2 StoichiometryThe study of quantifiable (measurable) ratios/relationships that exist in chemical formulas and reactions.In many ways, stoichiometry is the backbone of the most practical part of chemistry; it helps us relate actual quantities (measured by mass or volume) of reactants to products in a chemical reaction.
3 Stoichiometry – a lot like baking cookies! You have to put the ingredients together in the proper proportions to make a cookie that tastes good!Consider the following balanced equation:2Na + Cl2 2NaCl
4 Consider the following balanced equation: 2Na + Cl2 2NaCl We can look at this equation two different ways:1. at the atomic/molecular scale: 2 Na atoms react with 1 Chlorine molecule to produce 2 formula units of NaCl2. at the real-world, measurable scale: 2 mol of Na react with 1 mol of Cl2 to produce 2 mol of NaCl (you could measure out those amounts)
5 Dimensional AnalysisCan be used to relate the moles of reactants and products in a chemical reaction to one another.It is essentially a matter of determining the ratio of reactants and products by looking at the coefficients in the balanced chemical equation. In the reaction above, the ratio of sodium to chlorine is 2:1The ratio of sodium to sodium chloride is 2 Na:2 NaClThe ratio of chlorine to sodium chloride is 1 Cl2:2 NaCl
6 Dimensional AnalysisIf you’re starting out with moles of sodium and you want to know how many moles of chlorine you need to fully react with the sodium, you can use dimensional analysis:0.650 mol Na x 1 mol Cl2= Mol Cl22 mol NaMole Ratio
7 Dimensional AnalysisIf you want to produce 6.4 moles of sodium chloride, how many moles of chlorine do you need to use?6.4 mol NaCl x 1 mol Cl2 = 3.2 mol Cl22 mol NaClBecause we can literally measure out the moles of sodium by weighing it (1 mol = g) and we can literally measure out the moles of chlorine by volume (1 mol = 22.4 L), we can literally put the reactants together in the proper proportions.Mole Ratio
8 When solving a stoichiometry problem… You’ll always be given a quantity of either a product or reactant that you have to relate to a quantity of another product or reactant.To do this, you’ll use the balanced chemical equation as well as the mole equivalencies you’ve been using in mole conversions.
9 These equivalencies are: 1 mole = 6.02 x 1023 particles(molecules, formula units, atoms, etc.)1 mole = 22.4 L of gas at STP(Standard Temperature 0° C & Pressure 1 atm)1 mole = mass in grams(from periodic table, add masses of elements for compounds)
10 The equivalencies (conversion factors) you’ll use depend on the specific problem, but the logic is always the same:quantity of unknown (measurable)Quantity of given (measurable)moles of givenmoles of unknown
11 New and Improved Mole Map! moles of substance Bmoles of substance Aliters of substance Bparticles of substance Agrams of substance Aliters of substance Aparticles of substance Bgrams of substance BThis is your Mole Ratio (from balanced eq’n)
12 Given the following equation: CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l)What mass of oxygen will react with 36.0 g of methane?Plan: grams CH4 mol CH4 mol O2 grams O2Calculations:36.0 g CH4 x 1 mol CH4 x 2 mol O2 x g O2 = g O2 = 144 g O216.04 g CH4 1 mol CH mol O2
13 Given the following equation: CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l)What mass of water would be produced when oxygen reacts with 36.0 g of methane?Plan: grams CH4 mol CH4 mol H2O grams H2OCalculations:36.0 g CH4 x 1 mol CH4 x 2 mol H2O x g H2O = 80.9 g H2O16.04 g CH4 1 mol CH mol H2O
14 Given the following equation: CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l)How many Liters of carbon dioxide would be produced from the reaction if 44.0 g of oxygen are consumed?Plan: grams O2 mol O2 mol CO2 L CO2Calculations:44.0 g O2 x 1 mol O2 x 1 mol CO2 x L CO2 = ?? L CO2g O2 2 mol O mol CO2