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Ch. 9: Stoichiometry

Ch. 9: Stoichiometry. Stoichiometry – pronounced stoy-key-ah-meh-tree . A balanced chemical equation can be interpreted on a molecular level, a mole level, or a mass level. Ex) N2 + 3 H2  2 NH3 The relationship between N 2 and H 2 is: 1 molecule of N 2 = 3 molecules H 2 Or:.

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Ch. 9: Stoichiometry

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  1. Ch. 9: Stoichiometry • Stoichiometry – pronounced stoy-key-ah-meh-tree. • A balanced chemical equation can be interpreted on a molecular level, a mole level, or a mass level. • Ex) N2 + 3 H2  2 NH3 • The relationship between N2 and H2 is: • 1 molecule of N2 = 3 molecules H2 • Or:

  2. Stoichiometry • We can also establish similar relationships between the product and the reactants. • This allows us to convert any amount of N2, H2, and NH3 into a quantity of the others. • Analogy: Making a bicycle. • 1 frame + 2 wheels  1 bicycle • What if you had 40 frames? • What if you made 75 bicycles?

  3. Stoichiometry Fill in the table below.

  4. Stoichiometry It is impractical to do most reactions in terms of molecules. The coefficients can be viewed as “moles.” Thus, 1 mole of N2 plus 3 moles of H2 will produce 2 moles of NH3.

  5. Stoichiometry Fill in the table below.

  6. Stoichiometry Finally, we can calculate any mass from a mole amount using the molar mass of each compound.

  7. Stoichiometry Converting a mass-to-mass of any reactant or product involves three steps. Mass of A Mass of B Divide by Molar Mass of A Multiply by Molar Mass of B Moles of A Moles of B Multiply by the ratio of B / A

  8. Stoichiometry What mass, in grams, can be produced by the complete reaction of 3.40grams of N2?

  9. Stoichiometry What mass of PH3 is possible from the complete reaction of 150.grams of Ca3P2? The balanced reaction is: Ca3P2 + 6 H2O  3 Ca(OH)2 + 2 PH3 What three pieces of information will we need?

  10. Stoichiometry What mass of Br2 is required to react with 0.185grams of Al? The balanced reaction is: 2 Al + 3 Br2  2 AlBr3

  11. Stoichiometry Limiting reactant – amounts used in a reaction may have one (or more) reactant in excess and one in a lesser amount – this is the limiting reactant. Ex) Back to our bicycle assembly – what if the warehouse included 200 frames and 350 wheels. How many bicycles could you make? What is the limiting “reactant”?

  12. Stoichiometry Mole-amounts require the application of the mole-to-mole amounts. Using the reaction: 6 Na + N2  2 Na3N

  13. Stoichiometry Mass amounts require application of the three-step process. In the reaction below, 4.55g of Fe2O3 and 2.85g of CO are allowed to react. What mass of Fe metal is possible? Fe2O3 + 3 CO  2 Fe + 3 CO2

  14. Stoichiometry The amount of product possible based on the limiting reactant is sometimes called the theoretical yield. The percent yield is then the actual yield divided by the theoretical yield times 100.

  15. Stoichiometry When 100.g of CS2 reacts with 100.g of Cl2, 65.0g of CCl4 are produced. Calculate the percent yield of this reaction.

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