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Stoichiometry

AP Chemistry. Stoichiometry. In the thermite reaction, a mixture of powdered aluminum and powdered iron(III) oxide react to yield iron and aluminum oxide. The reaction burns hot enough to be useful in under- water welding. 2 Al + Fe 2 O 3  2 Fe + Al 2 O 3 + energy.

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Stoichiometry

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  1. AP Chemistry Stoichiometry In the thermite reaction, a mixture of powdered aluminum and powdered iron(III) oxide react to yield iron and aluminum oxide. The reaction burns hot enough to be useful in under- water welding. 2 Al + Fe2O3 2 Fe + Al2O3 + energy

  2. Chemical Equations In a reaction: atoms are rearranged mass AND are conserved energy charge Balancing Chemical Equations law of conservation of mass same # of atoms of each type on each side of equation = Hint: Start with most complicated substances first and leave simplest substances for last.

  3. Solid lithumreacts w/oxygen to form solid lithium oxide. Li+ O2– 4 2 Li(s) + O2(g) Li2O(s) + Aqueous aluminum sulfate reacts w/aqueous barium chloride to form a white precipitate of barium sulfate. The other compound remains in solution. Ba2+ Al3+ SO42– Cl– 3 3 2 + + AlCl3 BaSO4 Al2(SO4)3 BaCl2 (aq) (s) (aq) (aq)

  4. CaC2(s) + H2O(l) C2H2(g) + CaO(s) CaSi2+ SbI3 Si + Sb+ CaI2 Al + CH3OH Al(CH3O)3+ H2 Methane gas (CH4) reacts with oxygen to form carbon dioxide gas and water vapor. Furnaces burn primarily methane. 2 2 CH4(g) O2(g) H2O(g) CO2(g) + + 3 2 6 2 3 3 2 6 2 3

  5. alkali metal metal hydroxide hydrogen gas + water + 2 2 5 4 2 C2H2(g) + O2(g) CO2(g) + H2O(l) 5 3 4 C3H8 + O2CO2 + H2O 8 4 10 2 5 C4H10+ O2 CO2+ H2O 13 Complete combustion of a hydrocarbon, or of a compound containing C, H, and O (e.g., methanol, CH3OH) yields CO2 and H2O. Another pattern of reactivity: e.g., 2 Rb(s) + 2 H2O(l)  2 RbOH(aq) + H2(g)

  6. Two (of the several) Types of Reactions combination (synthesis): simpler substances combine to form more complex substances -- form: A + B  AB AB + C  ABC A + B + C  ABC sodium + chlorine gas sodium chloride + Na 2 2 NaCl Cl2

  7. lithium chlorate lithium chloride + oxygen water hydrogen gas + oxygen gas decomposition: complex substances are broken down into simpler ones -- form: AB  A + B ABC  AB + C ABC  A + B + C Li+ Li+ ClO3– Cl– 2 3 2 + O2 LiClO3 LiCl 2 2 + O2 H2O H2

  8. formula weight: the mass of all of the atoms in a chemical formula (unit is amu) -- If the substance is a molecular substance (e.g., C3H8), then the term molecular weight is also used. molar mass: the mass of one mole of a substance (unit is usually grams) -- recall that 1 mole of any substance 6.02 x 1023 particles of that substance =

  9. Find the molar mass and formula weight of ammonium phosphate. NH4+ PO43– N: = 42.0 g 3 (14.0 g) (NH4)3PO4 (1.0 g) H: 12 = 12.0 g m.m. = 149.0 g P: = 31.0 g 1 (31.0 g) O: = 64.0 g 4 (16.0 g) f.w. = 149.0 amu

  10. g element x 100 % of element = molar mass of compound percentage composition: the mass % of each element in a compound equation: Find the percentage of oxygen, by mass, in calcium nitrate. Ca(NO3)2 % O = = 58.5% O

  11. shows the true number and type of atoms in a m’cule lowest-terms formula Empirical Formula and Molecular Formula CH2O C3H8 C2H5 C5H4 C12H22O11 C4H9

  12. Finding an Empirical Formula from Experimental Data 1. Find # of g of each element. 2. Convert each g to mol. 3. Divide each “# of mol” by the smallest “# of mol.” 4. Use ratio to find formula. “What’s your flavor of ice cream?”

  13. A ruthenium/sulfur compound is 67.7% Ru. Find its empirical formula. RuS1.5 Ru2S3

  14. A sample of a compound contains 4.63 g lead, 1.25 g nitrogen, and 2.87 g oxygen. Name the compound. ? PbN4O8 ? Pb(NO2)4 lead(IV) nitrite Pb? 4 NO2–

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