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Stoichiometry

Stoichiometry. I. Quantity in Chemical Reactions. stoicheion (stoicheion) = element metreion (metreion) = measurement Stoichiometry = measurement of the quantities in chemical reactions. I. Quantity in Chemical Reactions. A. What goes in = what comes out

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Stoichiometry

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  1. Stoichiometry

  2. I.Quantity in Chemical Reactions • stoicheion (stoicheion) = element • metreion (metreion) = measurement • Stoichiometry = measurement of the quantities in chemical reactions

  3. I.Quantity in Chemical Reactions A.What goes in = what comes out • Atoms aren’t created or destroyed, they just combine in different ways

  4. I.Quantity in Chemical Reactions B.Ratios in chemical equations • Coefficients of chemicals in balanced reactions show ratios between elements • Example: 2H2O  2H2 + O2 • Ratio: 2 molecules H2O : 2 molecules H2 : 1 molecule O2

  5. I.Quantity in Chemical Reactions C.Using ratios • Ratios can be used to determine unknown quantities from known quantities.

  6. 4 atoms Al x atoms Al 3 molecules O2 6 molecules O2 (4 atoms Al) (4 atoms Al) (6 molecules O2) (6 molecules O2) = (3 molecules O2) = (3 molecules O2) (x atoms Al) C.Using ratios Example: 4Al + 3O2 2Al2O3 How many Al atoms are needed to fully react with 6 O2 molecules? 4 atoms Al : 3 molecules O2 : 2 compounds Al2O3 = x atoms Al 8 atoms Al

  7. 4 atoms Al x atoms Al 2 comp. Al2O3 16 comp. Al2O3 (4 atoms Al) (4 atoms Al) (16 comp. Al2O3) (16 comp. Al2O3) = (2 comp. Al2O3) = (2 comp. Al2O3) (x atoms Al) C.Using ratios Example: 4Al + 3O2 2Al2O3 If you want 16 Al2O3 compounds, how many Al atoms and how many O2 molecules will you need? 4 atoms Al : 3 molecules O2 : 2 compounds Al2O3 = x atoms Al 32 atoms Al

  8. I.Quantity in Chemical Reactions D.Atoms aren’t a useful unit in the laboratory • Instead of using atoms in the laboratory, we use larger quantities. • Ratios only show relationships between numbers of chemicals – NOT mass or volume • We can convert between mass, volume, number, and moles • The ratio is the MOLAR RATIO

  9. 1 atom Mg x atoms Mg 1 comp. MgCl2 6.02x1023 comp. MgCl2 (1 atom Mg) (6.02x1023 comp. MgCl2) (1 atom Mg) (6.02x1023 comp. MgCl2) = (1 comp. MgCl2) = (1 comp. MgCl2) (x atoms Mg) Using ratios, take 2 Example: Mg + 2HCl  MgCl2 + H2 How many atoms of Mg are necessary to produce 6.02x1023 compounds of MgCl2? 1 atom Mg : 2 comp. HCl : 1 comp. MgCl2 : 1 molecule H2 = 6.02x1023 atoms Mg x atoms Mg

  10. (1 mole Mg) ( 1 mole MgCl2) = (1 mole MgCl2) 1 mole Mg x moles Mg 1 mole MgCl2 1 mole MgCl2 (1 mole Mg) (1 mole MgCl2) = (1 mole MgCl2) (x moles Mg) Using ratios, take 2 Example: Mg + 2HCl  MgCl2 + H2 How many moles of Mg are necessary to produce 1 mole of MgCl2? 1 mole Mg : 2 moles HCl : 1 mole MgCl2 : 1 mole H2 = 1 mole Mg x moles Mg

  11. 1 mole O2 x moles O2 2 moles H2O2 17.3 moles H2O2 (1 mole O2) (17.3 moles H2O2) = (2 moles H2O2) (x moles O2) (1 mole O2) (17.3 moles H2O2) = (2 moles H2O2) E.Solving Stoichiometric Problems In the reaction 2H2O2 2H2O + O2 how many moles of oxygen molecules are produced if I start with 17.3 moles of hydrogen peroxide (H2O2)? 2 moles H2O2 : 2 moles H2O : 1 mole O2 = 8.65 moles O2 x moles O2

  12. E.Solving Stoichiometric Problems Ammonium nitrate breaks down to form dinitrogen monoxide and water. • Write the equation and balance it: NH4NO3  N2O + 2 H2O 2 N 2 N 4 H 4 X 2 H 3 O 3 X 2 O

  13. 2 moles H2O 55.56 moles H2O 1 mole NH4NO3 x moles NH4NO3 (1 mole NH4NO3) (55.56 moles H2O) = (2 moles H2O) (55.56 moles H2O) (1 mole NH4NO3) = (2 moles H2O) (x moles NH4NO3) E.Solving Stoichiometric Problems • How much ammonium nitrate is needed to form 55.56 moles of water? NH4NO3 N2O + 2H2O 1 mole NH4NO3 : 1 mole N2O : 2 moles H2O = 27.78 moles NH4NO3 x moles NH4NO3

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