[Levathian]

Question: 
The reaction of phosphorus and sulfur produces P₄S₁₀. How much P₄S₁₀ is created from 10.0 g of P₄ and 30.0 g of S₈?
Answer: 35.9 g

My work thus far:
Balanced Equation: 4P₄ + 5S₈ -> 5(P₄S₁₀)
(perhaps this is the source of my inaccuracy)

1. moles: P₄ = .081
           s₈ = .1169
Limiting Reagent is P₄

2. comparing coefficients (stoichiometric moles): .081 molP₄ x (5molP₄S₁₀ / 4 mol p₄) = (.081 x 5)/4 = .100875 mol of P₄S₁₀
4. .100875 x molar mass of p4s10 = 44.83 grams.

This is however incorrect.
I get the correct answer when multiplying strait out the moles of p₄ (.0807) by the molar mass of P₄S₁₀. Is my balanced equation wrong?

Any help is appreciated!!!


I'm following the steps from
"General Chemistry: principles and patterns v1" by Bruce Averill and Patricia Eldredge
 Chapter 3.4
1. Determine the number of moles of each reactant.
2. Compare the mole ratio of the reactants with the ratio in the balanced chemical equation to determine which reactant is limiting.
3. Calculate the number of moles of product that can be obtained from the limiting reactant.
4. Convert the number of moles of product to mass of product.

[Borek]

(perhaps this is the source of my inaccuracy)

Indeed.

[Vidya]

in the balanced equation you should have 40 S on both the sides.So P4S10 should be multiplied by 4 so that P and S will be equal to number on the left side.

[Babcock_Hall]

There are two separate issues here.  One is do you have the correct balanced equation?  Two is that (assuming the correct balanced equation is in place), is your methodology for calculating the limiting reagent  sound?  I will only address the second issue, because I suspect you are going off on the wrong track.  It seems to me (based on point 1 in your post) that you are comparing the number of moles of phosphorus to the number of moles of sulfur and concluding that phosphorus is limiting on that basis alone.  Suppose that your recipe for making a cheese sandwich is 2 slices of bread plus one slice of cheese equals one cheese sandwich.  Now suppose that you have six slices of bread and four slices of cheese.  Is the cheese the limiting reagent?  If not, then how can we fix our algebra to take this into consideration?