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Formulas, Equations, and Stoichiometry

Formulas, Equations, and Stoichiometry. Chemical Equations. Both sides of the chemical equation must be balanced. Can only change the coefficient, not the subscripts, to balance the equation. Example: methane gas burning to produce carbon dioxide and water.

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Formulas, Equations, and Stoichiometry

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  1. Formulas, Equations, and Stoichiometry

  2. Chemical Equations • Both sides of the chemical equation must be balanced. • Can only change the coefficient, not the subscripts, to balance the equation. Example: methane gas burning to produce carbon dioxide and water. Unbalanced: CH4 + O2 CO2 + H2O Balanced: CH4 + 2O2 CO2 + 2H2O

  3. Balance the following: • Na + H2O  NaOH + H2 • Fe + O2  Fe2O3 • C2H4 + O2  CO2 + H2O 2 2 2 4 3 2 3 2 2

  4. Formula or Molecular Mass • Sum of the atomic weights of each atom in a substance’s chemical formula Formula weight of sucrose, C12H22O11: 12 C atoms = 12 (12.0 amu) = 144.0 amu 22 H atoms = 22 (1.0 amu) = 22.0 amu 11 O atoms = 11 (16.0 amu) = 176.0 amu Formula weight = 342.0 amu

  5. Percent Composition 144.0 amu C / 342.0 amu C12H22O11 = .421 (.421) x 100 = 42.1% 22.0 amu H / 342.0 amu C12H22O11 = .064 (.064) x 100 = 6.4% 176.0 amu O / 342.0 amu C12H22O11 = .515 (.515) x 100 = 51.5%

  6. Example • Calculate percentage of nitrogen, by mass, in Ca(NO3)2

  7. Moles • 1 mol of X= 6.02 x 1023 of X = molar mass of X • 1 g = 6.02 x 1023 amu 1 mole C atoms = 6.02 x 1023 C atoms = 12g C 1 carbon atom = 12amu

  8. Calculate • Number of H atoms in .350 mol of C12H22O11 • Number of O atoms in .25 mol of Ca(NO3)2 • Formula weight or molecular weight of Ca(NO3)2 • Molar mass of Ca(NO3)2 • Moles of Sucrose, C12H22O11, in 5.3 g of sucrose • Molecules of sucrose in 5.3 g of sucrose

  9. Formulas • Empirical formula: chemical formula giving only the relative number of atoms of each type in a molecule. • Molecular formula: chemical formula giving the actual number of atoms of each type in a molecule. • Example: • Empirical formula: HO CH2 • Molecular formula: H2O2 C2H4

  10. Calculate • Ascorbic Acid (vitamin C) contains 40.92% C, 4.58% H and 54.50% O by mass. What is the empirical formula? • If the molar mass of Ascorbic Acid is 176g, what is the molecular formula? C3H4O3 C6H8O6

  11. Stoichiometry and Limiting Reactants

  12. Percent Yield

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