Comparing Calculated Moles to Required

[Brandon Ignacio 2J]

I had a general question about the end of process of finding the limiting reactant. Once we find the amount of moles required for each of our reactants, why do we multiply the required moles of one reactant by the stoichiometric coefficient of the other reactant? For example, in the audio visual topic on limiting reactant calculations, Dr. Lavelle multiplied the 1.56 mol of CaC2 required by 2 and said that 1.56 mol requires 3.12 mol of H2O. Why isn't it the calculated moles of H2O that are multiplied by 2? I'm having trouble understanding this conceptually as I feel like I would naturally multiply it by its own coefficient to find how many moles are required in the reaction.

[Steven Tjandra 1B]

Hey there,

Interesting question, it's true that chemistry can sometimes feel very unintuitive with all the random numbers being tossed around. If we think about what stoichiometric coefficients are they are the ratio of compounds/atoms you need to make something. Just like a recipe. So if I were to say that to make one sandwich I needed one piece of cheese and two slices of bread I can represent that as Cheese + 2Bread -> Sandwich!

If I wanted to figure out how many sandwiches I could make, I wouldn't take the bread I have and multiply by 2, I would divide by 2 since each sandwich needs two pieces of bread. I wouldn't multiply the cheese by anything since one cheese goes in each sandwich. So, in the end if I had 3 cheese and five bread I would know I can make 3 sandwiches with the 3 cheese I have and 2.5 sandwiches with the 5 bread I have. So in the end, the bread is the limiting reagent since it runs out quicker.

Hungry,
Steven Tjandra