Using a limiting reagent is just as simple as finding one.
Lets Use a Sample Problem with Using Limiting Reagents, where I will lay out the steps for how you should do a problem.
Example. If 53.6 grams of CH5N were reacted with 87.9 grams of O2, how many grams of CO2 would be produced?
4C5N + 11O2 --> 4CO2 + 10H2O + 4NO
Step 1: Find the limiting reagent
CH5N - 53.6 grams O2 - 87.9 grams
GFW = 12 + 5 (1) + 14 = 31 GFW = 32
# moles = 53.6/31 # moles = 87.9/32
# moles = 1.73 # moles = 2.75 (LR)
From this, you should compare these answers to the ratios and see which one you need MORE of. As discussed that is the limiting reagent and in this case, O2 is the limiting reagent. (LR) stands for/represents limiting reagent.
Step 2: Multiply the number of moles of the limiting reagent by the ratio of the product to the limiting reagent to find the number of moles of the product. Here, since the question asks how many grams of CO2 is produced, we can determine that CO2 is the product.
So, it would be 2.75 x 4/11 = 1
Step 3: use the formula # moles = grams/GFW for the product (in this case CO2)
GFW of CO2 = 12 + 2 (16) = 44
# moles = grams/GFW
1 = g/44
Answer: CO2 would have produced 44 grams.
Now, head to our worksheet on using limiting reagents and embark on the unforgettable journet