What is the largest number of SO3 molecules

[foleyt70]

okay. i have a test in chemistry tomorrow and I've been studying forever but I am really having trouble with some problems on the study guide. for example, one of the problems is 1) consider the reaction
Mg(s)+I2(s)---->MgI2(s) Under which of the following reaction conditions will Mg be the limiting reagent?

how would i go to do that? i know the answer is a) 200 atoms of Mg and 300 molecules of I2 and B) .16 mol Mg and .25 mol I2 but only because someone told me

2) Consider the reaction
2 SO2 + 02 ---> 2SO3
What is the largest number of SO3 molecules which could be made from 381 SO2 molecules and 185 O2 molecules?

 

[rocomath]

Both of these questions are the same, just use your starting material and find out how much of the product you will form. The one that forms the least is the Limiting reagent.

Also, for question 1. Are you given actual starting material?

 

[foleyt70]

no for question one you aren't given actual starting material.. but like for question 2, how do you get molecules to like grams? or do i not have to?