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Final Information

Final Information. Open-ended: 6/11 (review 6/10) Last day to ask questions for MC 6/14 Topics: Bonding Reactions Chemical Equations (balancing, types) Percent Composition Molar Mass, Avogadro’s Number, conversions Empirical Formula Stoichiometry Limiting reactants

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Final Information

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  1. Final Information • Open-ended: 6/11 (review 6/10) • Last day to ask questions for MC 6/14 • Topics: • Bonding • Reactions • Chemical Equations (balancing, types) • Percent Composition • Molar Mass, Avogadro’s Number, conversions • Empirical Formula • Stoichiometry • Limiting reactants • Mole-mole, grams-grams, particles-particles conversions

  2. Stoichiometry

  3. Flowchart Atoms or Molecules Divide by 6.02 X 1023 Multiply by 6.02 X 1023 Moles Multiply by atomic/molar mass from periodic table Divide by atomic/molar mass from periodic table Mass (grams)

  4. Calculations molar mass Avogadro’s numberGrams Moles particles Everything must go through Moles!!!

  5. Chemistry Recipes • Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe) • Be sure you have a balanced reaction before you start! • Example: 2 Na + Cl2  2 NaCl • This reaction tells us that by mixing 2 moles of sodium with 1 mole of chlorine we will get 2 moles of sodium chloride • What if we wanted 4 moles of NaCl? 10 moles? 50 moles?

  6. Example Questions • Write the balanced reaction for hydrogen gas reacting with oxygen gas. 2 H2 + O2 2 H2O • How many moles of reactants are needed? • What if we wanted 4 moles of water? • What if we had 3 moles of oxygen, how much hydrogen would we need to react, and how much water would we get? • What if we had 50 moles of hydrogen, how much oxygen would we need, and how much water produced?

  7. 6 mol H2O 4 mol NO 11.33 mol NO 0.2112 mol H2O x x = = 6 mol H2O 5 mol O2 Stoichiometry questions (1) Consider : 4NH3 + 5O2 6H2O + 4NO • How many moles of H2O are produced if 0.176 mol of O2 are used? • How many moles of NO are produced in the reaction if 17 mol of H2O are also produced? # mol H2O= 0.176 mol O2 # mol NO= 17 mol H2O Notice that a correctly balanced equation is essential to get the right answer

  8. 6 mol H2O 32 g O2 18.02 g H2O 5 mol O2 8 g O2 51.4 g H2O x x x x = = 6 mol H2O 1 mol H2O 4 mol NH3 1 mol O2 Stoichiometry questions (2) Consider : 4NH3 + 5O2 6H2O + 4NO • How many grams of H2O are produced if 1.9 mol of NH3 are combined with excess oxygen? • How many grams of O2 are required to produce 0.3 mol of H2O? # g H2O= 1.9 mol NH3 # g O2= 0.3 mol H2O

  9. Mass-Mass Conversions • Most often we are given a starting mass and want to find out the mass of a product we will get (called theoretical yield) or how much of another reactant we need to completely react with it (no leftover ingredients!) • Now we must go from grams to moles, mole ratio, and back to grams of compound we are interested in

  10. Mass-Mass Conversion • Ex. Calculate how many grams of ammonia are produced when you react 2.00g of nitrogen with excess hydrogen. • N2 + 3 H2  2 NH3 2.00g N2 1 mol N2 2 mol NH3 17.06g NH3 28.02g N2 1 mol N2 1 mol NH3 = 2.4 g NH3

  11. 4 mol NO 30.01 g NO 1 mol O2 x x x 5 mol O2 1 mol NO 32 g O2 = 9.0 g NO Stoichiometry questions (3) Consider : 4NH3 + 5O2 6H2O + 4NO • How many grams of NO is produced if 12 g of O2 is combined with excess ammonia? # g NO= 12 g O2

  12. Converting grams to grams • Notice that we cannot directly convert from grams of one compound to grams of another. Instead we have to go through moles. • Many stoichiometry problems follow a pattern: grams(x)  moles(x)  moles(y)  grams(y) • We can start anywhere along this path depending on the question we want to answer Q- for the reaction 2H2 + O2  2H2O what is the path we would take for the following • Given 2 moles H2O, calculate grams H2O? • Moles O2 required for 36 g H2? • Grams of H2O produced from 6 grams O2? • Notice that we cannot directly convert from grams of one compound to grams of another. Instead we have to go through moles. • Many stoichiometry problems follow a pattern: grams(x)  moles(x)  moles(y)  grams(y) • We can start anywhere along this path depending on the question we want to answer Q- for the reaction 2H2 + O2  2H2O what is the path we would take for the following • Given 2 moles H2O, calculate grams H2O? • Moles O2 required for 36 g H2? • Grams of H2O produced from 6 grams O2? • Notice that we cannot directly convert from grams of one compound to grams of another. Instead we have to go through moles. • Many stoichiometry problems follow a pattern: grams(x)  moles(x)  moles(y)  grams(y) • We can start anywhere along this path depending on the question we want to answer Q- for the reaction 2H2 + O2  2H2O what is the path we would take for the following • Given 2 moles H2O, calculate grams H2O? • Moles O2 required for 36 g H2? • Grams of H2O produced from 6 grams O2? • Notice that we cannot directly convert from grams of one compound to grams of another. Instead we have to go through moles. • Many stoichiometry problems follow a pattern: grams(x)  moles(x)  moles(y)  grams(y) • We can start anywhere along this path depending on the question we want to answer Q- for the reaction 2H2 + O2  2H2O what is the path we would take for the following • Given 2 moles H2O, calculate grams H2O? • Moles O2 required for 36 g H2? • Grams of H2O produced from 6 grams O2?

  13. Molar mass of x Molar mass of y Mole ratio from balanced equation Moving along the stoichiometry path • We always use the same type of information to make the jumps between steps: grams (x)  moles (x)  moles (y)  grams (y) Given: 4NH3 + 5O2 6H2O + 4NO a) How many moles of H2O can be made using 0.5 mol NH3? b) what mass of NH3 is needed to make 1.5 mol NO? c) how many grams of NO can be made from 120 g of NH3?

  14. 1 mol NH3 6 mol H2O 30.01 g NO 4 mol NO 4 mol NH3 17.04 g NH3 0.75 mol H2O 25.6 g NH3 x x x x x x = = 17.04gNH3 1 mol NH3 4 mol NO 4 mol NH3 4 mol NH3 1 mol NO = 211 g NO Answers # mol H2O= 0.5 mol NH3 4NH3 + 5O2 6H2O + 4NO a) b) c) # g NH3= 1.5 mol NO # g NO= 120 g NH3

  15. More Stoichiometry Questions Follow the rules for significant digits. Show all calculations. 1. 2 C4H10 + 13 O2 -> 8 CO2 + 10 H2O a) what mass of O2 will react with 400 g C4H10? b) how many moles of water are formed in a)? 2. 3 HCl + Al(OH)3 -> 3 H2O + AlCl3 How many grams of aluminum hydroxide will react with 5.3 moles of HCl? 3. Ca(ClO3)2 -> CaCl2 + 3 O2 What mass of O2 results from the decomposition of 1.00 kg of calcium chlorate? 4. The reaction of Ca with water can be predicted using the activity series. What mass of water is needed to completely react with 2.35 g of Ca?

  16. 5. Fe2O3 + 3CO -> 2Fe + 3CO2. • How many moles of carbon monoxide are required to react with 163.0 g of iron(III) oxide? • How many grams of CO2 are produced from a reaction that also produces 23.9 grams of Fe? 6. 3Cu + 8HNO3 3Cu(NO3)2 + 4H2O + 2NO • how many moles of copper(II) nitrate can be prepared from 17.0 moles of Cu? • how many grams of copper(II) nitrate can be prepared using 3.8 moles of HNO3? • what mass of water results from the reaction of 8.50 kg of copper metal? For more lessons, visit www.chalkbored.com

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