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Starter S-125 1.2 moles NaC 2 H 3 O 2 are used in a reaction. How many grams is that?

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Stoichiometry Chapter 12

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12.1 The Arithmetic of Equations Chapter 12

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The basis for solving stoichiometry problems is a balanced chemical reaction A balanced reaction is used to calculate How much reactant is needed How much product is produced 12.1 The Arithmetic of Equations

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Stoichiometry – the calculation of quantities This reaction produces Ammonia which is used in fertilizers Balanced reactions are usually used to calculate grams of product or reactant 12.1 The Arithmetic of Equations

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Analysis of the reaction Atoms – 2 atoms of nitrogen combine with 6 atoms of hydrogen – product is 2 nitrogen and 6 hydrogen Molecules – 1 molecule of nitrogen gas combines with 3 molecules of hydrogen gas to produce 2 molecules of ammonia 12.1 The Arithmetic of Equations

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Analysis of the reaction Most useful Moles – 1 mole of nitrogen gas reacts with 3 moles of hydrogen gas to produce 2 moles of ammonia 12.1 The Arithmetic of Equations

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Analysis of the reaction Mass is always conserved in a chemical reaction 12.1 The Arithmetic of Equations

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Analysis of the reaction The key moles can be converted to grams grams can be converted to moles Volume – remember that one mole of gas at STP is 22.4L 12.1 The Arithmetic of Equations

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Analysis of the reaction The key moles can be converted to grams grams can be converted to moles Volume – remember that one mole of gas at STP is 22.4L 12.1 The Arithmetic of Equations

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Analysis of the reaction So if we start with 50g of N 2, how many moles do we have How many moles of NH 3 would be produced? For every 1 mole of N 2, 2 moles of NH 3 12.1 The Arithmetic of Equations

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Analysis of the reaction How many grams of ammonia are produced 12.1 The Arithmetic of Equations

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Starter S-126 A. Balance the following reactions H 2 SO 4 + KOH K 2 SO 4 + H 2 O B.What is the molar mass of the sulfuric acid. C.If 20.0g of sulfuric acid is used, how many moles is that? D.How many moles of water would be produced?

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12.2 Chemical Calculations Chapter 12

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12.2 Chemical Calculations Mole Ratios Come from balanced chemical reactions Conversion factors derived from the coefficients in the balanced reactions 12.2 Chemical Calculations

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Mole-Mole Calculations It is possible to convert from one quantity in a balanced reaction to another using mole ratios For example – if 3.7 moles of sulfur dioxide is produced, how many moles of oxygen were used? 12.2 Chemical Calculations

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Mass-Mass Calculations Three steps 1.Convert given mass values into mole values. 2.Use a mole ratio to convert to the moles that the question requests 3.Convert this mole quantity to a mass value 12.2 Chemical Calculations

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Mass-Mass Calculations How many grams of Oxygen are needed to produce 30.0g of Sulfur Dioxide? 12.2 Chemical Calculations

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Volume-Mass Calculations Same steps, but volume is converted to moles, or moles to volume Example: If 4.0L of nitrogen monoxide reacts, how many grams of oxygen are used? 12.2 Chemical Calculations

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Starter S-127 A. Balance the following reactions Al(NO 3 ) 3 + Na 2 SO 4 Al 2 (SO 4 ) 3 +NaNO 3 B. If 50.0g of Aluminum Nitrate reacts, how many grams of Aluminum Sulfate are produced?

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12.3 Limiting Reagent and Percent Yield Chapter 12

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Limiting Reagent – the reactant that runs out first Amounts of both reactants are given Example: 80.0g Copper, 25.0g Sulfur 1.Calculate how many moles would each reactant produce Copper 12.3 Limiting Reagent and Percent Yield

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Limiting Reagent – the reactant that runs out first Amounts of both reactants are given Example: 80.0g Copper, 25.0g Sulfur 1.Calculate how many moles would each reactant produce Sulfur 12.3 Limiting Reagent and Percent Yield

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Limiting Reagent – the reactant that runs out first From the reactions Copper would produce 0.630 mol Cu 2 S Sulfur would produce 0.780 mol Cu 2 S That means copper will run out first – it is the limiting reagent Sulfur would be the excess reagent 12.3 Limiting Reagent and Percent Yield

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One for you now 1.Balance the reaction 2.If 75.6g C 2 H 4 reacts with 100.8g O 2 – what is the limiting reagent? Oxygen 3.How many moles of water are produced? 2.10 mol H 2 O 4.How many grams of water are produced? 12.3 Limiting Reagent and Percent Yield

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Starter S-132 A. Balance the following reactions SiO 2 + C SiC + CO B. 35 grams of silicon dioxide reacts with 10.0g of Carbon, how much carbon monoxide is formed?

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Reactions rarely produce as much product as is predicted -reactants can be impure -reactions may not go to completion -may compete with smaller “side” reactions In some reactions as little as 60% yield is considered a good result 12.3 Limiting Reagent and Percent Yield

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Yield – how much product is produced Theoretical Yield – the value calculated using stoichiometry Actual Yield – the amount of product that actually forms 12.3 Limiting Reagent and Percent Yield

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Percent Yield – a ratio of actual to theoretical yield This number must be 100% or less In lab the actual yield is the result you get On a test, it will be a number that is given to you The theoretical yield is calculated using limiting reactants 12.3 Limiting Reagent and Percent Yield

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Example: What is the theoretical yield of Calcium Oxide if 24.8g of Calcium Carbonate decomposes in the following reaction. Balanced 12.3 Limiting Reagent and Percent Yield

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Example: What is the percent yield if actual yield is 9.6g? 12.3 Limiting Reagent and Percent Yield

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Example: What is the theoretical yield if 15.0g of nitrogen reacts with 15.0g of hydrogen in the following reaction? Balance 12.3 Limiting Reagent and Percent Yield

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Example: If the actual yield is 10.5g of NH 3 what is the percent yield? 12.3 Limiting Reagent and Percent Yield

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