Presentation on theme: "Stoichiometry Chemistry Ms. Piela. Stoichiometry The quantitative study of reactants and products in a chemical reaction ▫Chemical reactions give info."— Presentation transcript:
Stoichiometry The quantitative study of reactants and products in a chemical reaction ▫Chemical reactions give info about how molecules combine, and can be used to determine amounts of substances that form
Mole to Mole Calculations When using a chemical equation to determine the amount of the substance, you must relate them by their mole ratios Example #1: ____ H 2 + ____ O 2 → ____ H 2 O If you start with 4 moles of O 2 how many moles of H 2 O would form?
Mole to Mole Calculations Example #2: ___ Fe + ____ S → ___Fe 2 S 3 How many moles of iron (III) sulfide, Fe 2 S 3, forms if the reaction initially starts with 8 moles of iron, Fe?
Mass to Mass Calculations Example #1: ___ H 2 + ___ O 2 → ___ H 2 O If 2.4 g of O 2 are reacted with excess H 2 gas, how many moles of H 2 O would form? 0.15 mol H 2 O
Mass to Mass Calculations Example #2: ___ H 2 + ___ O 2 → ___ H 2 O In the above equation, if I started with 3 grams of H 2, how many grams of H 2 O would form? 26.8 g H 2 O
Mass to Mass Calculations Example #3: _ NH 3 (g) + _ CO 2 (g) → _ (NH 2 ) 2 CO (aq) + _H 2 O (l) When 2.00 grams of ammonia, NH 3, react with excess CO 2, what mass of water (in grams) is formed? 1.06 g H 2 O
Limiting Reactant The reactant used up first in a chemical reaction ▫Also called limiting reagent After a reaction, excess reactants are left ▫These are reactants present in greater quantities that remain after a reaction takes place
Limiting Reactant Chair analogy: It’s your lucky day! Mr. Nelson has hired you to make chairs! The chairs follow the “reaction”: 4 legs + 1 seat + 10 screws → 1 chair Here are the supplies you have: 10 legs, 5 seats, and 100 screws. How many chairs be made? What is the limiting reactant?
Limiting Reactant The limiting reactant can be found by determining which of the starting amounts yields the least amount of product
Limiting Reactant Example Problem ▫Sodium chloride can be prepared by the reaction of sodium with chlorine gas: 2Na (s) + Cl 2 (g) 2NaCl (s) ▫Suppose that 6.70 mol Na reacts with 3.2 mol Cl 2 How many moles of NaCl will be formed in this reaction? What is the limiting reactant? Cl 2 6.4 mol NaCl
Limiting Reactant Practice Problem 2.70 mol C 2 H 4 is reacted with 6.30 mol of O 2. Calculate the amount in moles of water that forms, and identify the limiting reactant. C 2 H 4 (g) + 3O 2 (g) 2CO 2 (g) + 2H 2 O (g) 4.2 mol H 2 O
Limiting Reactant Example Problem Urea is prepared by reacting ammonia with carbon dioxide: 2 NH 3 (g) + CO 2 (g) → (NH 2 ) 2 CO (aq) + H 2 O (l) In one process, 637.2 g of NH 3 are treated with 1142 g of CO 2. Calculate the mass of urea, (NH 2 ) 2 CO, formed. 1122 g urea
Limiting Reactant Practice Problem Calculate the number of grams of NH 3 produced by the reaction of 5.40 g of hydrogen with 8.25 g of nitrogen. The balanced equation is: N 2 + 3 H 2 2 NH 3 9.97 g NH 3
Percent Yield Theoretical yield is the amount of product that would result if all the limiting reagent reacted Actual yield is the amount actually obtained in lab from a reaction ▫Actual yield is almost always less than theoretical
Percent Yield Percent yield describes proportion of actual yield to theoretical yield.
Percent Yield Example Problem When 84.8 g of iron (III) oxide reacts with an excess of carbon monoxide, 54.3 g of iron is produced. What is the percent yield of this reaction? Fe 2 O 3 (s) + 3CO (g) 2 Fe (s) + 3CO 2 (g) 91.6%
Percent Yield Practice Problem If 25 grams of carbon dioxide gas can be produced in the following reaction, how many grams of sodium hydroxide should be produced? If 10.7 grams of sodium hydroxide are actually produced, what is the percent yield? NaHCO 3 NaOH + CO 2 22.7 g NaOH / 41.1%