1. Chemistry II Stoichiometry Chapter 3

2. Stoichiometery: Calculations with Chemical Formulas and Equations

3. 1. ) What are the advantages of writing chemical formulas over writing chemical names? abbreviation important quantitative information Structural information

4. 2.)What two things is stoichiometry dependent on? 1.)Our understanding of atomic masses and 2.the Law of Conservation of mass

5. 3.) How are chemical reactions represented? By chemical equations

6. 4.) In a chemical reaction the starting substances are called reactants and the substances produced are called products.

7. 5.) The number written before the formula is called the coefficient and the number after the symbol used to indicate the number of atoms of that element in the formula is called the subscript.

8. 6.) When balancing equations which number can we change? We change the coefficient but not the subscript. Changing the coefficient changes the number of particles. Changing the subscripts changes the identity of the substance.

9. 7.) How do we indicate physical state of reactants and products? By using the following symbols: Gas (g)solid (s) Liquid (l)aqueous (aq)

10. 8.) How do we indicate that the addition of heat is necessary? By placing the delta symbol, Δ, above the arrow.

11. Balance this equation: Na(s) + H 2 O(l) → NaOH(aq) + H 2 (g)

12. Balance this equation: 2Na(s) + 2H 2 O(l) → 2NaOH(aq) + H 2 (g)

13. Balance the following: Fe + O 2 → Fe 2 O 3 C 2 H 4 + O 2 → CO 2 + H 2 O

14. Balance the following: 4Fe + 3O 2 → 2Fe 2 O 3 C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O

15. Section 2: Some Simple Patterns In this section we will review the five basic classifications of chemical reactions. Not all chemical reactions will fit neatly into one of the five classes. But, by recognizing typical patterns you will be more likely to predict products.

16. 9.) What are the five common types of reactions? Combination (synthesis) Decomposition Single replacement Double replacement combustion

17. 10.) What is a combination reaction? In a combination reaction, two or more substances react to form a single product. A + B → AB 2Mg + O 2 → 2 MgO

18. 11.) What is produced by a direct combination reaction between a metal and a nonmetal? An ionic solid 2 Li + Cl 2 → 2LiCl

19. 12.)What is a decomposition reaction? A reaction in which one substance produces two or more other substances. CaCO 3 → CaO + CO 2 2HgO → 2 Hg + O 2

20. 13.)What is a single replacement reaction? An uncombined element displaces an element that is part of a compound. The reactants in a single replacement reaction are always one compound and one element.

21. 13.)What is a single replacement reaction? contd A + BX → AX + B Mg + 2HCl → MgCl 2 + H 2

22. In a single replacement reaction, metals replace metals and nonmetals replace nonmetals. The activity series can be used to determine if a single replacement reaction will happen or not.

23. 14.)Describe a double replacement reaction. In a double replacement reactions, atoms or ions from two different compounds replace each other.

24. 14.Describe a double replacement reaction. contd A double replacement reaction will have two compounds as reactants and two compounds as products. AX + BY → AY + BX CaCO 3 + 2HCl → CaCl 2 + H 2 CO 3

25. Although most chemical reactions will fit into one of three categories, there are many that do not. Combustion reactions often do not fit into one of these categories.

26. 15.) What are combustion reactions? Rapid reactions that produce flames. Combustion reactions include O 2 as a reactant. When hydrocarbons and oxygen containing derivatives combust, they form CO 2 and H 2 O as products.

27. Write balanced equations for the following reactions: The combination reaction that occurs when lithium metal and fluorine gas react.

28. Write balanced equations for the following reactions: The combination reaction that occurs when lithium metal and fluorine gas react. 2Li + F 2 → 2LiF

29. Write balanced equations for the following reactions: The decomposition reaction that occurs when solid barium carbonate is heated. (Two products form: a solid and a gas.)

30. Write balanced equations for the following reactions: The decomposition reaction that occurs when solid barium carbonate is heated. (Two products form: a solid and a gas.) BaCO 3 → BaO + CO 2

31. Write balanced equations for the following reactions: Solid mercury(II) sulfide decomposes into its component elements when heated.

32. Write balanced equations for the following reactions: Solid mercury(II) sulfide decomposes into its component elements when heated. HgS → Hg +S

33. Write balanced equations for the following reactions: The surface of aluminum metal undergoes a combination reaction with oxygen in the air.

34. Write balanced equations for the following reactions: The surface of aluminum metal undergoes a combination reaction with oxygen in the air. 4Al + 3O 2 → 2Al 2 O 3

35. Write balanced equations for the following reactions: methanol, CH 3 OH (l), is burned in air.

36. Write balanced equations for the following reactions: methanol, CH 3 OH (l), is burned in air. 2CH 3 OH + 3O 2 → 2CO 2 + 4H 2 O

37. 16.)What is formula weight? The sum of the atomic weights of each atom in its chemical formula. Formula weights are given in a.m.u.’s

38. Calculate the formula weight of sucrose C 12 H 22 O 11

39. 342.0 amu

40. Calculate the formula weight of Ca(NO 3 ) 2

41. 164.1 amu

42. 17.)What is molecular weight? If the chemical formula is a molecule (covalently bonded) we call the formula weight “molecular weight.”

43. 18.) What are formula units? Formula units represent the chemical formula of ionic compounds. We speak of molecules for molecular compounds and formula units for ionic compounds.

44. 19.) What is percent composition? The percent by mass contributed by each element in a substance.

45. 20.) How do you calculate the % composition ? % element= (# atoms)( atomic weight) x 100 formula weight of compound

46. Calculate the % composition of C 12 H 22 O 11 %C = (12)(12 amu) X 100 = 42.1% 342.0 amu % H = (22)(1 amu) x 100 = 6.4% 342.0 amu %O = (11)(16.0 amu) x 100 = 51.5% 342.0 amu

47. Calculate the percentage of nitrogen in Ca(NO 3 ) 2

48. 17.1 %

49. Section 4 The mole # atomsmassmass Ratio of of Hof Omasses 1 1 161:16

50. Section 4 The mole # atomsmassmass Ratio of of Hof Omasses 1 1 161:16 2 2 321:16

51. Section 4 The mole # atomsmassmass Ratio of of Hof Omasses 1 1 161:16 2 2 321:16 10 10 1601:16

52. As long as the # of atoms are the same then the ratio of masses is the same as the reported atomic masses.

53. 21.) Who was Amedeo Avogadro? An Italian Chemist who determined that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

54. 22.)What is the mole? A mole is the amount of matter that contains as many objects as the number of atoms in exactly 12.0 grams of carbon-12.

55. 23.)What is Avogadro’s number? 6.02 x 10 23 1 mole of carbon 12 has 6.02 x 10 23 carbon 12 atoms.

56. What is Avogadro’s number? 6.02 x 10 23 1 mole of H 2 O has 6.02 x 10 23 water molecules.

57. What is Avogadro’s number? 6.02 x 10 23 1 mole of NaCl has 6.02 x 10 23 formula units

58. Without using a calculator, arrange the following samples in order of increasing numbers of carbon atoms: 12 g 12 C, 1 mol C 2 H 2, 9x10 23 molecules of CO 2

59. 12 g 12 C < 9x10 23 CO 2 < 1 mole C 2 H 2

60. Calculate the number of H atoms in 0.350 mol of C 6 H 12 O 6

61. ( 0.350 mole C 6 H 12 O 6 )(12 mole H/ 1 C 6 H 12 O 6 ) (6.02 x 10 23 H atoms/ 1 mole H atoms)= 2.53 x 10 24 mole H

62. How many oxygen atoms are in 0.25 mole Ca(NO 3 ) 2 ?

63. 9.0 x 10 23

64. How many oxygen atom are in 1.50 mole of sodium carbonate?

65. 2.71 x 10 24

66. Molar Mass A mole of any two objects will be the same number, but will have different masses. When we are dealing with a particular isotope of an element we use the mass of the isotope for molar mass. ( 1 mole of Carbon-12 is 12g/mol.) Otherwise, we use the atomic weight listed on the periodic table for carbon 12.0107 g/mole.

67. 24What is molar mass? The mass in grams of 1 mole of a substance. The molar mass in g/mole is numerically equal to its formula weight.

68. A single formula unit of NaCl would be 58 amu( formula mass.) A mole of NaCl formula units would be 58 gram ( molar mass)

69. What is the mass in grams of 1.000 moles of glucose C 6 H 12 O 6 ?

70. (6) (12) + (12) (1) + (6)(16) = 180 g/mole

71. Calculate the number of moles of glucose (C 6 H 12 O 6 ) in 5.380 g C 6 H 12 O 6

72. 5.380 g (1 mole C 6 H 12 O 6 / 180 g) = 0.02989 mole

73. The mole provides the bridge between mass, number and volume. diagram

74. 25.) What is the volume of any gas at STP? 1 mole of any gas will occupy a volume of 22.4L

75. Calculate the mass in grams of 0.433 mole of calcium nitrate.

76. 71.1 g Ca(NO 3 ) 2

77. What is the mass in grams of 6.33 mol of NaHCO 3

78. 532 g

79. What is the mass in grams of 3.0 x 10 -5 mole of sulfuric acid?

80. 2.9 x 10 -3 g

81. How many glucose molecules are in 5.23 g of C 6 H 12 O 6

82. 1.75 x 10 22 molecules

83. How many oxygen atoms are in this sample?

84. 1.05 x 10 23 atoms O

85. Molecular Formula from Empirical Formula If we know the molecular weight we can determine the molecular formula.

86. 28.) How do the substances in the molecular formula compare to the empirical formula. The molecular formula subscripts are always a whole number multiple of the empirical formula subscripts.

87. Mesitylene, a hydrocarbon that occurs in small amounts in crude oil, has an empirical formula of C 3 H 4. The experimentally determined molecular weight of this substance is 121 amu. What is the molecular formula of mesitylene.

88. C 3 H 4 = 36 + 4 = 40 x 3 120 C 9 H 12

89. Combustion Analysis The empirical formula of a compound is based on experiments that give the number of moles of each element in a sample of the compound.

90. 29.) What is combustion analysis? A method used to determine the empirical formula for compounds containing only hydrogen and carbon. All of the carbon is converted to carbon dioxide and all of the hydrogen is converted to water.

91. 29.) What is combustion analysis?contd The amount of CO 2 and H 2 O produced is determined by mass increase. If a third element is present, its mass can be determined by subtracting the masses of carbon and hydrogen from the original mass.

92. Isopropyl alcohol, a substance sold as rubbing alcohol is composed of C,H,and O. Combustion of 0.255 g of isopropyl alcohol produces 0.561 g of CO 2 and 0.306 g of H 2 O. Determine the empirical formula of isopropyl alcohol.

93. C3H8OC3H8O

94. Caproic acid, which is responsible for the foul odor of dirty socks, is composed of C,H and O atoms. Combustion of a 0.225 g sample of this compound produces 0.512 g of CO 2 and 0.209 g of H 2 O. A.) What is the empirical formula of caproic acid? B.) Caproic acid has a molar mass of 116 g/mol. What is its molecular formula?

95. A.) C 3 H 6 O B.) C 6 H 12 O 2

96. Section 6: Quantitative Information from Balanced Equations The coefficients in a balanced chemical equation can be interpreted both as the relative number of molecules ( or formula units) involved in the reaction and as the relative numbers of moles. The coefficients and the associated substances in a balanced equation are called stoichiometrically equivalent quantities.

97. Section 6: Quantitative Information from Balanced Equations 2H 2 + O 2 → 2H 2 O 2 mol H 2 ≈ 1 mol O 2 ≈ 2H 2 O

98. Because the substances in a balanced chemical equation are stoichiometrically equivalent, we can predict the amount of any other substance in the equation that will be needed or will be produced.

99. 30.) Predict the moles of H 2 O that will be produced from 1.57 mol of O 2 ? 3.14 mole H 2 O

100. 31.) To predict the amount of any other substance that will be needed or will be produced follow these steps: 1.) Convert known value into moles. 2.) Convert from moles of your known to moles of your unknown by using the coefficient in your balanced equation 3.) Convert from moles of unknown to the value requested.

101. 32.) Calculate the mass of CO 2 produced when 1.00 gram of C 4 H 10 is burned. 3.03 g CO 2

102. How many grams of water are produced in the oxidation of 1.00 gram of glucose, C 6 H 12 O 6 ?.6 g C 6 H 12 O 6

103. The decomposition of KClO3 is commonly used to prepare small amounts of O2 in the laboratory: 2KClO 3(s) → 2KCl (s) + 3O 2(g) How many grams of O 2 can be prepared from 4.5 g of KClO 3 ? 1.8 g O 2

104. Solid lithium hydroxide is used in space vehicles to remove the carbon dioxide to form solid carbonate and liquid water. How many grams of carbon dioxide can be absorbed by 1.00 g of lithium hydroxide.

105. .919 g carbon dioxide

106. Propane, C 3 H 8, is a common fuel used for cooking and home heating. What mass of O 2 is consumed in the combustion of 1.00 g propane?

107. 3.64 g

108. Section 7: Limiting Reactants In chemical reactions when one reactant is totally consumed the reaction stops.

109. 33.) What is the limiting reactant? The reactant that is completely consumed in a reaction.

110. 34.) Which reactant determines the amount of product that can be formed ? Limiting reactant

111. 35.) What do we call the other reactants? The reactants in excess

112. The most important commercial process for converting N 2 from the air into nitrogen containing compounds is based on the reaction of N 2 and H 2 to form ammonia (NH 3 ) : How many mole of NH 3 can be formed from 3.0 mole of N 2 and 6.0 mole of H 2 N 2 + 3H 2 → 2NH 3

113. 4 mole of NH 3

114. Consider the reaction 2Al + 3Cl 2 → 2AlCl 3 A mixture of 1.50 mole of Al and 3.00 mole of Cl 2 is allowed to react. (a) Which is the limiting reactant? (b) how many moles of AlCl 3 are formed? ( c) How many moles of the excess reactant remain at the end of the reaction?

115. a.) Al b.) 1.5 mole of AlCl 3 c.).75 mole Cl 2 remain.

116. Consider the following reaction that occurs in a fuel cell: 2 H 2 + O 2 → 2H 2 O This reaction, done properly, produces energy in the form of electricity and water. Suppose a fuel cell is set up with 150 g of hydrogen gas and 1500 grams of oxygen gas. ( each measurement is given with two significant figures). How many grams of water can be formed?

117. 1400 grams of water.

118. When working with limiting reactant problems, you will need to pick one product, determine the number of moles of that product that will be produced by each reactant. The reactant that gives the smallest amount number is the limiting reactant and determines the amount of product that can be formed.

119. A strip of zinc metal with a mass of 2.00 g is placed in an aqueous solution containing 2.50 g of silver nitrate, causing the following reaction to occur: Zn + 2AgNO 3 → 2Ag + Zn(NO 3 ) 2

120. a.) Which reactant is the limiting reactant? b) How many grams of Ag will form? c.) How many grams of Zn(NO 3 ) 2 will form? d) How many grams of the excess reactant will be left at the end of the reaction?

121. Zn + 2AgNO 3 → 2Ag + Zn(NO 3 ) 2 a.) AgNO 3 b) 1.6 g Ag c.) 1.39 g of Zn(NO 3 ) 3 d)1.53 g Zn left over.

122. 36. What is the theoretical yield? The quantity of product that is calculated to form when all of the limiting reactant reacts.

123. 37.) What is the actual yield? The amount of product that actually forms.

124. 38.) What is the percent yield? A comparison of the amounts of product that formed to the amount you expect to form. % yield = Actual x 100 Theorectical