Ok, Need some more help... This is what I have so far.

Question

4. Urea (NH2)2CO is prepared by reacting ammonia with carbon dioxide. The byproduct is water. 637.2g of ammonia are reacted with 787.3 g of carbon dioxide.

molar mass:NH3=17 CO2=44 CO(NH2)2=60.1

a. (10 points) Write a balanced chemical equation.
2NH3+CO2--->CO(NH2)2 +H20
Is this right?
b. (5 points) Determine which of the two reactants (ammonia or carbon dioxide) is a limiting reactant. Show
calculations to support your choice. No credit will be given if your supporting calculations are wrong.
2 moles NH3 is require 1 mole of CO2 to produce one molecule of CO(NH2)2. 2 moles NH3 is 637.2/17=37.5 moles =37.5/2=18.74 moles in 1 NH3?
Available CO2 = 787.3 = 787.3/44=17.89 moles CO2 So since CO2 is smaller, wouldn't it be the limiting agent?

c. (10 points) Which of the two reactants should you use to calculate the theoretical yield (= the maximum amount
possible) of urea? Explain why.
UMMM I would calculate the NH3 because it is the larger one? why? I don't have a clue help?

Answer 1

Ok, Need some more help... This is what I have so far.
4. Urea (NH2)2CO is prepared by reacting ammonia with carbon dioxide. The byproduct is water. 637.2g of ammonia are reacted with 787.3 g of carbon dioxide.

molar mass:NH3=17 CO2=44 CO(NH2)2=60.1

a. (10 points) Write a balanced chemical equation.
2NH3+CO2--->CO(NH2)2 +H20
Is this right?
The equation is right

b. (5 points) Determine which of the two reactants (ammonia or carbon dioxide) is a limiting reactant. Show
calculations to support your choice. No credit will be given if your supporting calculations are wrong.
2 moles NH3 is require 1 mole of CO2 to produce one molecule of CO(NH2)2. 2 moles NH3 is 637.2/17=37.5 moles =37.5/2=18.74 moles in 1 NH3?
Available CO2 = 787.3 = 787.3/44=17.89 moles CO2 So since CO2 is smaller, wouldn't it be the limiting agent?
You have the right answer and your numbers are right; however, there are some misstatements I want to correct.
mols NH3 = 687.3/17 = 37.5 SO IT WILL REQUIRE 37.5/2 = 18.74 MOLS CO2.
mols CO2 available = 787.3/44 = 17.89 so yes, CO2 is the limiting reagent. The part I objected to was "18.74 mols in 1 NH3". The 18.74 mols CO2 is the mols CO2 that will be required to react with all of the NH3 and since that is higher than the mols CO2 you have (17.89), then CO2 is the limiting reagent.

c. (10 points) Which of the two reactants should you use to calculate the theoretical yield (= the maximum amount
possible) of urea? Explain why.
UMMM I would calculate the NH3 because it is the larger one? why? I don't have a clue help?
You want to use the smaller one because that is what is determining how much urea you can obtain. The NH3 doesn't determine that since it is not the limiting reagent. The CO2 is the limiting reagent and it is the one that determines how much urea you get. Said another way the amount of urea you obtain is determined by the mols CO2 you have so that is the maximum amount of urea that can be obtained under the circumstances.
Let me show you how that works.
If you use NH3 the mols NH3 = 37.5 so you can produce 37.5/2 = 18.7 or mols urea. How many grams is that? 18.7 x 60.1 = about 1126 g urea.
Now, using CO2, there are 17.89 mols CO2 and you can get 17.89 mols urea. That is 17.89 x 60.1 = about 1075g. So one reactant (the NH3) will produce 1126 g urea if ALL OF IT REACTS with an unlimited amount of CO2. You can get 1075 g urea if you use ALL OF THE CO2 and an unlimited supply of NH3. So how much can you get if you use them together. No more than the smaller amount will produce.