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.
a. (15 points) Which of the two reactants is a limiting reactant? Show your calculations (including the correctly
balanced chemical equation) to explain your choice.
Balanced Chemical Equation:
Calculations:
Explanation and conclusion:
b. (10 points) Which of the two reactants should you use to calculate the theoretical yield (= the maximum amount
possible)? Explain why.
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.
a. To determine the limiting reactant, we need to compare the amount of product that can be formed from each reactant based on their stoichiometry.
The balanced chemical equation for the reaction is:
2NH3 + CO2 → (NH2)2CO + H2O
First, let's calculate the number of moles for both reactants:
Molar mass of ammonia (NH3): 14.01 g/mol
Molar mass of carbon dioxide (CO2): 44.01 g/mol
Number of moles of ammonia (NH3):
637.2 g / 14.01 g/mol ≈ 45.5 mol
Number of moles of carbon dioxide (CO2):
787.3 g / 44.01 g/mol ≈ 17.9 mol
Now, let's determine the stoichiometric ratio between the reactants and the product:
From the balanced chemical equation, we know that 2 moles of ammonia react with 1 mole of carbon dioxide to produce 1 mole of urea.
Stoichiometric ratio between ammonia and carbon dioxide:
2 mol NH3 : 1 mol CO2
Based on this ratio, we can calculate the amount of ammonia required to react with all the carbon dioxide:
Calculating the required amount of ammonia:
1 mol CO2 × (2 mol NH3 / 1 mol CO2) = 2 mol NH3
Since 1 mole of carbon dioxide requires 2 moles of ammonia, and we have 45.5 moles of ammonia available, it means that there is excess ammonia. Therefore, ammonia is not the limiting reactant.
However, to determine if there is excess carbon dioxide or if it is the limiting reactant, we need to calculate the amount of urea that can be formed from 17.9 moles of carbon dioxide:
Calculating the theoretical yield of urea from carbon dioxide:
17.9 mol CO2 × (1 mol (NH2)2CO / 1 mol CO2) = 17.9 mol (NH2)2CO
So, based on the stoichiometry, we can conclude that 17.9 moles of carbon dioxide would produce 17.9 moles of urea.
To determine the limiting reactant, we compare the number of moles actually available for each reactant in relation to the stoichiometric amounts. Since we have 45.5 moles of ammonia, which is more than the required 17.9 moles, and only 17.9 moles of carbon dioxide, which is exactly the required amount, we can conclude that carbon dioxide is the limiting reactant.
b. The theoretical yield, which is the maximum amount of product that can be formed, will be determined by the limiting reactant. In this case, since carbon dioxide is the limiting reactant, we should use its amount to calculate the theoretical yield. The theoretical yield will be 17.9 moles of urea, which can be converted to grams using the molar mass of urea (60.06 g/mol) if desired.