Stoichiometry Chapter 11

11.1 Stoichiometry Stoichiometry is the study of quantitative relationships between the amounts of reactants used and amounts of products formed by a chemical reaction. Stoichiometry is the study of quantitative relationships between the amounts of reactants used and amounts of products formed by a chemical reaction. – –2 slices of bread + 1 slice of ham  1 ham sandwich How do you figure out a chemical equation’s recipe? How do you figure out a chemical equation’s recipe? N 2 + 3H 2  2NH 3 This 1:3:2 ratio can symbolize numbers of molecules or moles.

Mole Relationships Mole Ratio: a ratio between the numbers of moles of any two of the substances in a balanced chemical equation. Mole Ratio: a ratio between the numbers of moles of any two of the substances in a balanced chemical equation. What are all of the possible mole ratios in the equation? What are all of the possible mole ratios in the equation? –4Al(s) + 3O 2 (g) → 2Al 2 O 3 (s)

Mole/Mole Stoichiometry Moles of known x mole ratio = moles of unknown Moles of known x mole ratio = moles of unknown substancesubstance substancesubstance –Mole ratio = moles of unknown (coefficient) moles of known (coefficient) moles of known (coefficient) 2 slices of bread + 1 slice of ham  1 ham sandwich If you have 10 slices of bread how many slices of ham are needed?

Mole/Mole Stoichiometry Find the quantities of reactants and products in chemical reactions Find the quantities of reactants and products in chemical reactions Use the mole ratio to convert what you have to what you want to find Use the mole ratio to convert what you have to what you want to find

Mole/Mole Stoichiometry How many moles of aluminum are needed to form 3.7 moles of aluminum oxide? How many moles of aluminum are needed to form 3.7 moles of aluminum oxide? ____Al + ____O 2 → ____Al 2 O 3 How many moles of Al 2 O 3 are formed when 0.78 moles of O 2 reacts with aluminum? How many moles of Al 2 O 3 are formed when 0.78 moles of O 2 reacts with aluminum?

11.2 Calculations Moles to Mass Given the number of moles of a reactant or product, we can calculate the mass of another reactant or product. Given the number of moles of a reactant or product, we can calculate the mass of another reactant or product. Use the mole ratio to convert from what you have to what you want to find. Use the mole ratio to convert from what you have to what you want to find. Use the molar mass of what you want to find to convert from moles to grams. Use the molar mass of what you want to find to convert from moles to grams.

Moles to Mass Practice If 0.25 moles of TiO 2 are used, how many grams of Cl 2 are needed? 1TiO 2 + 1C + 2Cl 2  1TiCl 4 + CO 2

Mole to mass If 2.50 moles of NaCl are used, how many grams of Cl 2 are produced? 2NaCl  2Na + 1Cl 2

Mass to Mass Given the number of grams of a reactant or product, we can calculate the number of grams of another reactant or product. Given the number of grams of a reactant or product, we can calculate the number of grams of another reactant or product. Use molar mass of what you have to convert it to moles. Use molar mass of what you have to convert it to moles. The rest of the process is the same: The rest of the process is the same: –Use mole ratio to convert from what you have to what you need find. –Use molar mass of what you need find to convert your answer from moles to grams.

Mass to Mass Practice 2NaN 3  2Na + 3N g ? g g ? g 2SO O 2 + 2H 2 O  2H 2 SO g ? g 2.50 g ? g

Volume and Particle Relationships How many molecules of oxygen are produced by the decomposition of 6.54g of potassium chlorate? How many molecules of oxygen are produced by the decomposition of 6.54g of potassium chlorate? How many liters of oxygen are required to burn 3.86L of carbon monoxide? How many liters of oxygen are required to burn 3.86L of carbon monoxide?

Mass Relationships must obey the law of conservation of mass (moles aren’t equal, but mass must be the same on both sides) must obey the law of conservation of mass (moles aren’t equal, but mass must be the same on both sides) What mass of oxygen, O 2, is required to completely combust 454 g of propane, C 3 H 8 ? What masses of CO 2 and H 2 O are produced? What mass of oxygen, O 2, is required to completely combust 454 g of propane, C 3 H 8 ? What masses of CO 2 and H 2 O are produced? C 3 H 8 + 5O 2  3CO 2 + 4H 2 O

More Mass Practice… CaC 2 + 2H 2 O  C 2 H 2 + Ca(OH) 2 CaC 2 + 2H 2 O  C 2 H 2 + Ca(OH) 2 How many grams of C 2 H 2 are produced by adding water to 5.00g CaC 2 ? How many grams of C 2 H 2 are produced by adding water to 5.00g CaC 2 ? How many moles of CaC 2 are needed to react completely with 49.0g H 2 O? How many moles of CaC 2 are needed to react completely with 49.0g H 2 O?

11.3 Limiting Reactants A limiting reactant determines the amount of product formed. A limiting reactant determines the amount of product formed. –1. Start with a balanced chemical equation. –2. Identify what you have for each reactant. –3. Convert what you have to moles. –4. Calculate the ratio of available moles of each reactant. (what you have) –5. Use the balanced chemical equation to calculate the ratio of moles of each reactant (what you need) –6. For each reactant, do you have more or less than what you need?

Limiting Reactant 1. 6Na + 1Fe 2 O 3  3Na 2 O + 2Fe g g We have 6.94 mol Na; we need 6 mol. Na is in excess. We have 1 mol Fe 2 O 3 ; we need 1 mol. Fe 2 O 3 will run out first.

Limiting Reactants C 2 H 4 +3O 2  2CO 2 + 2H 2 O C 2 H 4 +3O 2  2CO 2 + 2H 2 O If 2.70mol C 2 H 4 is reacted with 6.30 mol O 2 ; identify the limiting reactant. If 2.70mol C 2 H 4 is reacted with 6.30 mol O 2 ; identify the limiting reactant. Identify the limiting reactant if 2.70 mol C 2 H 4 is reacted with 6.30 mol O 2. Identify the limiting reactant if 2.70 mol C 2 H 4 is reacted with 6.30 mol O 2.

Limiting Reactants Pure silicon, required for computer chips and solar cells, is made by the reaction Pure silicon, required for computer chips and solar cells, is made by the reaction SiCl 4 + 2Mg  Si + 2MgCl 2 If you begin with 225 g each of SiCl 4 and Mg, which is the limiting reactant in this reaction? What quantity of Si, in grams, can be produced?

11.4 Percent Yield The ratio of the actual yield (formed in lab) to the theoretical yield (max amount that could be formed) The ratio of the actual yield (formed in lab) to the theoretical yield (max amount that could be formed)

Percent Yield When 84.8g of iron (III) oxide reacts with an excess of carbon monoxide, 54.3g of iron is produced. What is the percent yield? When 84.8g of iron (III) oxide reacts with an excess of carbon monoxide, 54.3g of iron is produced. What is the percent yield?

Percent Yield Methanol, CH 3 OH, can be burned in oxygen to provide energy, or it can be decomposed to form hydrogen gas, which can then be used as a fuel. CH 3 OH  2H 2 + CO If 125 g of methanol is decomposed, what is the theoretical yield of hydrogen? If only 13.6 g of hydrogen is obtained, what is the percent yield of the gas?