Question

Determine the percent yield for this reaction.?

2NH₃+CO₂ --> CN₂H₄O + H₂O

50.0g of ammonia reacted with 50.0g of carbon dioxide and 60.0g of urea was obtained.

I calculate the ammount of NH₃ and CO₂ in moles which I get 0.3408 and 0.8802 respectively. Then I determine which is the limiting reactant which is NH₃. (0.1704 mol CO₂ is required to react with all of the NH₃ and 1.7604 mol NH₃ is required to react with all of the CO₂). Then I calculate the theoretical yield and get 0.1704mol which is 10.24g of CN₂H₄O which is less than 60.07. What I did wrong? Thank you in advance :)

Answer 1

See below.

Explanation:

Step 1: Calculate the number of moles of each reactant.

`"50.0 grams" NH_3 * (("1 mole" NH_3)/("17.031 grams"))="2.94 moles" NH_3`

`"50.0 grams" CO_2 * (("1 mole" CO_2)/("44.009 grams"))="1.14 moles" CO_2`

Step 2: Identify the limiting reagent.

We need 2 moles of `NH_3` for every 1 mole of `CO_2`, so to check to see if we have enough `NH_3` we will multiply the moles of `CO_2` by 2:

`1.14*2="2.28 moles of ammonia needed"`

We have more than enough ammonia for the amount of `CO_2` we have, so `CO_2` is therefore our limiting reagent.

Step 3: Calculate how much `CN_2H_4O` `"1.14 moles"` of `CO_2` will make by using the mole ratio between `CO_2` and `CN_2H_4O`

`"1.14 moles" CO_2*(("1 mole" CN_2H_4O)/("1 mole" CO_2))="1.14 moles" CN_2H_4O`

Since there is a 1:1 ratio between how many moles of `CO_2` we have and how many moles of `CN_2H_4O` will be produced, the product's moles will same number of moles of `CO_2`.

If for instance, 1 mole of `CO_2` produced 2 moles of product, we would have twice the moles of product as the moles of `CO_2`.

Step 4: Convert moles to grams.

`"1.14 moles" CN_2H_4O*(("60.056 grams")/("1 mole" CN_2H_4O))="68.5 grams" CN_2H_4O`

This number is our theoretical yield in grams.

Step 5: Determine percent yield.

The equation for percent yield is:

`"% yield"=("actual yield"/"theoretical yield")*100`

We have all of the numbers necessary, so we can plug in:

`"% yield"=("60.0 grams"/"68.5 grams")*100=87.6%`

I hope this helps!