Mole Ratios Limiting Reagent % Yield Gas Stoichiometry

Stoichiometry Chemistry is often called the science of proportions; Kitchen Chemistry/Recipes Stoichiometry : the study of chemical quantities based on a balanced equation.

Stoichiometry Measureable and Quantitative relationship between reactants and products So, a chemical reaction takes place: Identify: Classification: Law of Conservation of Mass:

You Must Remember: To BALANCE every equation

Remember the mole?? Quantities in chemical equations are counted as moles.

http://www.chem.uncc.edu/faculty/murphy/1251/slides/C13/img021.JPG

Chemical Ratios Substances in a balanced equation are always in a given proportion to each other. 1N2 + 3H2  2NH3 The proportions can be written as ratios.

Mole Ratios These proportions are called “mole ratios”. 1N2 + 3H2  2NH3 For Every There are/is Creating ratio 1N2 3H2 1mol N2/3mol H2 2NH3 N2

Mole Ratios What is the mole ratio found in the balanced equation below? N2O5  NO2 + O2

The “Given” If 2 moles of N2O5 is reacted, how many moles of NO2 will be formed? There is always a given in a stoichiometry problem that includes A numeric value (2) A metric unit (moles) A substance (N2O5)

Mole-Mole Calculation If 2 moles of N2O5 is reacted, how many moles of NO2 will be formed? 1) 2 mol N2O5 x mole ratio (which one?) 2) 2 mol N2O5 x mol N2O5 (cancel the given) 3) 2 mol N2O5 x mol NO2 (write what you want) mol N2O5

Mole-Mole Calculation 1- Balance the equation 2- Write down your given 3- Use conversion factors to convert moles (use the coefficients here) We call this the Heart of the equation

Heart of Every Equation mol unknown = mol given

Mole-Mole Calculations Coef mol _______________________ mol given coef mol unknown coef mol given

Mole-Mass Problem mol A 1 mol B How much (mass) B can be formed from a given number of moles of A? mol A x mol B x g B = g B mol A 1 mol B 1) The mol-mol ratio comes from the equation 2) The mol-mass ratio comes from the periodic table

C3H8 + 5O2  3CO2 + 4H2O 5.4 moles of propane (C3H8) is converted into how many moles of carbon dioxide?

Mole-Mass Calculations ____________________________________ Molar mass (g) mol given coef mol unknown coef mol given 1 mol

4NH3 + 5O2  6H2O + 4NO How many grams of H2O are produced if 1.9 mol of NH3 are combined with excess oxygen?

Mass-Mole Problem How many moles of B can be formed from a given mass of A? g A x 1 mol A x mol B x = mol B g A mol A 1) The mol-mol ratio comes from the equation 2) The mol-mass ratio comes from the periodic table

Mass-Mole Calculations: mol given 1 mol coef mol unknown __________________________________ molar mass coef mol given (g)

Fe2O3 + 3CO -> 2Fe + 3CO2 How many grams of carbon dioxide are produced with 2 moles of iron (3) oxide?

Mass-Mass Problem How much (mass) B can be formed from a given mass of A? g A x 1 mol A x mol B x g B = g B g A mol A 1 mol B 1) The mol-mol ratio comes from the equation 2) The mol-mass ratio comes from the periodic table

Mass-Mass Calculations: g-given 1 mol coef mol molar mass unknown (g) ____________________________________ molar mass coef mol 1 mol given

Fe2O3 + 3CO -> 2Fe + 3CO2 How many grams of iron would be produced using 25 grams of iron (3) oxide?

Mole Ratios Limiting Reagent-LR % Yield Gas Stoichiometry

Limiting Reagent Limiting reagent = a reactant that limits the amount of product that can be made It can also be thought of as a limiting ingredient

Limiting Reagent Recipe: peanut butter and jelly sandwich 2Br + 3Pb + 2Je  1 Sa 3 ingredients necessary to produce one sandwich Could any one of these run out before the other two?

Excess Reagents Excess = there’s extra of this substance *the substance won’t run out *don’t include this reagent in the calculation If you have 20 loaves of bread, 1 jar of peanut butter and 1 jar of jelly – which ingredient is in excess?

Limiting Reagent To determine the limiting reagent, more than one problem must be done Ex: You have 8 slices of bread and 9 T of peanut butter. Which is the limiting ingredient? (2Br + 3Pb + 2Je  1 Sa) 8 Br x 1Sa = 4 Sa 9 Pb x 1Sa = 3 Sa 2 Br 3Pb

Limiting Reagent The reactant that produces the smallest amount of product is the limiting reagent. 8 Br x 1Sa = 4 Sa 9 Pb x 1Sa = 3 Sa 2 Br 3Pb Limiting reagent Smaller quantity

Uses for Limiting Reactants Nutritional value of food for body Concentration of pollutants

What to do (write these down): Balance equation Convert: 1-have to moles 2-need to moles Compare  have : need One must be > or < ID the LR Excess  compare your have : need

Cu + AgNO3  Cu(NO3)2 + Ag Balance first Know: you have 3.5 grams of Cu and 6 grams of AgNO3. What is the LR and what is excess?

Cu + AgNO3  Cu(NO3)2 + Ag 3.5 grams of Cu / 6 grams of AgNO3

Al + O2  Al2O3 Balance Known: 0.048 mole of powdered Al is placed in a container with 0.030 moles of oxygen. What is the limiting reactant?

Al + O2  Al2O3 0.048 mole Al / 0.030 moles of oxygen

Stoichiometry Ratios and Proportions Mole Ratios Limiting Reagent Yield Gas Stoichiometry

% Yield Theoretical Yield = calculated mass of product Actual Yield = mass of product found in lab Percent Yield = actual yield x 100% theoretical yield

Percent Yield Methanol can be produced through the reaction of CO and H2 in the presence of a catalyst. CO(g) + 2H2(g)  CH3OH(l) If 75.0 g of CO reacts to produce 68.4 g CH3OH, what is the percent yield of CH3OH? 79.8%

% Yield Chlorobenzene, C6H5Cl is used in the production of many important chemicals, such as aspirin, dyes, and disinfectants. C6H6(l) + Cl2(g)  C6H5Cl(s) + HCl(g) When 36.8 g of C6H6 react with an excess of Cl2, the actual yield of C6H5Cl is 38.8 g. What is the percent yield of C6H5Cl? 73.2%

% Yield Aluminum reacts with excess copper (II) sulfate according to the reaction below. If 1.85 g of Al react and the percent yield of Cu is 56.6%, what mass of Cu is produced? Al(s) + CuSO4(aq)  Al2(SO4)3(aq) + Cu(s) 3.70 g

Stoichiometry Ratios and Proportions Mole Ratios Limiting Reagent Yield Gas Stoichiometry

*This volume assumes standard temperature and pressure conditions Molar Volume Molar volume = the space that one mole of ANY gas fills 1 mole = *22.4 liters Remember: 1 L = 1000 mL *This volume assumes standard temperature and pressure conditions

Molar Volume 1) A quantity of gas has a volume of 124.5 cm3.  How many moles of gas are there?

Molar Volume 2) Hydrogen sulfide occupies 278.2cm3. What is the mass of the hydrogen sulfide?

Gas Stoichiometry Instead of counting moles in a reaction, we can also count liters of a gas. 1 liter of N2 reacts with 3 liters of H2 to produce 2 liters of NH3

Gas Stoichiometry What volume of water vapor will be formed when 8.2 L of H2 reacts with excess O2? 2H2 (g) + O2 (g)  2H2O(g) Use a liter-liter ratio!

Gas Stoichiometry What volume of ammonia will form when 52.5 g of nitrogen reacts with excess hydrogen? gN2  mol N2  mol NH3  L NH3 gN2  mol N2  L N2  L NH3

Keep digging! No pun intended