Question 4.14: Stoichiometry When urea, (NH2)2CO, is acted on by the enzyme...
Stoichiometry
When urea, {(\text{NH}_{2})_{2}}\text{CO}, is acted on by the enzyme urease in the presence of water, ammonia and carbon dioxide are produced. Urease, the catalyst, is placed over the reaction arrow.
If excess water is present (more than necessary for the reaction), how many grams each of \text{CO}_{2} and \text{NH}_{3} are produced from 0.83 mol of urea?
Strategy
We are given moles of urea and asked for grams of \text{CO}_{2}. First, we use the conversion factor 1 mol urea = 1 mol \text{CO}_{2} to find the number of moles of \text{CO}_{2} that will be produced and then convert moles of \text{CO}_{2} to grams of \text{CO}_{2}. We use the same strategy to find the number of grams of \text{NH}_{3} produced.
For grams of \pmb{\text{CO}_{2}}:
Step 1: We first convert moles of urea to moles of carbon dioxide using the conversion factor derived from the balanced chemical equation, 1 mol urea = 1 mol carbon dioxide.
Step 2: Use the conversion factor 1 mol \text{CO}_{2} = 44 g \text{CO}_{2} and then do the math to give the answer:
0.83 \ \cancel{\text{mol urea}} \times \frac{1\ \cancel{\text{mol CO}_{2}}}{1\ \cancel{\text{mol urea}}} \times \frac{17\ \text{g CO}_{2}}{1\ \cancel{\text{mol CO}_{2}}} = 28\ \text{g CO}_{2}For grams of \pmb{\text{NH}_{3}}:
Steps 1 and 2 combine into one equation, where we follow the same procedure as for \text{CO}_{2} but use different conversion factors:
■ Quick Check 4.14
Ethanol is produced industrially by the reaction of ethylene with water in the presence of an acid catalyst. How many grams of ethanol are produced from 7.24 mol of ethylene? Assume that excess water is present.