March 26, 2017

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Tetraphosphorus trisulphide (P4S3) is used in the match heads of some matches. It is produced in the reaction 8P4+3S8 --> 8P4S3. Determine which of the following statements are incorrect, and rewrite the incorrect statements to make them correct.

a. 4 mol P4 reacts with 1.5 mol S8 to form 4 mol P4S3
b. sulfur is the limiting reactant when 4 mol P4 and 4 mol S8 react.
c. 6 mol P4 reacts with 6 mol S8 forming 1320 g P4S3.

I don't get how to do this! If I just get an idea of how to set it up then I can figure it out! And for the first one I think it is incorrect, but I'm not sure...? Thanks!!

  • chemistry - ,

    a is correct.
    4 moles P4/8 moles P4 = 1/2 as much.
    1.5 is 1/2 of 3 for S
    4 is 1/2 8 for P4S3.
    All of the ratios stayed the same; therefore, you've simply cut the reaction in 1/2.

    b. Do this twice to make sure you are right. Use the coefficients in the balanced equation.
    (1) compare P to S
    (2) compare S to P.
    (1)4 mol P4 should take 1.5 mol S8. Do you have 1.5 mols S8? yes, you have 4 moles; therefore, you have more than enough S8 to react so P MUST THE THE LIMITING REAGENT.
    (2) We think we know the answer but we do this to make sure we are right.
    4 mol S8 *(8 moles P4/3 moles S8) = 10.7 moles P4 needed to react with 4 mol S8. Do we have 10.7 moles P4? No, we have only 4; therefore, P must be the limiting reagent.
    c. This is a limiting reagent problem. Determine which is the limiting reagent, use that and the coefficients to convert the amount of the limiting reagent to moles of the product, then convert mols product to grams of product and see if that equals 1320 g.

  • chemistry - ,


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