Chapter 31 Stoichiometry Mrs. Weston Seneca Valley SHS

Chapter 32 Stoichiometry - The study of quantities of materials consumed and produced in chemical reactions. Stoichiometric coefficients: numbers in front of the chemical formulas; give ratio of reactants and products. Chemical Equations

Chapter 33 Which of the following correctly describes the balanced chemical equation given below? There may be more than one true statement. If a statement is incorrect, explain what is incorrect about it. 4Al + 3O 2  2Al 2 O 3 I. For every 4 atoms of aluminum that react with 6 atoms of oxygen, 2 molecules of aluminum oxide are produced. II. For every 4 moles of aluminum that react with 3 moles of oxygen, 2 moles of aluminum oxide are produced.| III. For every 4 grams of aluminum that react with 3 grams of oxygen, 2 grams of aluminum oxide are produced. React

Chapter 34 Which of the following statements are true concerning balanced chemical equations? There may be more than one true statement. I. The number of molecules is conserved. II. The coefficients tell you how much of each substance you have. III.Atoms are neither created nor destroyed. IV.The coefficients indicate the mass ratios of the substances used. V.The sum of the coefficients on the reactant side equals the sum of the coefficients on the product side. React

Chapter 35 The Atomic Mass Scale 1 H weighs x g and 16 O x g. We define: mass of 12 C = exactly 12 amu. Using atomic mass units: 1 amu = x g 1 g = x amu Atomic and Molecular Weights

Chapter 36 Average Atomic Mass Relative atomic mass: average masses of isotopes: Naturally occurring C: % 12 C % 13 C. Average mass of C: ( )(12 amu) + (0.0108)(13 amu) = amu. Atomic weight (AW) is also known as average atomic mass (atomic weight). Atomic weights are listed on the periodic table. Atomic and Molecular Weights

Chapter 37 Formula and Molecular Weights Formula weights (FW): sum of AW for atoms in formula. FW (H 2 SO 4 ) = 2AW(H) + AW(S) + 4AW(O) = 2(1.0 amu) + (32.0 amu) + 4(16.0) = 98.0 amu Molecular weight (MW) is the weight of the molecular formula. MW(C 6 H 12 O 6 ) = 6(12.0 amu) + 12(1.0 amu) + 6(16.0 amu) Atomic and Molecular Weights

Chapter 38 Percentage Composition from Formulas Percent composition is the atomic weight for each element divided by the formula weight of the compound multiplied by 100: For iron in iron (III) oxide (Fe 2 O 3 ) Atomic and Molecular Weights

Chapter 39 Percentage Composition from Formulas Atomic and Molecular Weights Find the percent composition of carvone (C 10 H 14 O), an organic molecule responsible for the smell of spearmint oil.

Chapter 310 Mole: convenient measure chemical quantities. 1 mole of something = x of that thing. Experimentally, 1 mole of 12 C has a mass of exactly 12 g. Molar Mass Molar mass: mass in grams of 1 mole of substance (units g/mol). Mass of 1 mole of 12 C = 12 g ex: CO 2 = grams per mole The Mole

Chapter 311 Molar Mass Molar mass: sum of the molar masses of the atoms: molar mass of N 2 = 2 x (molar mass of N). Molar masses for elements are found on the periodic table. Formula weights are numerically equal to the molar mass. The Mole

Chapter 312 Interconverting Masses, Moles, and Numbers of Particles The Mole

Chapter 313 Interconverting Masses, Moles, and Numbers of Particles A certain sample of calcium carbonate contains 4.86 moles. What is the mass of the sample? How many carbonate ions are present? The Mole

Chapter 314 Start with mass % of elements (i.e. empirical data) and calculate a formula, or Start with the formula and calculate the mass % elements. Empirical Formulas from Analyses

Chapter 315 Molecular Formula from Empirical Formula Determine the empirical and molecular formulas of a compound that gives the following analysis (in mass percents):71.65% Cl 24.27% C 4.07% H The molar mass is known to be g/mol. Empirical Formulas from Analyses

Chapter 316 Molecular Formula from Empirical Formula Caffeine contains 49.48% carbon, 5.15% hydrogen, 28.87% nitrogen, and 16.49% oxygen. The molar mass is g/mol. Determine the molecular formula of caffeine. Empirical Formulas from Analyses

Chapter 317 Combustion Analysis Empirical formulas are determined by combustion analysis: This is a schematic diagram of the combustion device used to analyze substances for carbon and hydrogen. : Empirical Formulas from Analyses

Chapter 318 Writing a Chemical Equation Chemical symbols give a “before-and-after” picture of a chemical reaction ReactantsProducts MgO (s) + C (s) CO (g) + Mg (s) magnesium oxide to form carbon monoxide reacts with carbon and magnesium

Chapter 319 Balance Equations with Coefficients Coefficients in front of formulas balance each type of atom 4NH 3 + 5O 2 4NO + 6H 2 O 4 N = 4 N 12 H=12 H 10 O=10 O Symbols used in chemical reactions: (g) (l) (s) (aq)  e -

Chapter 320 The ratio of grams of reactant cannot be directly related to the grams of product. Quantitative Information from Balanced Equations

Chapter 321 Quantitative Information from Balanced Equations Solid lithium hydroxide is used in space vehicles to remove exhaled carbon dioxide from the living environment by forming solid lithium carbonate and liquid water. What mass of gaseous carbon dioxide can be absorbed by 1.00 kg of lithium hydroxide?

Chapter 322 If the reactants are not present in stoichiometric amounts, at end of reaction some reactants are still present (in excess). Limiting Reactant: one reactant that is consumed before the other reactant(s) thus limiting the amount of product Limiting Reactants

Chapter 323 Theoretical Yields The amount of product predicted from stoichiometry taking into account limiting reagents is called the theoretical yield. The percent yield relates the actual yield (amount of material recovered in the laboratory) to the theoretical yield: Limiting Reactants

Chapter 324 Theoretical Yields Methanol, CH 3 OH, is used as a fuel in race cars and is also a potential replacement for gasoline. It can be manufactured by combining carbon monoxide and hydrogen gases. Suppose 68.5 kg CO is reacted with 8.60 kg H 2. Which reactant is limiting? What is the theoretical yield? If 3.57 x10 4 g is actually produced, what is the percent yield of methanol? Limiting Reactants

Chapter 325 End of Chapter 3