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Stoichiometry

1. Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions. Stoichiometry. STOY-KEE-AHM-EH-TREE. 2. GOALS. 1. Demonstrate the conceptual principle of limiting reactants. 2. Explain the role of equilibrium in chemical reactions.

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Stoichiometry

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  1. 1 Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions. Stoichiometry STOY-KEE-AHM-EH-TREE

  2. 2 GOALS 1. Demonstrate the conceptual principle of limiting reactants. 2. Explain the role of equilibrium in chemical reactions 3. Identify and solve different types of stoichiometry problems, specifically relating mass to moles and mass to mass. The Mole Song- A Review

  3. Before we start…let’s review….. 3 Moles & Molar Mass Review • 1 mole is _______ atoms/molecules • How many atoms are in 1.5 moles of neon? • Calculate the number of grams in 3.25-mol of AgNO3 • How many moles are there in 250.0 grams of sodium phosphate (Na3PO4)? • How many grams are in 5.6 x 1023 atoms of Zinc?

  4. 4 Practice with a Friend  • What is the mass of 7.50 moles of sulfur dioxide (SO2)? • How many moles are there in 21.4 grams of nitrogen gas (N2)? • How many moles are there in 250.0 grams of sodium phosphate (Na3PO4)? • How many calcium atoms would be in a 100 gram sample of calcium metal? • Find the mass in grams of 7.5  1015 atoms of nickel.

  5. “amounts of substances that are involved in reactions” 5 Stoichiometry • Stoichiometry • is the calculation of relative quantities of reactants and products in chemical reactions • helps you figure out how much of a compound you will need, or maybe how much you started with. 2HCl + Ba(OH)2 2H2O + BaCl2 1 1 coefficients give MOLAR RATIOS What are some molar ratio we can write from this equation?

  6. “amounts of substances that are involved in reactions” 6 Stoichiometry What do we know from this equation? there is: one mole of CH4 for every two moles of H2O there is: one mole of CH4 for every one mole of CO2 there are: 2 molecules of O2 for every one molecule of CO2 there are even: four atoms of H in CH4 for every two atoms of O in 2H2O

  7. 7 Stoichiometry CH4 + 2O2 CO2 + 2H2O there is: one mole of CH4 for every two moles of H2O there are: 2 molecules of O2 for every one molecule of CO2 there are even: four atoms of Hin CH4 for every two atoms of Oin 2H2O How can we write these as conversion factors?

  8. 8 Stoichiometry Now you try: Write as many conversion factors as you can 1) C3H8 + 5O2 3CO2 + 4H2O What do we know from the balanced equation? • 1 molecule of propane for every 3 molecules of CO2 • 3 atoms of C in propane for 4 molecules of water • 9 atoms of hydrogen in propane for 8 atoms of hydrogen in water 2) Fe + S  FeS What do we know from the balanced equation? 1 atom  of Fe   +   1 atom  of S  ---->   1 molecule of FeS 10 atoms of Fe  + 10 atoms of S ----> 10 molecules of FeS 55.8 mg of Fe  +      32.1 mg S  ---->   87.9 mg  FeS 5.58 g of Fe     +      3.21 g of S ----> 8.79 g of FeS http://laude.cm.utexas.edu/courses/ch301/lecture/ln2rf07.pdf

  9. Our goal..To be able to determine amounts of products and reactants…moles and grams….for ANY chemical reaction. • Cutesy….but GOOD… video clip about mole conversions. • After this video, we will now have a class rule about all conversions…. • You must go through……… 2 CH3OH (l) + 3 O2 (g) --> 2 CO2 (g) + 4 H2O (l)

  10. 9 Mole to Mole 2KClO3 → 2KCl + 3O2 How many moles of oxygen are produced by the decomposition of 6.0 moles of potassium chlorate? • In the lab, you can’t work with single atoms or molecules. So, it is useful to be able to identify how many moles of one substance you need to make a certain amount of another substance. N2 + 3H2 → 2NH3 How many moles of hydrogen are needed to completely react with 2.0 moles of nitrogen?

  11. 10 Mole to Mole Practice • Carbon disulfide is an important industrial solvent. It is prepared by the reaction of carbon with sulfur dioxide: 5C(s) + 2SO2(g) ----> CS2(s) + 4CO(g) • How many moles of CS2 form when 6.3 mol of C reacts? • How many moles of carbon are needed to react with 7.24 moles of SO2?

  12. Mole to Mole Practice 11 Silver can be made according to the following equation: 2AgNO3+ Ca Ca(NO3)2 + 2Ag -If 35.3 moles of silver nitrate are reacted how many moles of silver are produced?

  13. 12 Mole to Mole Practice with a Friend Use the following equation to answer the questions below: 2 CH3OH (l) + 3 O2 (g) --> 2 CO2 (g) + 4 H2O (l) How many moles of water will be produced from the combustion of 0.27 moles of CH3OH? How many moles of O2 are needed to burn 2.56 moles of CH3OH? How many moles of CO2 are produced from the combustion of 5.25 moles of CH3OH? How many moles of water are produced when 3.25 moles of CO2 are formed? 0.54 mol H2O 3.84 mol O2 5.25 mol CO2 6.50 mol H2O

  14. Mole to Mole Practice with a Friend 13 When N2O5 is heated, it decomposes: 2N2O5(g) 4NO2(g) + O2(g) 5. How many moles of NO2 can be produced from 4.3 moles of N2O5? 4.3 mol N2O5 8.6 = moles NO2 6.How many moles of O2 can be produced from 4.3 moles of N2O5? 4.3 mol N2O5 = moles O2 2.2

  15. 14 Mass to Moles/ Moles to Mass 2 KClO3 ---> 2 KCl + 3 O2 • 1.50 mol of KClO3 decomposes. • How many grams of O2 will be produced? • (1.50 mol of KClO3/1) x (3 O2/2 mol of KClO3) x (32g / 1 mol O2) = 72 g 1.5 mol KCLO3 15.99g O2 1 Mol O2

  16. Mass to Moles/ Moles to Mass 15 2 KClO3 ---> 2 KCl + 3 O2 • If 80.0 grams of O2 was produced, how many moles of KClO3 decomposed? • We want to produce 2.75 mol of KCl. How many grams of KClO3 would be required? 337 g of KClO3 337 g of KClO3

  17. Mass to Moles/ Moles to Mass 16 Practice with a friend 2 H2 + O2 ---> 2 H2O • How many grams of H2O are produced when 2.50 moles of oxygen are used? 2) If 3.00 moles of H2O are produced, how many grams of oxygen must be consumed? 3)How many moles of Li required to make 46.4 g of Li3N? 90 g of H2O 48 g of O2 6 Li(s) + N2(g)  2 Li3N(s) 46.4 g Li3N x (1 mol Li3N/34.8 g Li3N) x (6 mol Li/2 mol Li3N) = 4.00 mol Li

  18. Mass to Moles/ Moles to Mass 17 _Pb(NO3)2+ _KI_PbI2+_KNO3 4. How many grams of Pb(NO3)2 are needed to react completely with 9.00 mol KI? 1490g Pb(NO3)2 _CH4 + _O2 _CO2+_H2O 5. How many moles of water will be produced when 8.5 g of CH4 react with oxygen? 0.81 mol O2 2N2O5(g)  4NO2(g) + O2(g) 6. How many moles of N2O5 were used if 210g of NO2 were produced?

  19. Mass to Moles/ Moles to Mass 18 7. How many grams of chlorine are required to react completely with 5.00 moles of sodium to produce sodium chloride? 2 Na + Cl2 2 NaCl 8. Calculate the number of moles of ethane (C2H6) needed to produce 10.0 g of water. 2 C2H6 + 7 O2 4 CO2 + 6 H20

  20. Std Dev Mass-Mass conversions video clip Mass to Mass 19 MgCl2 (aq) + 2 AgNO3 (aq)  2 AgCl (s) + Mg(NO3)2 (aq) How many grams of silver chloride could be produced by the complete reaction of 19.7 g of magnesium chloride with silver nitrate?  4 FeS2 + 11 O2 → 2 Fe2O3 + 8 SO2 If iron pyrite, FeS2, is not removed from coal, oxygen from the air will combine with both the iron and the sulfur as coal burns. If a furnace burns an amount of coal containing 125 g of FeS2, how many grams of SO2 (an air pollutant) is produced?

  21. 20 Mass TO Mass How many grams of water can I make from 25 grams of hydrogen gas and an excess of oxygen gas, using the reaction • 2 H2 + O22 H2O 225 grams of water

  22. 21 Mass to Mass Practice • How many grams of CO2 will be produced by the combustion of 15.0 g of propane? C3H8 (g) + 5 O2 (g) --> 3 CO2 (g) + 4 H2O (l) • How many grams of HCl are needed to react with 27.62 g of Fe2O3? Fe2O3 (s) + 6 HCl (g) --> 2 FeCl3 (s) + 3 H2O (g)

  23. 22 2N2O5(g)  4NO2(g) + O2(g) 3. How many grams of N2O5 are needed to produce 75.0 grams of O2? 4. Calculate how many grams of ammonia are produced when you react 2.00g of nitrogen with excess hydrogen. N2 + 3 H2  2 NH3

  24. 23 2Al(s) + 6HCl(aq)  2AlCl3(aq) + 3H2(g) 5. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? 6. During its combustion, ethane C2H6, combines with oxygen O2 to give carbon dioxide and water.  A sample of ethane was burned completely and the water that formed has a mass of 1.61 grams.  How many grams of ethane was in the sample? 2 C2H6    +  7 O2   ----->  4  CO2   +  6  H2O 0.90 grams of ethane

  25. Download/Link Std Dev mod 7 limiting reactant 24 Limiting Reactants • Limiting Reactant - The reactant in a chemical reaction that limits the amount of product that can be formed.  The reaction will stop when all of the limiting reactant is consumed. Example: I want to assemble a gadget that requires one nut, one bolt and two washers for every hole. I have in my garage a bucket filled with 12 washers, 4 bolts and five nuts. What is the LIMITING SMALL METAL OBJECT? Goal: Demonstrate the conceptual principle of limiting reactants

  26. How To… 1-Calculate how much can be made by both. The one with the least amount is the LR. Limiting Reactants Calculations Example 1: You combine 10.0 grams of hydrogen gas and 15.0 grams of oxygen gas. How many grams of water vapor are made? Which is the limiting reactant? 2H2 + O22H2O Oxygen is limiting reactant, as the amount of H2O is much less than that produced by hydrogen. 25 http://www.lynden.wednet.edu/cms/lib02/WA01001013/Centricity/Domain/93/Chemistry%20Text/Limiting%20Reactant%20Problems%20text.pdf

  27. How To… 1-Calculate how much can be made by both. The one with the least amount is the LR. Limiting Reactants Example 2: If 5.00 grams of copper metal react with a solution containing 20.0 grams of AgNO3, which reactant is limiting and what mass silver is produced? A copper (II) product is formed. 26

  28. Limiting Reactants-Practice with a friend 27 1) 10.0g of aluminum reacts with 35.0 grams of chlorine gas to produce aluminum chloride. Which reactant is limiting? 2 Al + 3 Cl2 2 AlCl3 CaO + 2HCl → CaCl2 + H2O 2)75 grams of calcium oxide react with 130 grams of hydrochloric acid to produce a salt and water. What is the limiting reactant?

  29. Limiting Reactants -Practice with a friend 28 Cu (s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag (s) 3) 5g of copper metal react with a solution containing 20g of silver nitrate to produce copper (II) nitrate and silver. Al2S3 + 6 H2O → 2 Al(OH)3 + 3 H2S 4) 15.00 g of aluminum sulfide and 10.00 g of water react until the limiting reagent is consumed.

  30. 29 Reversible Reactions • A reversible reaction is one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. • Most reactions are reversible. Some are not- • EX: • burning, • combustion.

  31. 30 Std Dev Dynamic Equilibrium Equilibrium • At equilibrium, the concentration of all reactants and products stays constant.

  32. Dynamic Equilibrium 31 • It seems as if nothing is happening, because the macroscopic properties, those you can see (e.g. color and temperature), do not change. However, at the microscopic level there is continual change. • No “NET” change occurs. • It is a DYNAMIC STATE Note: When the concentration of products stays constant and the concentration of reactants stays constant, the system is at equilibrium.

  33. Dynamic Equilibrium 32 • Amounts are not always 50/50 at equilibrium. • Depends on which one is more favorable (products or reactants) • Equilibrium refers mainly to the RATE of the reaction. Not the amounts of product and reactant.

  34. Factors Affecting Equilibrium: 33 Le Chatelier’s Principle Video Clip • Le Chatelier’s Principle • If stress is applied to a system in equilibrium, the system changes in a way that relieves the stress. • Adding more reactant or product • Change the temperature • Change the Pressure

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  38. Baking Soda Lab Video

  39. Reaction of Stoichiometry Calculations Fe2O3 + 3CO ----> 2Fe + 3CO2 Questions we could ask about the reaction…. Question #1: How many CO molecules are required to react with 25 formula units of Fe2O3? Question #2. How many Fe atoms are produced by reaction of 2.5 x 105 formula units of Fe2O3with excess CO?

  40. Fe2O3 + 3CO ----> 2Fe + 3CO2 Question #3: What mass of CO is required to react with 146 grams of Fe2O3? Question #4: What mass of CO2 can be produced by the reaction of 0.540 moles of Fe2O3? …with excess CO?

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