CHAPTER 3: STOICHIOMETRY: CALCULATIONS WITH CHEMICAL FORMULAS AND EQUATIONS STOICHIOMETRY-quantitative relationships between amounts of reactants and products Quantitative (How Much) -Balanced Chem. Eq. -Calc of Average AW -Calc of MW and FW - Calc of # moles

- Use of N to determine # of atoms, molecules, or ions in a sample -Use of N to determine mass of atom, ion, or molecule - % comp. from formula -empirical formula from comp -Determine amounts of product from a given amount of reactant - % Yield -Limiting Reactant

Balance Chem Rx by inspection (trial and error) Types of Rx -Combustion -Decomposition -Combination In balancing a reaction (same number and type of atoms on both sides of the equation) you may NEVER change the formula (subscripts) of a reactant or product only its balancing coeff.

Balance the combustion reaction of CH4 in air

Examples of combination and decomposition reactions

amu scale (AW, FW, MW) MOLECULAR WEIGHT and FORMULA WEIGHT refer to

molecular and ionic cpds and are calculated as the sum of Atomic Weights. (has the same meaning as molar mass) Determine FW or MW of H2O, NaOH, and Ca(NO3)2 Calculate the % O in the same samples. Mole (mol) is the SI unit for the amount of a substance. A mole (of anything) contains as many

elementary particles as there are in exactly 12g of 12C ( 6.02x1023 particles) Avogadro's Number, N- the number of particles in one mole of any substance N=6.02214199x1023 part./mol How long would it take to spend N dollars if you could spend at a million $/second Calc of # moles (VERY

IMP)

Molar Mass (g/mol) - the mass in g of one mole of any substance. The Molar Mass is numerically equal to the Atomic Weight (AW), Formula Weight (FW), or Molecular Weight (MW )

g/mol)molarmass(mass(g)=mol

expressed in amu. Determine the number of moles in 10.0g of: NaOH, H2O, and Ca(NO3)2 Determine the number of oxygen atoms in 10.0g of the same substances. Calculate the mass in g of a single water molecule -Use %composition to obtain empirical formula

element #moles K .104 C .052 O .156 Determine the EMP formula of the following cpd. element %comp. C 58.77 H 13.81 N 27.40 What is the molecular

formula if the molecular weight was determined to be 306g/mol Determine the EMP formula of the following cpd. element %comp. C 61.59 H 11.7 N 26.92

What is the molecular formula if the molecular weight was determined to be 468 g/mol Determine the molecular formula of ibuprofen if its molar mass is 206 g/mol and it contains 75.69%C, 8.80% H, and 15.51% O. Calculate the mass of carbon dioxide and water that are produced and the amount of oxygen consumed in the complete

combustion of 100. g of methane. Determine the amount of nitrogen consumed and ammonia produced if 5.00 g of hydrogen is consumed. N2(g) + 3H2(g) → 2 NH3 (g) Mass to Mass Conv. Proc. 1. Take given info. in g and convert to moles (Divide by Molar Mass) 2. Convert from moles of

given species to moles of desired species (Use coefficients from balanced chem Eq) 3. Convert from moles to grams (Multiply by Molar Mass)

Determine the % Yield of ammonia if 9.50g of ammonia is obtained. %Yield=Actual/Theo.*100

Determine the amount of product in the reaction of 4 moles of O2 and 9 moles of H2. How much of the excess reactant is left over? Limiting Reactant problems can be identified if amounts of two (or more) reactants are specified. How much product is

produced from the reaction of 10.00 g of Na and 4.00 g of O2 ? How much of the excess reactant is left over? How many dozen brownies can you prepare from 10 eggs, 3 cups of butter, and 7 cups of milk if your recipe calls for 4 eggs, 1 cup of butter, and 2 cups of milk for a dozen

brownies. Limiting Reactant- the reactant that is completely consumed in a chemical rx and determines the amount of product that can be obtained. (The other reactant(s) is in excess) Limiting Reactant Problems -determine moles of each reactant -divide # moles by

balancing coeff. -smaller # is L.R. -amt. product is based on LR