Explain what a limiting reactant is and describe the process to determine the limiting reactant in the example below:

Question

Given 3.4 grams of x element with a molar mass of 24 g/mol and 4.2 grams of y element with a molar mass of 35 g/mol. How much of compound xy2 can be generated?

Answer 1

A limiting reactant is the reactant in a chemical reaction that will run out first and therefore will determine how much product can be formed. It's analogous to having 6 hot dogs and 8 hot dog buns. The limiting reactant in this case is the 6 hot dogs since they will run out before the buns and the total amount of product you can make is 6 sandwiches (not 8). The buns will be in excess.

There are different ways to identify the limiting reactant. The process I use is to simply divide the moles of each reactant by the coefficient in the balanced equation, as follows:

X + 2Y ==> XY₂ ... BALANCED EQUATION

moles X = 3.4 g x 1 mol / 24 g = 0.14 mols X

moles Y = 4.2 g x 1 mol / 35 g = 0.12 mols Y

Dividing mols by coefficient in balanced equation we have ...

0.14 X / 1 = 0.14

0.12 Y / 2 = 0.06

Since 0.06 is less than 0.14 Y is the limiting reactant

How much XY can be generated?

0.12 mols Y x 1 mol XY2 / 2 mols Y = 0.06 mols XY