mole Fe2O3 4 mole Fe O2 and Fe2O3 3 mole O2 and 2 mole Fe2O3 2 mole Fe2O3 3 mole O2

  46. Learning Check Consider the following equation: 3 H2 + N2 2 NH3 A. A mole factor for H2 and N2 is 1) 3 mole N22) 1 mole N2 3) 1 mole N2 1 mole H2 3 mole H2 2 mole H2 B. A mole factor for NH3 and H2 is 1) 1 mole H2 2) 2 mole NH3 3) 3 mole N2 2 mole NH3 3 mole H2 2 mole NH3

  47. Solution 3 H2 + N2 2 NH3 A. A mole factor for H2 and N2 is 2) 1 mole N2 3 mole H2 B. A mole factor for NH3 and H2 is 2) 2 mole NH3 3 mole H2

  48. Calculations with Mole Factors Consider the following reaction: 4 Fe + 3 O2 2 Fe2O3 How many moles of Fe2O3 are produced when 6.0 moles O2 react? Use the appropriate mole factor to determine the moles Fe2O3. 6.0 mole O2 x 2 mole Fe2O3 = 4.0 mole Fe2O3 3 mole O2

  49. Mass Calculations

  50. 2CH3OH + 3O2 2CO2 + 4H2O grams CH3OH moles CH3OH moles H2O grams H2O 4 mol H2O 18.0 g H2O 1 mol CH3OH x = x x 2 mol CH3OH 32.0 g CH3OH 1 mol H2O Methanol (CH3OH) burns in air according to the equation If 209 g of methanol are used up in the combustion, what mass of water is produced? molar mass CH3OH molar mass H2O coefficients chemical equation 209 g CH3OH 235 g H2O