Model 4: Using Moles of Limiting Reagent in Stoichiometry The above pictures are

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Model 4: Using Moles of Limiting Reagent in Stoichiometry The above pictures are not realistic because they involve so very few molecules. In a "real-world" sampl you are likely to have on the order of 10" molecules. Consider the following: Suppose you have a reaction vessel initially containing 13.5 moles of sulfur dioxide and 11.2 moles of oxygen. mol SO2 required to react with all o, - 11.2 mol o, x 2 mol SO2 1 mol O2 - 22.4 mol So Since there aren't 22.4 moles of sulfur dioxide available, we conclude that sulfur dioxide is the limiting reagent and oxygen is the reagent in excess. The numbers of moles of sulfur trioxide and left over ox when the reaction is complete are: ygen mol SO, produced - 13.5 mol So, 2 mol s0, mol Or consumed - 13.5 mol So, x 1 mol 06.75 mol o mol O2 remaining 11.2 mol O initially-6.75 mol O2 consumed - 4.45 mol o 13.5 mol SOs 2 mol SO2 2 mol SO Key Questions 3a. (Circle the correct answer.) It is the number of moles of the excess reagent or limiting reagent that is used to determine how many moles of each product is produced? b. Write in your own words how one determines the amount of excess reagent that remains unreacted after a reaction is complete. (What is the starting point for calculations? What conversion factors are used? What calculation is necessary to finish the determination?)

Explanation / Answer

a. Limiting reagent defines the extent of the reaction.

b. By knowing the stoichiometry of the reaction and no. of moles of limiting and excess reagent, we can find the amount of excess reagent left to us.

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