2X + 3Y --> X2Y3
You have initially 4 moles of both X and Y.
2 moles of X and 3 moles of Y are needed to make X2Y3.
4 moles X * (3 moles Y/2 moles X) = 6 moles Y
We do not have 6 moles of y, which means that Y is the limiting reactant.
4 moles Y * (2 moles X/3 moles Y) = 2.667 moles X
We start off with 4 moles of X, and we react 2.667 moles of X.
We start off with 4 moles of Y, and we react all 4 moles of Y. (Remember, this is the limiting reactant.)
The reactant that will be in excess is X, and it will have 4 - 2.667 = 1.333 moles of X remaining.
Your final correct answer is 1.3 mol X left over.
