Question about Problem 31 on Limiting Reactant Calculations Module

[Chiara Frank]

Hey guys! In the Limiting Reactions Calculations Module, problem 31 uses the balanced equation 2A + 1B --> 3C, and provides the information that 1 mol B reacts with 2 mol A, but there is only 1 mol A present, so it is the limiting reagent. It then asks, how much of B would be used? Considering the reactants, that 2 mol of A would require 1 mol of B, and there is only 1 present, I divided it the mol of B by 2 to get 0.5, thus that 0.5 mol of B would be used. However, I was not sure if there is a formula to calculate the amount used rather than just looking at the ratio in the equation? Thanks!

[joshua_quinn_1C]

In order to calculate this, you would use the amount of limiting reactant which in this case is 1 mole of A and then use the mole ratio of 2:1 to convert it to B which would give you the answer you got of 0.5 mole of B. In other words, using the mole ratio is a sufficient way to calculate how many moles of a certain substance would be used based on a limiting reactant.

[RJ Mathews 1K]

I also use the molar ratios to calculate the limiting reactants and reagents used. I was concerned about how this might "scale" as the questions get harder, but considering that this is what was covered in the attached video, I think this might be the "right" way to do it haha. With my limited knowledge, I also have no idea how balancing equations can get much harder :) I just hope it doesn't

[Vincent Nguyen 3G]

The closest thing to a formula for determining how many moles will be used would be the mole ratio like mentioned above. If you want to really make it feel like a formula, then you can try writing out the mole ratio as a fraction (like 2A/1B) and then multiplying the whole thing by (0.5/0.5) to get (1A/0.5B). This setup makes it look like unit conversion and also decreases chances of making a mistake.