How do you figure out how much starting material you need to make a finished product?

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1 CHEMISTRY & YOU Chapter 1 Stoichiometry 1.1 The Arithmetic of Equations 1. Chemical Calculations 1.3 imitin Reaent and Percent Yield How do you fiure out how much startin material you need to make a finished product? When makin bikes, you need parts like wheels, handlebars, pedals, and frames. 1 Usin Equations Usin Equations How do chemists use balanced chemical equations? Usin Equations Everyday Equations Travel Time Tricycle company produces 640 tricycles each week. How can you determine the number of parts they need per week? Usin Equations Everyday Equations Travel Time Tricycle company produces 640 tricycles each week. How can you determine the number of parts they need per week? The major components are the frame (F), the seat (S), the wheels (W), the handlebars (H), and the pedals (P). Usin Equations Everyday Equations Travel Time Tricycle company produces 640 tricycles each week. How can you determine the number of parts they need per week? The finished tricycle, your product, has a formula of FSW 3 HP

2 Usin Equations Sample Problem 1.1 Everyday Equations Travel Time Tricycle company produces 640 tricycles each week. How can you determine the number of parts they need per week? The balanced equation for makin a sinle tricycle is: F + S + 3W + H + P FSW 3 HP Usin a Balanced Equation as a Recipe In a five-day workweek, Travel Time is scheduled to make 640 tricycles. How many wheels should be in the plant on Monday mornin to make these tricycles? Sample Problem 1.1 Sample Problem Analyze ist the knowns and the unknown. Use the balanced equation to identify a conversion factor that will allow you to calculate the unknown. The conversion you need to make is from tricycles (FSW 3 HP ) to wheels (W). KNOWNS number of tricycles = 640 tricycles = 640 FSW 3 HP F + S + 3W + H + P FSW 3 HP Calculate Solve for the unknown. Identify a conversion factor that relates wheels to tricycles. You can write the two conversion factors relatin wheels to tricycles. 3 W 1 FSW 3 HP and 1FSW 3 HP 3 W 9 UNKNOWN number of wheels =? wheels 10 Sample Problem 1.1 Sample Problem 1.1 Calculate Solve for the unknown. The desired unit is W; so use the conversion factor on the left. Multiply the number of tricycles by the conversion factor. 3 W 1 FSW 3 HP 1 FSW 3 HP and 3 W 3 W 640 FSW 3 HP 1 FSW = 190 W 3 HP When usin conversion factors, remember to cross out like units when they are in both the numerator and denominator. This will help you check that you are usin the correct conversion factor. 3 Evaluate Does the result make sense? If three wheels are required for each tricycle and more than 600 tricycles are bein made, then a number of wheels in excess of 1800 is a loical answer. The unit of the known (FSW 3 HP ) cancels. The answer has the correct unit (W). 11 1

3 Usin Equations Usin Equations Balanced Chemical Equations Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or how much product will be formed in a reaction. Balanced Chemical Equations Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or how much product will be formed in a reaction. When you know the quantity of one substance in a reaction, you can calculate the quantity of any other substance consumed or created in the reaction Usin Equations Balanced Chemical Equations The calculations of quantities in chemical reactions is a subject of chemistry called stoichiometry. Usin Equations Balanced Chemical Equations The calculations of quantities in chemical reactions is a subject of chemistry called stoichiometry. For chemists, stoichiometry is a form of bookkeepin. It allows chemists to tally the amounts of reactants and products usin ratios of es or representative particles Cayla is usin a recipe to make chocolate chip cookies. She wants to double the number of cookies that the recipe will make. The oriinal recipe calls for cups of chocolate chips. How many cups of chips should Cayla use for a double recipe? Cayla is usin a recipe to make chocolate chip cookies. She wants to double the number of cookies that the recipe will make. The oriinal recipe calls for cups of chocolate chips. How many cups of chips should Cayla use for a double recipe? A. cups C. 1 cup B. 4 cups D. 8 cups A. cups C. 1 cup B. 4 cups D. 8 cups

4 Chemical Equations Chemical Equations Chemical Equations In terms of what quantities can you interpret a balanced chemical equation? Ammonia is produced industrially by the reaction of nitroen with hydroen. N () + 3H () NH 3 () The balanced chemical equation tells you the relative amounts of reactants and product in the reaction Chemical Equations CHEMISTRY & YOU Ammonia is produced industrially by the reaction of nitroen with hydroen. How can you determine the amount of each reactant you need to make a product? N () + 3H () NH 3 () The balanced chemical equation tells you the relative amounts of reactants and product in the reaction. Your interpretation of the equation depends on how you quantify the reactants and products. 1 CHEMISTRY & YOU Chemical Equations How can you determine the amount of each reactant you need to make a product? A recipe or an equation, such as a balanced chemical equation, is used to determine how much startin material is needed or how much product will be made. A balanced chemical equation can be interpreted in terms of different quantities, includin numbers of atoms, ecules, or es; mass; and volume

5 Chemical Equations Chemical Equations Number of Atoms At the atomic level, a balanced equation indicates the number and types of atoms that are rearraned to make the product or products. In the synthesis of ammonia, the reactants are composed of two atoms of nitroen and six atoms of hydroen. atoms N + 6 atoms H atoms N and 6 atoms H Number of Molecules Nitroen and hydroen will always react to form ammonia in a 1:3: ratio of ecules. It is not practical to count very small numbers of ecules and allow them to react. You could take Avoadro s number ( ecules) of nitroen ecules and make them react with three times Avoadro s number of hydroen ecules ( ) + 3 ( ) 3 ( ) ecules N ecules N ecules NH Chemical Equations Chemical Equations Moles Since a balanced chemical equation tells you the number of representative particles, it also tells you the number of es. In the synthesis of ammonia, one e of nitroen ecules reacts with three es of hydroen ecules to form two es of ammonia ecules. 1 N + 3 H NH 3 Mass A balanced chemical equation obeys the law of conservation of mass. Mass can be neither created nor destroyed in an ordinary chemical or physical process. The total mass of the atoms in a reaction does not chane. 8 N + (3 H ) ( 17 NH 3 ) N + 6 H 34 NH 3 Chemical Equations Sample Problem 1. Volume If you assume standard temperature and pressure, the balanced chemical equation also tells you about the volumes of ases. 1 of any as at STP occupies a volume of.4..4 N + (3.4 H ) (.4 NH 3 ).4 N H 44.8 NH 3 Interpretin a Balanced Chemical Equation Hydroen sulfide, which smells like rotten es, is found in volcanic ases. The balanced equation for the burnin of hydroen sulfide is: H S() + 3O () SO () + H O() Interpret this equation in terms of a. numbers of representative particles and es. b. masses of reactants and produces

6 Sample Problem 1. Sample Problem 1. 1 Analyze Identify the relevant concepts. The coefficients in the balanced equation ive the relative number of representative particles and es of reactants and products. A balanced chemical equation obeys the law of conservation of mass. Solve Apply concepts to this situation. Use the coefficients in the balanced equation to identify the number of representative particles and es. ecules H S + 3 ecules O ecules SO + ecules H O H S + 3 O SO + H O Remember that atoms and ecules are both representative particles. In this equation, all the reactants and products are ecules; so all the representative particles are ecules Sample Problem 1. Sample Problem 1. Solve Apply concepts to this situation. Use the periodic table to calculate the ar mass of each reactant and product. 1 H S = 34.1 H S 1 O = 3.0 O 1 SO = 64.1 / SO 1 H O = 18.0 / H O Solve Apply concepts to this situation. Multiply the number of es of each reactant and product by its ar mass. H S + 3 O SO + H O ( 34.1 ) + (3 3.0 ) ( 64.1 ) + ( 18.0 ) Sample Problem 1. Solve Apply concepts to this situation. Multiply the number of es of each reactant and product by its ar mass. H S + 3 O SO + H O ( 34.1 ) + (3 3.0 ) ( 64.1 ) + ( 18.0 ) 68. H S O 18. SO H O 164. = 164. Chemical Equations 36 The table below summarizes the information derived from the balanced chemical equation for the formation of ammonia. N () + H () NH 3 () + atoms N + 6 atoms H atoms N and 6 atoms H 1 ecule N + 3 ecules H ecules NH 3 10 ecules N + 30 ecules H 0 ecules NH 3 ( ) ecules N ecules H Assume STP 1 N + 3 H NH 3 3 N + 3 H 17 NH N +.4 ( ) ( 3 ecules NH ) 34 reactants 34 products H 44.8 NH 3 6

7 Chemical Equations Mass and atoms are conserved in every chemical reaction. Molecules, formula units, es, and volumes are not necessarily conserved althouh they may be. Interpret the followin equation in terms of volumes of as at STP. H () + NO() N () + H O() Key Concepts 39 Interpret the followin equation in terms of volumes of as at STP. H () + NO() N () + H O() 44.8 H () NO().4 N () H O() 40 A balanced chemical equation provides the same kind of quantitative information that a recipe does. Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction. A balanced chemical equation can be interpreted in terms of different quantities, includin numbers of atoms, ecules, or es; mass; and volume. Mass and atoms are conserved in every chemical reaction. Glossary Terms BIG IDEA stoichiometry: that portion of chemistry dealin with numerical relationships in chemical reactions; the calculation of quantities of substances involved in chemical equations The Mole and Quantifyin Matter Balanced chemical equations are the basis for stoichiometric calculations. The coefficients of a balanced equation indicate the number of particles, e, or volumes of as in the reaction

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