SToichiometry

Law of Conservation of Mass Antoine Lavoisier Studied combustion Showed it involved oxygen & life is supported by oxygen in a process similar to combustion Carefully weighted reactants & products In an (ordinary) chemical reaction, mass is neither created nor destroyed. Wrote first modern chemistry book Worked as a tax collector during French Revolution Considered enemy of the peopleSent to guillotine

Law of Conservation of Mass All atoms you start with you end up with Need to show conservation of mass with balanced equation Reactant + Reactant --> Product Combustion: Burning in the presence of oxygen Heat is evolved Combustion of hydrocarbonProduces CO2 & Water Combustion:It is usually easiest to balance carbon first hydrogen second count how many oxygen needed in products C5H12 + O2 --> H2O + CO2 5 6 Need 16 oxygen for products 8

Mass-Mass & Mole-Mole Relations in Reactions Suggested method: 1. write balanced equation CO + 2 H 2 --> CH 3 OH 2. Make Chart Grams Molar Mass Moles have Given g of each reactant, a. which is limiting reactant b. how much of reactant in excess is left c. How much product, in grams g 28.0 g/mol2.00 g/mol ______ / / / / 3.57 mol50.0 mol 3. Pick one take moles have & divide by balanced coefficient This gives you a ratio to multiply other coefficients by 3.57/1 = 3.57 Moles use3.57 mol 4. Take answer from step 3 multiply other coefficient by it 3.57 x 2 = mol Moles left mol Grams left085.8 g 3.57 x 1 = mol 32.0 g/mol 114. g CO 85.8 g 114. g Theoretical yield Percent yield = (actual yield/ theoretical yield) 100 Let’s say you got g for this reaction Percent yield = (100.0 g / 114. g) 100 = 87.7 %

You might have your own method for stoichiometry-- that’s fine too.