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Mastering Stoichiometry: Understanding Chemical Quantity Relationships

Explore stoichiometry, ratios in chemical reactions, and using ratios to determine unknown quantities. Learn to convert between mass, volume, moles, and number of atoms in reactions. Solve stoichiometric problems efficiently.

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Mastering Stoichiometry: Understanding Chemical Quantity Relationships

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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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