I have two questions:

Question

1. A sample of 10.7 g of CO reacts completely with O2 to form CO2. How many grams of CO2 will be formed?

2. Urea (NH2)2CO is prepared by reacting ammonia with carbon dioxide. The byproduct is water. 637.2 g of ammonia are reacted with 787.3 g of carbon dioxide. Which of the two reactants is a limiting reactant.

*My textbook is useless and this is an online class with no lecture. I am supposed to show my work and use the correct number of significant figures. I've been working on this assignment for hours and have hit a wall! Thanks!

Answer 1

#1 is a simple (simple means it isn't a limiting reagent problem) stoichiometry problem. Here is a worked example. Just follow the steps.
http://www.jiskha.com/science/chemistry/stoichiometry.html
Post your work if you get stuck.

#2. #2 is a limiting regent problem. The way I solve these is to solve TWO simple stoichiometry problems as in # 1 above. Solve the first one with 637.2 g NH3 to produce H2O and solve the second time with 787.3 g CO2 to produce water. The moles you form from each "problem" will not be the same; the correct answer in limiting reagent problems is ALWAYS the smaller one and the regent producing that value is the limiting reagent.
Post your work if you get stuck.

Answer 2

Hi Dr. Bob,

Thank you for the help! I took a few hours to think about something else and I was finally able to get the problems answered. I hope I did my calculations correctly.

Thanks again!

Answer 3

You're quite welcome.