Ch 9. Stoichiometry. The recipe of chemistry

Transcription

1 Ch 9 Stoichiometry The recipe of chemistry

2 Warm up Analogy Suppose you are preparing a cake. Each Cake (Ck) requires 1.0 cake mix (Cm), 0.5 cup of oil (Oi), 1.0 cup of water (Wa) and 2.0 eggs (Eg). 1. Write the balanced equation for making cake: à cake mix cups oil cup water + 2 eggs à 1.0 cake 2. If you have 2 cake mixes, 2 cups oil, 3 cups water, 4 eggs, how many cakes can you make, what and how much is left over? 2

3 1.0 cake mix cups oil cup water + 2 eggs à 1.0 cake Calculating Cakes Calculate the number of cakes (Ck) that can be made from 12 cake mixes (Cm) 12Cm x 1 Ck = 12 Ck 1 Cm Calculate the number of cakes (Ck) that can be made from 10.0 cups of oil (Oi) 10.0 Oi x 1 Ck = 20 Ck 0.5Oi If you need to make 29 cakes (Ck), how many eggs (Eg) do you need? 29 Ck x 2 Eg = 58 Eg 1 Ck

4 Stoichiometry: the calculation of quantities in chemical reactions Equations are a chemist s recipe. Eqs tell chemists what amounts of reactants to mix and what amounts of products to expect. When you know the quantity of onesubstance in a rxn, you can calculate the quantity of any other substance consumed or created in the rxn.

5 Why should you care? Nearly everything we use is manufactured from chemicals. Soaps, shampoos, conditioners, CD s, cosmetics, medications, clothes. u For a manufacturer to make a profit the chemical processes carried out in industry must be economical u A balanced equation is needed and used so chemicals are not wasted when making products

6 Reading Chemical Equations How would you read: N 2 (g) + H 2 (g) à NH 3 (g) Balance and read: N 2 (g) + 3H 2 (g) à 2NH 3 (g) Coefficients can represent different possible units Atoms/molecules Moles Mass in grams Mass of reactants equals mass of products Law of Conservation of mass Liters (if compound is a gas at STP)

7 N 2 + 3H 2 2NH 3 1 mol N mol N 2 2 mol NH g N (2.0 g H 2 ) 2 (17.0 g NH 3 ) 22.4 L 34.0 g reactants L L 34.0 g products 22.4 L N L H L NH 3 L L L

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9 MOLE ratios: What are the possible mole ratios in: N 2 (g) + 3H 2 (g) à 2NH 3 (g) 1 mole of N 2 reacts with 3 moles of H 2 to produce 2 moles of NH 3. Possible mole ratios for this formula: 1N 2 1N 2 3H 2 3H 2 2NH 3 2NH 3 Reaction to form ammonia in this 1:3:2 ratio. Mole ratios are CONVERSION FACTORS! Once you have the ratios, you can perform calcs. (a.k.a. STOICHIOMETRY)

10 Conversion of Quan66es in Moles Amount of given (mol) Mole ra6o: from balanced equa6on X Mole unknown = Mole given Amount of unkown (mol) Pg 305 Ex: How many moles of water are produced from 5.80 moles of oxygen gas? O 2 + H 2 à H 2 O 1. Write equa6on 2. Balance! 3. Set up conversion factor O 2 + 2H 2 à 2H 2 O 5.80mole O 2 x 11.6 moles water 2 mol H 2 O 1 mol O 2

11 N 2 (g) + 3H 2 (g) à 2NH 3 (g) 1. How many moles of ammonia are produced from 0.60 moles of N 2? (1.2 mol NH 3 ) 2. How many moles of H 2 are needed to react with 0.43 moles of N 2 gas? (1.3 mol H 2 ) 3. How many moles of H 2 are needed to produce 1.98 moles of ammonia (NH 3 )? (2.97 mol H 2 )

12 Amount of given (mol) Mole ra6o: from balanced equa6on X Mole unknown = Mole given Amount of unkown (mol) 4. Ammonia, NH 3 is a widely used fer6lizer and used in household cleaners. How many moles of ammonia are produced when 6 mol of H gas react with excess nitrogen gas? 4 mol NH 3 5. The decomposi6on of potassium chlorate, KClO 3 into potassium chloride and oxygen gas is used as a source of oxygen in the lab. How many moles of potassium chlorate are needed to produce 15 mol of oxygen gas? 1. Write equa6on 2. Balance! 3. Set up conversion factor 10 mol KClO 3

13 Ch 9.1 Historical Chemistry: pg 303, #1-2

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15 Sn + 2HF à SnF 2 + H 2 1. How many moles of SnF 2 will be produced by 12.5 moles of HF? 2. How many moles HF are needed to produce 6.85 moles of SnF 2?

16 Calculating using MASS quantities No lab balance measures moles directly, instead grams is a more practical unit. To calculate grams: 1. convert to moles first, then grams Using our same example, you can calculate how many grams of each compound: N 2 (g) + 3H 2 (g) à 2NH 3 (g) REMEMBER: when you use a gram/mole conversion factor: 1 mol = molar mass 1 mol 2 mol NH 3.00 g N 2 x x 3 x 28g 1 mol N 2 17 g 1 mol

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18 Conversion of amount in Moles & Mass Par>cle A Mass A Volume A 6.022x x10 23 Molar Mass Mole Mole Mole Molar Mass A Ratio B 22.4 L 22.4 L Par>cle B Mass B Volume B Ex 1: What mass, in grams, of glucose is produced when 3.00 mol of water reacts with excess carbon dioxide to produce glucose and oxygen? 1. Write equa6on 2. Balance! 3. Set up conversa6on factor 6CO 2 + 6H 2 O à C 6 H 12 O 6 + 6O mol x 1 mol glucose 180.2g x 6 mol water 1 mole 90.1g glucose

19 examples Par>cle A Mass A Volume A 6.022x x10 23 Molar Mass Mole Mole Mole Molar Mass A Ratio B 22.4 L 22.4 L Par>cle B Mass B Volume B 2. What mass of carbon dioxide is needed to react with 3.00 mol water? 6CO 2 + 6H 2 O à C 6 H 12 O 6 + 6O 2 3. How many moles of H 2 O are formed from a reac6on using 824g NH 3 is the reac6on: NH 3 + O 2 à NO + H 2 O (unbalanced) 4NH 3 + 5O 2 à 4NO + 6H 2 O 132g CO mol H 2 O

20 Sn + 2HF à SnF 2 + H 2 Warm up 1. How many moles of SnF 2 will be produced by 12.5 moles of HF? 2. How many moles HF are needed to produce 685g of SnF 2? 3. How many moles of Sn are needed to produce 2.50L of H 2 Par>cle A Mass A Volume A 6.022x x10 23 Molar Mass Mole Mole Mole Molar Mass A Ratio B 22.4 L 22.4 L Par>cle B Mass B Volume B

21 Conversion of amount: Mass to Mass Par>cle A Mass A Volume A 6.022x x10 23 Molar Mass Mole Mole Mole Molar Mass A Ratio B 22.4 L 22.4 L Ex 1: How many grams of SnF 2 are produced from the reac6on of 30.00g HF with Sn. Sn (s) + 2HF (g) à SnF 2(s) +H 2(g) Par>cle B Mass B Volume B 1 mol HF 30.00g HF x 20.0 g HF x 1 mol SnF 2 x 2 mol HF 156.7g SnF 2 1 mol SnF g SnF 2 2. How many grams of NH 4 NO 3 are required to produce 33.0g N 2 O? (the laughing gas needed for an anesthe6c in den6stry) 60.0g NH 4 NO 3 NH 4 NO 3(s) à N 2 O (g) + 2H 2 O (l) 3. How many molecules of oxygen gas are produced when 29.2 g of water is decomposed? (4.88 * molecules of O 2 )

22 More Problems to Practice 1. Carbon dioxide is produced from the synthesis of oxygen gas with carbon monoxide. Write and balance this chemical equation and then tell how many liters of oxygen gas are required to burn 3.86 liters of carbon monoxide. Assume STP. (1.93 L O 2 ) 2. How many grams of NH 4 NO 3 are required to produce 33.0g N 2 O? (the laughing gas needed for an anesthe6c in den6stry) NH 4 NO 3(s) à N 2 O (g) + 2H 2 O 60.0g NH (l) 4 NO 3 3. How much water in grams is produced in this reac6on? 27.0g H 2 O

23 Stoichiometry Practice Answer in classwork section of notebook: N 2 (g) + 3H 2 (g) à 2NH 3 (g) 1. Calculate the number of grams of ammonia produced by the reaction of 5.40 g of H 2 with N 2. (30.6 g NH 3 ) 2. Calculate the number of liters of N 2 needed in order to react with 0.78 moles of H 2. (5.8 L N 2 ) 3. Calculate the grams of N 2 needed in order to produce 9.23 x molecules of NH 3. (21.5 g N 2 ) Par>cle A Mass A Volume A 6.022x x10 23 Molar Mass Mole Mole Mole Molar Mass A Ratio B 22.4 L 22.4 L Par>cle B Mass B Volume B

24 Stoichiometry Practice Answer in classwork section of notebook: N 2 (g) + 3H 2 (g) à 2NH 3 (g) 1. Calculate the number of grams of ammonia produced by the reaction of 5.40 g of H 2 with N 2. (30.6 g NH 3 ) 2. Calculate the number of liters of N 2 needed in order to react with 0.78 moles of H 2. (5.82 L N 2 ) 3. Calculate the grams of N 2 needed in order to produce 9.23 x molecules of NH 3. (21.5 g N 2 ) Pg 311 Section Review #4 (assume silver has +1 charge) pg 313 Practice #1 Pg 318 Section Review #1-3 (next class)

25 MOLE-MOLE RATIO You will ALWAYS use the new MOLE-MOLE ratio step to get you from where you are to where you are are going. Par>cle A Mass A Volume A 6.022x x10 23 Molar Mass Mole Mole Mole Molar Mass A Ratio B 22.4 L 22.4 L Par>cle B Mass B Volume B

26 More Problems to Practice Carbon dioxide is produced from the synthesis of oxygen gas with carbon monoxide. Write and balance this chemical equation and then tell how many liters of oxygen gas are required to burn 3.86 liters of carbon monoxide. Assume STP. (1.93 L O 2 )

27 Problems to Practice Aluminum reacts with oxygen to produce Aluminum Oxide. How many moles of aluminum are needed to form 3.7 moles of Aluminum Oxide? Write the balanced equation and solve. (7.4 mol Al)

28 More Problems to Practice How many molecules of oxygen gas are produced when 29.2 g of water is decomposed? The balanced chemical equation is given for you. Use your new mole map to solve. 2H 2 O electricityà 2H 2 + O 2 (4.88 * molecules of O 2 ) How many molecules of oxygen are produced by the decomposition of 6.54 g of Potassium Chlorate? The balanced chemical equation is given for you. Use your new mole map to solve. 2KClO 3 à 2KCl + 3O 2 (4.82 * molecules of O 2 )

29 Even More Problems Sodium hydroxide reacts with Sulfuric acid to produce water and Sodium Sulfate. Calculate the amount of water (in grams) that would be produced from g of the acid. (15.0 g H 2 O) In a combustion reaction, C 2 H 4 reacts with oxygen to produce H 2 O and CO 2 in the following reaction. Balance it and then determine the amount of oxygen (in grams) that is consumed if 2.69g of water is produced. C 2 H 4 + O 2 à CO 2 + H 2 O (7.17 g O 2 )

30 Mole to mass Amount of given (mol) Mole ra6o: (balanced equa6on) Molar mas: (periodic table) Mole unknown molar mass unknown(g) Mole given 1 mole unkown X x = mass of unkown (g) Mass of given (g) Molar mas: (periodic table) 1 mole given mol unknown molar mass mol given given (g) Mole ra6o: (balanced equa6on) X x = Amount unkown (mol)

31 Mass of given (g) X x X = 1 mole given mol unknown mole mass molar mass mol given 1 mol given (g) unknown mass of unknown (g)

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33 Warm up 1. Carbon dioxide is produced from the synthesis of oxygen gas with carbon monoxide. Write and balance this chemical equation and then tell how many liters of oxygen gas are required to burn 3.86 liters of carbon monoxide. Assume STP. (1.93 L O 2 ) Par>cle A 6.022x x10 23 Par>cle B Mass A Molar Mass Mole A Mole Ratio Mole B Molar Mass Mass B Volume A 22.4 L 22.4 L Volume B

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35 How many sandwiches, how much excess?

36 Limiting Reagent (Ch. 9.3) Limiting reagent: reactant that determines the amount of product that can be produced. It limited Excess reagent: reactant that is not used up in the reaction - there is more available than needed Steps to determine LR Calculate theoretical yield (g or mol) Determine limited reagent Use the original actual yield of the limiting reactant to calculate product produced (in moles or grams)

37 Problems to Practice Ex 1. Given the following balanced equation, determine which is the LR if 2.70 moles of C 2 H 4 is reacted with 6.30 moles of O 2. How much water is made? C 2 H 4 + 3O 2 à 2H 2 O + 2CO 2 (O 2 is LR) 2.70 mol C 2 H 4 x 2 mole H 2 O = 5.4 mol H 2 O 1 mole C 2 H mol O 2 x 2 mole H 2 O = 4.20 mol O 2 3 mole O 2 Less= limi6ng reagent=o 2 2. Using the info gathered from above, calculate the GRAMS of water that will be produced. 4.20mol x 18g/mol = 75.6 g H 2 O

38 Warm Up #2 (March) 2H 2 + O 2 2H 2 + O 2 è 2Η 2 Ο è 2Η 2 Ο 3 O 2 & 7 H 2 1. How many mole of hydrogen molecules are needed to reac6on with one mole of oxygen molecules? 2. How many water molecules are produced if one mole of oxygen molecules completely reacts? 3. How many water molecules could form in container Q? 4. Which reactant (oxygen or hydrogen) limited the produc6on of water in container Q? 5. Which reactant (oxygen or hydrogen) was present in excess and remained aber the produc6on of water was complete??

39 Limi6ng Reactant More Problems to Practice 3. Identify the LR when 6.00 g HCl reacts with 5.00 g Mg in the following reaction: Mg + 2HCl à MgCl 2 + H 2 (HCl is LR) 4. Using the info gathered from above, calculate the GRAMS of hydrogen gas that will be produced. How much of the excess reactant is left? (0.164 g H 2 )

40 Flask Volume ace>c acid (ml) Demo 25ml 25ml 25ml 25ml 25ml 25ml Sodium bicarbona te (g) 0.50g 1.00g 1.50g 2.00g 2.50g 3.00g Which system will produce the most CO 2 product?

41 Theoretical yield vs Actual yield: Ch 9.3 The difference in the op6mal, expected outcome and the actual tested outcome Experimenta6on is not perfect Not all reactant are react so some may be leb over Condi6ons may not be perfect for a full reac6on Actual: get in an experiment Theore>cal: maximum produced in perfect theore6cal condi6ons

42 Percent Yield % yield = actual yield x 100% theoretical yield measure of the efficiency of a reaction carried out in lab. Actual yield would be given in problem or determined from actually performing the lab. Theoretical yield can be calculated using the Limiting Reagent.

43 Percent Yield: Problem to Practice If 15.0 g of nitrogen gas reacts with 15.0 g of hydrogen gas, 10.5 g of ammonia (NH 3 ) is produced. Calculate the percent yield. N 2 yields 1.07 mol NH 2 H 2 yields 5.0mol NH 2 Limiting reactant: N 2 (theoretical yield: 18.2 g NH 3 ) (percent yield: 57.7%) 1. Balance chemical equa>on 2. Find limi>ng reactant 3. Calculate theore>cal yield 4. Find percent yield % yield = actual yield x 100 theoretical yield

44 Stoichiometry Practice Answer in classwork section of notebook: N 2 (g) + 3H 2 (g) à 2NH 3 (g) 1. Calculate the number of grams of ammonia produced by the reaction of 5.40 g of H 2 with N 2. (30.6 g NH 3 ) 2. Calculate the number of liters of N 2 needed in order to react with 0.78 moles of H 2. (5.82 L N 2 ) 3. Calculate the grams of N 2 needed in order to produce 9.23 x molecules of NH 3. (21.5 g N 2 ) Pg 311 Section Review #4 (assume silver has +1 charge) pg 313 Practice #1 Pg 318 Section Review #1-3

45 Warm up 15.0 g Mg is used in the following reaction: Mg + 2HCl à MgCl 2 + H 2 1. Calculate the theore6cal yield, in grams, of hydrogen gas. 1.23g H 2 2. Calculate the percent yield if 1.15 grams of H 2 are produced. 93.5% Then con6nue Stoichiometry Prac6ce- classwork if not finished

46 True or False #1 The limi6ng reactant will be the reactant that produces the most product. (F)

47 True or False #2 To calculate percent yield, you must be given the actual yield and have to use the balanced equa6on to calculate the theore6cal yield (T)

48 True or False #3 Actual yield is 3.00g and theore6cal yield is 4.00g. What is the %yield? (75%)

49 I m not sure I ve got this.

50 More Review? Pg 325 Standardized Test Prep #1-12

51 Par>cle A 6.022x x10 23 Par>cle B Mass A Molar Mass Mole A Mole Ratio Mole B Molar Mass Mass B Volume A 22.4 L 22.4 L Volume B

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53 Common Core Standards HS- PS1-7. Use mathema>cal representa>ons to support the claim that atoms, and therefore mass, are conserved during a chemical reac>on. HS- PS1-6. Refine the design of a chemical system by specifying a change in condi>ons that would produce increased amounts of products at equilibrium. HS- PS1-5. Apply scien>fic principles and evidence to provide an explana>on about the effects of changing the temperature or concentra>on of the reac>ng par>cles on the rate at which a reac>on occurs. HS- PS1-3. Plan and conduct an inves>ga>on to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between par>cles.

54 Common Core Standards HS- PS1-7. Use mathema>cal representa>ons to support the claim that atoms, and therefore mass, are conserved during a chemical reac>on. CA State Standards D2. Inves1gate quan1ta1ve rela1onships in chemical reac1ons, and solve related problems; D3. Demonstrate an understanding of the mole concept and its significance to the quan1ta1ve analysis of chemical reac1ons.

55 Common Core Standards HS- PS1-6. Refine the design of a chemical system by specifying a change in condi>ons that would produce increased amounts of products at equilibrium.

56 Common Core Standards HS- PS1-5. Apply scien>fic principles and evidence to provide an explana>on about the effects of changing the temperature or concentra>on of the reac>ng par>cles on the rate at which a reac>on occurs.

57 Common Core Standards HS- PS1-3. Plan and conduct an inves>ga>on to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between par>cles.