STOICHIOMETRY Limiting Reactant Problems
Limiting Reactant You work in a bakery and your boss says that she wants you to bake as many cakes as you can. You have a 100 pound bag of sugar and a 100 pound bag of flour. Which ingredient will you run out of first? What if you knew that one cake requires 245 g of sugar and 283 g of flour. Which ingredient will you run out of first? Flour That is going tolimitthe number of cakes you can make. Will you have sugar left over? it will be the excess reactant
Limiting Reactant You have a brand new jar of peanut butter and a new jar of grape jelly and 9 slices of bread. How many of my son’s favorite sandwiches can you make? 4.5 What limits the number of sandwiches? The slices of bread Bread is the limiting reactant. Peanut butter and jelly are both in excess.
A limiting reactant is the reactant that limits the amount of the other reactants that can combine, and the amount of products formed in a chemical reaction. The excess reactant is the substance that is not used up completely in a reaction.
Limiting Reactant Other examples: Four hundred people want to take a flight. The plane has only 350 seats available. Only 350 people can go on the flight. The number of seats on the airplane limits the number of people that can travel. There are 50 people in excess.
Limiting Reactant A Few Days ago, Caleb was going to pass out Valentine cards. He went through his valentines and discarded the ones that didn’t have Sponge Bob or Dora the Explorer on them. He now had only 12 acceptable valentines. He knows he would get a kiss from each girl that received an acceptable valentine. His classed had 15 girls. Limiting reactant: acceptable valentines Excess reactant: girls The product: The KISSES are limited to 12
Limiting Reactant How about the game of musical Chairs?? : the limiting reactant is the chairs the players are in excess.
Limiting Reactant Real LifeHow many times do you breathe in one minute? Let’s count. Did you know that the average person exhales 20 moles of carbon dioxide in a day. How many grams is this? 20 moles CO2 | 44.01 g CO2 = 880 g CO2 1 | 1 mol CO2
Limiting Reactant Do we ever need to worry about the amount of CO2 that we exhale? Why not? What if we were in a contained atmosphere? Prolonged exposure of humans to concentrations of 5 % CO2 may cause unconsciousness and death. How do we remove CO2 from the air? React it with lithium hydroxide.
2 LiOH + CO2 Li2CO3↓ + H2O How much LiOH is needed to remove the CO2 from the atmosphere for one person for one day? Given: 20 moles CO2 Unknown: grams of LiOH 20 moles CO2 | 2 mole LiOH | 23.949 g LiOH = 960 grams LiOH 1 | 1 mole CO2 | 1 mole LiOH Who might need this information? Astronauts Launch
Apollo 13 space flight there were two compartments in the capsule, the service station compartment blew up and the 3 astronauts had to remain in the Lunar Module. Carbon dioxide levels were rising. The Big Question, Did they have enough LiOH to absorb the carbon dioxide produced by 3 people? On the Lunar Module there were only “5 filters to last 2 people for 1.5 days” How much LiOH does 1 filter contain? 1 filter | 2 people | 960 g LiOH | 1.5 days = 576 grams LiOH 1 | 5 filters | 1 person So LiOH would have been the limiting reactant and CO2 would have been the excess reactant.
Practice Problems Consider the reaction I2O5(g) + 5 CO(g) -------> 5 CO2(g) + I2(g) a) If 80.0 grams I2O5, reacts with 28.0 grams of CO.Determine the mass of iodine I2, that is produced? b) If, in the above situation, only 0.160 moles, of iodine, I2 was produced.i) what mass of iodine was produced?ii) what would be the % yield of iodine?
Practice Problems Zinc and sulfur react to form zinc sulfide according to the equation. Zn + S ZnS If 25.0 g of zinc and 30.0 g of sulfur are mixed, a) Which chemical is the limiting reactant? b) How many grams of ZnS will be formed? c) How many grams of the excess reactant will remain after the reaction is over?
Practice Problems Which element is in excess when 3.00 grams of Mg is ignited in 2.20 grams of pure oxygen? What mass is in excess? What mass of MgO is formed?