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Stoichiometry

Stoichiometry. Stoichiometry comes from the Greek words: Stoichion- meaning element Metron- meaning to measure. There are four types of problems: Mole-Mole Mole-Mass Mass-Mole Mass-Mass. Stoichiometry is a branch of chemistry dealing with mass and mole relationships. Write down: Given

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Stoichiometry

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  1. Stoichiometry

  2. Stoichiometry comes from the Greek words: Stoichion- meaning element Metron- meaning to measure There are four types of problems: Mole-Mole Mole-Mass Mass-Mole Mass-Mass Stoichiometry is a branch of chemistry dealing with mass and mole relationships

  3. Write down: Given Unknown Mole ratio- should compare the given and unknown Molar Mass-only needed if unknown is asked for in grams or if given is in grams Mole Ratio- is a conversion factor relating number of moles of any two substances involved in a chemical reaction Remember… a mole is the SI unit for amount To solve stoichiometry problems, use the following problem solving steps:

  4. Practice Writing Mole Ratios • 2Al2O3 -- >4Al +3O2 2 mol Al2O3 4 mol Al 3 molO2 4 mol Al 2 mol Al2O3 4 mol Al

  5. 3H2 + N2 2NH3 • Write the mole ratio that compares hydrogen to nitrogen. • Write the mole ratio that compares nitrogen to ammonia. • Write the mole ratio that compares ammonia to nitrogen.

  6. Practice Problems: • How many moles of ammonia are produced when 6 moles of hydrogen gas react with an excess of nitrogen gas? 3H2 + N2 2NH3 ***Make sure the equation is balanced.

  7. When Mg burn in air, it combines with oxygen to form MgO. What mass in grams of MgO is produced from 2.00 moles of Mg? 2Mg + O2 2MgO

  8. How many moles of mercury (II) oxide are needed to produce 125 grams of oxygen? • Laughing gas (N2O) is produced from the decomposition of ammonium nitrate. Water is also a product. How many grams of ammonium nitrate are required to produce 33.0 g of laughing gas? If 20.0 grams of laughing gas is produced, how many grams of water is also formed?

  9. Stoichiometry WS#1 • 2Al + 3Cl2 2AlCl3 • 2KClO3  2KCl + 3O2 • 2Ag2O  4Ag + O2

  10. Stoichiometry WS#2 • Li3N + 3H2O  3LiOH + NH3 • Cl2 + 2NaI  2NaCl + I2 • 2C4H10 + 13O2  8CO2 + 10H2O • Ni(NO3)2 + 2NaOH  Ni(OH)2 + 2NaNO3 5. Ba(OH)2 + H2SO4  BaSO4 + 2H2O 6. Na2O + H2O  2NaOH • 3Zn + 2AlBr3  3ZnBr2 + 2Al • Al2(CO3)3 Al2O3 + 3CO2 9. 2KClO3 2KCl + 3O2 • 2HCl + Zn  ZnCl2 + H2 • Zn + Cl2 ZnCl2

  11. Controls the amount of product formed in a chemical reaction because it is the reactant that you do not have enough of. The excess reactant is the reactant that is not used up and is found in excess once the reaction is complete. Limiting Reactants

  12. To Determine the Limiting Reactant: • Amounts of both reactants will be given: choose one reactant to be your given and the other to be your unknown. • Start with reactant that is the given and find how much of the unknown would be required. • Compare your answer (which tells you how much you needed) with the amount of the unknown in the problem (which tells you how much you actually have). If what you have is less than what is needed, the reactant is limiting. If what you have is more than needed, it is the excess reactant.

  13. Example: • If 34.0 g of HCl is added to 12.0 g of Al(OH)3, is there enough Al(OH)3 to completely react with the acid? 3HCl + Al(OH)3  AlCl3 + 3H2O

  14. More Examples: TiCl4 + O2 TiO2 + Cl2 a)If 4.5 mole of TiCl4 is reacted with 3.5 mol O2, determine the limiting reactant. b) How many moles of the excess reactant will remain if the reaction goes to completion? (Hint: Start with the limiting reactant as your given and determine how much of the excess would be used-subtract the amount of excess used from the amount that you had in the problem)

  15. c) How many moles of each product should be formed if the reaction goes to completion? (Hint: Since the limiting reactant controls the amount of product produced, you must use the amount of the limiting given in the problem to calculate product.)

  16. Used to rate the efficiency of a reaction = actual yield x 100 theoretical yield REMEMBER.. Yield means product!!! The actual yield will always be what you produce. The theoretical yield is what should have been produced with the amount of the reactant given. Percent Yield

  17. Examples: P4O10 + 6H2O  4H3PO4 When 100.0 g of P4O10 is reacted, 126.24 g of phosphoric acid is produced. Determine the % yield. • Start with the amount of reactant given (blue) and determine how much of the product should be produced. This will be your theoretical yield. • Divide the actual yield (yellow) by theoretical and multiply by 100.

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