Video 9-1 Reaction Stoichiometry Steps for Problem Solving

CHAPTER 9 STOICHIOMETRY

I. Reaction Stoichiometry  Review: Change the following into moles:  34.8 grams of hydrogen (MM = )  7.35 x molecules of water

I. Reaction Stoichiometry  Using BALANCED CHEMICAL EQUATIONS, you can determine mass (or particle or mole) relationships between reactants and products in a chemical reaction.

I. Reaction Stoichiometry a XY + b QZ  c AB + d CD Moles XY Grams XY Particles XY Moles QZ Moles AB Moles CD

I. Reaction Stoichiometry a XY + b QZ  c AB + d CD  Mole ratios come from the COEFFICIENTS in the balanced equations.

II. Steps for Problem Solving 1.Determine the products of the reaction and write the complete equation. 2.Balance the equation. 3.Determine what you are LOOKING FOR (“WANTED”) 4.Determine what you are starting with (“GIVEN”).

II. Steps for Problem Solving 5.Use dimensional analysis to change the “given” into the “wanted”.  Ex. How much oxygen is required to burn grams of methane (CH 4 )? How many grams of each product are formed? NOTE: This problem assumes you have an unlimited (excess) amount of oxygen.

Video 9-2 Limiting Reactants Percent Yield

III. Limiting Reactants (Reagents)  Limiting Reactant—limits the amount of product formed. Also determines how much of the other reactant (excess reactant) can be used in the reaction.  Stoichiometric quantities: all reactants are exactly used up (no excess reactants)

III. Limiting Reactants (Reagents)  2 ways to determine which is the limiting reactant:  A. Determine how much of the second reactant is needed to use up the first one. 1.Select one of the reactants. Change it into moles. 2.Change those moles into moles of the second reactant.

III. Limiting Reactants (Reagents) 3.Change moles into the unit given for that second reactant (grams, molecules, etc.). 4.Compare this quantity with the given quantity for this reactant. If you have this much, the first reactant can all be used up  1st reactant is limiting reactant.

III. Limiting Reactants (Reagents)  B. Determine how much product each reactant can produce. 1.Change the given quantity of each reactant into MOLES of one of the products (choose the same product for both conversions). 2.Whichever reactant produces the LEAST amount of product is the limiting reactant.

III. Limiting Reactants (Reagents)  Ex. If 15.0 grams of oxygen and 5.00 grams of hydrogen react, how many grams of product will be produced? How much excess reactant will be left over?

IV. Percent Yield  Theoretical yield: CALCULATED amount of product that should be produced from a given chemical reaction  Actual yield: measured amount of product obtained from the reaction when it is actually done.

IV. Percent Yield  Sometimes (due to errors in actually conducting the reaction), theoretical yield  actual yield  Percent yield = (actual yield / theoretical yield) x 100% Given in problem or determined by actually doing the reaction CALCULATED using stoichiometry and methods learned earlier

IV. Percent Yield  Ex. A student reacts 15.0 grams of oxygen with 5.00 grams of hydrogen. The student obtains 15.5 grams of product. What is the percent yield of the reaction?

IV. Percent Yield  Ex. How much product is collected from the reaction between grams of nitrogen and excess hydrogen if the percent yield is 87.34%?