Reaction Stoichiometry Quiz

PDF page 207: A balanced chemical equation provides a great deal of information in a very succinct format. Chemical formulas provide the identities of the reactants and products involved in the chemical change, allowing classification of the reaction. Coefficients provide the relative numbers of these chemical species, allowing a quantitative assessment of the relationships between the amounts of substances consumed and produced by the reaction. These quantitative relationships are known as the reaction’s stoichiometry, a term derived from the Greek words stoicheion (meaning “element”) and metron (meaning “measure”). In this module, the use of balanced chemical equations for various stoichiometric applications is explored. The general approach to using stoichiometric relationships is similar in concept to the way people go about many common activities. Food preparation, for example, offers an appropriate comparison. A recipe for making eight 3 pancakes calls for 1 cup pancake mix, cup milk, and one egg. The “equation” representing the preparation of 4 pancakes per this recipe is 3 1 cup mix + cup milk + 1 egg ⟶ 8 pancakes 4 If two dozen pancakes are needed for a big family breakfast, the ingredient amounts must be increased proportionally according to the amounts given in the recipe. For example, the number of eggs required to make 24 pancakes is 1 egg 24 pancakes × = 3 eggs 8 pancakes Balanced chemical equations are used in much the same fashion to determine the amount of one reactant required to react with a given amount of another reactant, or to yield a given amount of product, and so forth. The coefficients in the balanced equation are used to derive stoichiometric factors that permit computation of the desired quantity. To illustrate this idea, consider the production of ammonia by reaction of hydrogen and nitrogen: N (g) + 3H (g) ⟶ 2NH (g) 2 2 3 This equation shows ammonia molecules are produced from hydrogen molecules in a 2:3 ratio, and stoichiometric factors may be derived using any amount (number) unit:

PDF page 207: A balanced chemical equation provides a great deal of information in a very succinct format. Chemical formulas provide the identities of the reactants and products involved in the chemical change, allowing classification of the reaction. Coefficients provide the relative numbers of these chemical species, allowing a quantitative assessment of the relationships between the amounts of substances consumed and produced by the reaction. These quantitative relationships are known as the reaction’s stoichiometry, a term derived from the Greek words stoicheion (meaning “element”) and metron (meaning “measure”). In this module, the use of balanced chemical equations for various stoichiometric applications is explored. The general approach to using stoichiometric relationships is similar in concept to the way people go about many common activities. Food preparation, for example, offers an appropriate comparison. A recipe for making eight 3 pancakes calls for 1 cup pancake mix, cup milk, and one egg. The “equation” representing the preparation of 4 pancakes per this recipe is 3 1 cup mix + cup milk + 1 egg ⟶ 8 pancakes 4 If two dozen pancakes are needed for a big family breakfast, the ingredient amounts must be increased proportionally according to the amounts given in the recipe. For example, the number of eggs required to make 24 pancakes is 1 egg 24 pancakes × = 3 eggs 8 pancakes Balanced chemical equations are used in much the same fashion to determine the amount of one reactant required to react with a given amount of another reactant, or to yield a given amount of product, and so forth. The coefficients in the balanced equation are used to derive stoichiometric factors that permit computation of the desired quantity. To illustrate this idea, consider the production of ammonia by reaction of hydrogen and nitrogen: N (g) + 3H (g) ⟶ 2NH (g) 2 2 3 This equation shows ammonia molecules are produced from hydrogen molecules in a 2:3 ratio, and stoichiometric factors may be derived using any amount (number) unit:

PDF page 208: mol I = 0.429 mol Al ×

PDF page 208: 2 2 mol Al = 0.644 mol I 2

PDF page 208: Check Your Learning How many moles of Ca(OH)2 are required to react with 1.36 mol of H3PO4 to produce Ca3(PO4)2 according to the equation 3Ca(OH) + 2H PO ⟶ Ca (PO ) + 6H O? 2 3 4 3 4 2 2 Answer: 2.04 mol

PDF page 209: 23 3 mol CO 6.022 × 10 CO molecules 2 24 2 0.75 mol C H × ×

PDF page 209: = 1.4 × 10 CO molecules

PDF page 209: Solution The approach here is the same as for Example 4.8, though the absolute number of molecules is requested, not the number of moles of molecules. This will simply require use of the moles-to-numbers conversion factor, Avogadro’s number. The balanced equation shows that carbon dioxide is produced from propane in a 3:1 ratio: 3 mol CO 2 1 mol C H 3 8 Using this stoichiometric factor, the provided molar amount of propane, and Avogadro’s number,

PDF page 209: Answer: 4.8 × 10 NH3 molecules

PDF page 210: 1 mol Mg(OH) 40.0 g NaOH 2 mol NaOH 2 16 g Mg(OH) × × × = 22 g NaOH 2 58.3 g Mg(OH) 1 mol Mg(OH) mol NaOH 2 2

PDF page 210: Check Your Learning What mass of gallium oxide, Ga2O3, can be prepared from 29.0 g of gallium metal? The equation for the reaction is 4Ga + 3O ⟶ 2Ga O . 2 2 3 Answer: 39.0 g

PDF page 211: 2 3 2 Answer: 13.22 g

PDF page 209: These examples illustrate the ease with which the amounts of substances involved in a chemical reaction of known stoichiometry may be related. Directly measuring numbers of atoms and molecules is, however, not an easy task, and the practical application of stoichiometry requires that we use the more readily measured property of mass.

PDF page 211: These examples illustrate just a few instances of reaction stoichiometry calculations. Numerous variations on the beginning and ending computational steps are possible depending upon what particular quantities are provided and sought (volumes, solution concentrations, and so forth). Regardless of the details, all these calculations share a common essential component: the use of stoichiometric factors derived from balanced chemical equations. Figure 4.11 provides a general outline of the various computational steps associated with many reaction stoichiometry calculations.