
Concept explainers
Billions of pounds of urea, CO(NH2)2, are produced annually for use as a fertilizer. The principal reaction employed is:
2NH3+ CO2→ CO(NH2)2+ H2O
By assuming unlimited amounts of CO2, how many moles of urea can be produced from each of the following amounts of NH3?
a. 2 mol NH3b. 0.45 mol NH3c. 10 g NH3d. 2.0 kg NH3

Interpretation:
The number of moles of urea is to be determined in the given amounts of NH3.
Concept introduction:
The characteristic mass of a compound is the formula mass of the compound, which is obtained by adding the atomic masses of all atoms.
A conversion factor is a numerical ratio, which is used to change one unit into another.
The chemical formula represents the precise number of atoms in a molecule, but not their structural arrangement.
Answer to Problem 54E
Solution: The number of moles of urea present in the molecules is given as follows:
1 mol urea
0.23 mol urea
0.3 mol urea
59 mol urea
Explanation of Solution
a) 2 mol NH3
The equivalence is obtained between moles of NH3 and moles of urea with the help of the chemical formula as follows:
1 mol urea≡2 mol NH3
In order to obtain the moles of urea, the conversion factor proceeds as follows:
2 mol NH3×1 mol urea2 mol NH3=1 mol urea
Therefore, the number of moles of urea is 1 mol.
b) 0.45 mol NH3
The equivalence is obtained between moles of NH3 and moles of urea with the help of the chemical formula as follows:
1 mol urea≡2 mol NH3
In order to obtain the moles of urea, the conversion factor proceeds as follows:
0.45 mol NH3×1 mol urea2 mol NH3=0.23 mol urea
Therefore, the moles of urea are 0.23 mol.
c) 10 g NH3
The equivalence is obtained between grams of NH3 and moles of NH3 with the help of the chemical formula as follows:
1 mol NH3≡17.03 g NH3
The equivalence is obtained between moles of NH3 and moles of urea with the help of the chemical formula as follows:
1 mol urea≡2 mol NH3
In order to obtain the moles of urea, the conversion factor proceeds as follows:
10 g NH3×1 mol NH317.03 g NH3×1 mol urea2 mol NH3=0.3 mol urea
Here,
molar mass of NH3=17.03 g/mol
Therefore, the moles of urea are 0.3 mol.
d) 2.0 kg NH3
The equivalence is obtained between grams of NH3 and moles of NH3 with the help of the chemical formula as follows:
1 mol NH3≡17.03 g NH3
The equivalence is obtained between moles of NH3 and moles of urea with the help of the chemical formula as follows:
1 mol urea≡2 mol NH3
In order to obtain the moles of urea, the conversion factor proceeds as follows:
2 kg NH3×(1000 g1 kg)×(1 mol NH317.03 g NH3)×(1 mol urea2 mol NH3)=59 mol urea
Here,
molar mass of NH3=17.03 g/mol
Therefore, the moles of urea are 59 mol.
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Chapter 4 Solutions
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