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Homework Help: Limiting Reagent Calculation

  1. Aug 17, 2014 #1
    1. The problem statement, all variables and given/known data

    Under appropriate conditions, the reaction of elemental phosphorus and elemental sulfur produces the compound P4S10. How much P4S10 can be prepared starting with 10.0 g of P4 and 30.0 g of S8?
    Answer 35.9g

    2. Step Sources
    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.

    3. My attempt 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!!!
  2. jcsd
  3. Aug 18, 2014 #2


    User Avatar

    Staff: Mentor

    Count atoms of any element of the LHS (left hand side) and on the RHS of the reaction equation. Are they equal?
  4. Aug 18, 2014 #3
    I'm trying to teach myself chemistry and balancing equations is still a weakness.
    I got it now thank you
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