Things you must KNOW and what to expect  Things you must KNOW  You must KNOW your polyatomics  You must KNOW how to write a balanced formula  You have to be able to balance a chemical equation  You need to know how to convert from grams to moles and moles to grams.  You need to be able to calculate molar mass  What to expect in this chapter  You will be converting grams to moles of one compound, then using the mole ratio (balanced equation) go to moles of another compound and then from moles to grams in the new compound.  You will learn how to identify a limiting reactant, and how to calculate percent yield.

What is Stoichiometry?  Stoichiometry: the study of quantitative relationships between amounts of reactants used and products formed by a chemical reaction.

Based on the Law of Conservation of Mass (mass reactants = mass products)  To prove Law of Conservation of Mass 1.Start with a balanced equation 2.Coefficient indicates the #molecules/formula units and # of moles 3.Change moles to mass 4.Add up mass reactants and mass of products They should equal C 3 H 8 (g) + 5 O 2 (g)  3 CO 2 (g) + 4 H 2 O(g)

What is Stoichiometry? : continued  Can use balanced chemical equation to get mole ratios 2 Al + 3 Br 2  2 AlBr 3 2 mol Al2 mol Al3 mol Br 2 3 mol Br 2 2 mol AlBr 3 2 mol AlBr 3  Find all the possible mole ratios for: KClO 3 (s)  KCl(s) + O 2 (g)

Stoichiometric Calculations  Use relationships to determine the amount of product formed or reactant needed.  Moles to moles  Moles known x mol unknown mol known from problem ratio from balanced equation =mol unknown

Moles  Moles  How many moles of carbon dioxide are produced when 10.0 moles propane (C 3 H 8 ) are burned in excess oxygen?

1.Write & balance the equation C 3 H O 2  3 CO H 2 O 2.Find the mole ratio between propane and carbon dioxide: 1 mol C 3 H 8 : 3 mol CO 2 3.Multiply ratio by known amount from problem 10 mol C 3 H 8 x 3 mol CO 2 = 30 mol O 2 1 mol C 3 H 8

Moles  Mass  Moles to mass Determine the mass of sodium needed when sodium reacts with 1.25 moles of chlorine gas to form sodium chloride

1.Write & balance the equation 2 Na + Cl 2  2 NaCl 2.Find the mole ratio between propane and carbon dioxide: 2 mol Na: 1 mol Cl 2 3.Multiply ratio by known amount from problem 1.25 mol Cl 2 x 2 mol Na = 2.50 mol Na 1 mol Cl 2 4.Change moles to grams 2.50 mol Na x g Na = g Na 1 mol Na

Mass  Mass  Mass to mass 25.0 g NH 4 NO 3 produces N 2 O and H 2 O when it decomposes. Find the mass of water produced.

1.Start with a balanced equation NH 4 NO 3  N 2 O + 2 H 2 O 2.Change grams to moles 25.0g NH 4 NO 3 x 1 mol NH 4 NO 3 = mol NH 4 NO g NH 4 NO 3 3.Find the mole ratio : 1 mol NH 4 NO 3 : 2 mol H 2 O 4.Multiply ratio by known amount from problem mol NH 4 NO 3 x 2 mol H 2 O = mol H 2 O 1 mol NH 4 NO 3 5.Change moles to grams mol H 2 O x 18.02g H 2 O = 11.2 g H 2 O 1 mol H 2 O

Limiting Reactants  Limiting reactant: the reactant that runs out first  Excess reactant: the reactant that is left over  To solve limiting reactant problems: 1.Work the problem using both reactants and solve the number of moles produced of the same product The one that produces the least amount of moles is the limiting reactant

Percent Yield  Theoretical yield is the maximum amount of product that can be produced (determined through stoichiometric calculations)  Actual yield is the amount produced in lab/from experiment  Percent yield is the ratio of actual to theoretical expressed as a percent. % yield = actual yield x 100 theoretical yield  Reasons for a decrease in percent yield  Loss of products or reactants (spill, stick to side of containers)  Human error  Not all reactants react

Percent Yield continued CH O 2  CO H 2 O  Determine the % yield if 10.0 grams methane burned to produce 19.5 g water. 1.Use stoichiometric calculations to determine theoretical yield of water produced from 10.0 g methane. 2.Using 19.5 g H 2 O as the actual yield, solve for % yield.