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Section 3.3 Stoichiometry and Chemical Reactions

Section 3.3 Stoichiometry and Chemical Reactions. In this section: a. Chemical reactions and equations b. Balancing equations c. Reaction stoichiometry. Chemical reactions and equations Reactants Products. CH 3 CHCH 2 + HCl. CH 3 CHClCH 3.

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Section 3.3 Stoichiometry and Chemical Reactions

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  1. Section 3.3Stoichiometry and Chemical Reactions

  2. In this section:a. Chemical reactions and equationsb. Balancing equationsc. Reaction stoichiometry

  3. Chemical reactions and equations Reactants Products CH3CHCH2 + HCl CH3CHClCH3

  4. Chemical equation: before and afterMechanism: how you get there Step 1. Step 2.

  5. The most important thing: It’s the same atoms Reactants Products CH3CHCH2 + HCl CH3CHClCH3

  6. CH3CHCH2 + HCl CH3CHClCH3 The Law of Conservation of Matter It’s the same atomsStoichiometric Coefficients: C2H2 + 2 H2 CH3CH3

  7. Balancing Chemical EquationsGoal: same number of atoms of each element on both sidesRule: you can change stoichiometry coefficients,not the molecular formulas CH4 + O2 CO2 + H2O

  8. Another Example: Mg + O2MgO A bit harder C4H10 + O2 CO2 + H2O

  9. CH4 + 2 O2 CO2 + 2 H2O Big misconception: stoichiometric coefficients are NOT how much reacts/forms

  10. CH4 + 2 O2 CO2 + 2 H2O Balancing Equation = mol to mol conversion factor

  11. CH4 + 2 O2 CO2 + 2 H2O Amounts tables: If 0.46 mol O2 react, how much CO2 and H2O are formed, and how much CH4 reacts? change:

  12. Real experiments use mass, not moles. gram gram conversionsPath: grams A moles A moles B grams B

  13. 25.0 g of O2 react. What mass of CH4 reacts and what masses of CO2 and H2O are formed? CH4 + 2 O2 CO2 + 2 H2O

  14. 25.0 g of O2 react. What mass of CH4 reacts and what masses of CO2 and H2O are formed? CH4 + 2 O2 CO2 + 2 H2O

  15. Sections 3.4 and 3.5Limiting Reactants, Percent Yield and Chemical Analysis

  16. In these sections:a. Identifying limiting reactantsb. Calculating theoretical yieldc. Calculating percent yieldd. Chemical analysis

  17. The Idea of Limiting Reactants If you have 200 tires and 75 steering wheels, how many cars can you make?

  18. Identifying Limiting Reactants If you have 200 tires and 75 steering wheels, how many cars can you make? 4 tires + 1 steering wheel  1 car Mole Ration Method: Maximum Product Method:

  19. Using Amounts Tables: after determining limiting reactant Initial amounts: Fe2O3: 100 g = 0.626 mol C: 50.0 g = 4.16 mol 2 Fe2O3 + 3 C  4 Fe + 3 CO2 initial change final

  20. Percent Yield

  21. Alum Lab Calculations: Let’s say you start with 0.985 g Al and actually make 14.8 g KAl(SO4)212 H2O product. What is the percent yield? Molar masses: Al = 26.98 g/mol; KAl(SO4)212 H2O = 474.37 g/mol

  22. Chemical Analysis: Using stoichiometry to determining how much of one thing is in another A sample of soil is analyzed for the element iodine. A 2.68-g sample is treated so all the iodine containing compounds dissolve and the iodine is converted to iodide ion. The solution is treated with dissolved Pb2+ ion, and the following reaction occurs: Pb2+(aq) + 2 I-(aq)  PbI2(s) If 0.339 g of PbI2 are obtained, what was the percent iodine in the original sample?

  23. Chemical Analysis: Determining FormulasCHO Analyzer burn: 0.588 g sample collect: 0.240 g H2O 0.882 g CO2

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