Homework Help: chemistry

Posted by Miley on Tuesday, June 10, 2008 at 8:36pm.

What is the maximum number of grams of PH3 that can be formed when 6.2 grams of phosphorus reacts with 4.0 grams of hydrogen to form PH3?
P4+6H2-->4PH3.

how do i do this question

chemistry - GK, Tuesday, June 10, 2008 at 9:12pm
Convert grams of phosphorus to moles of P4. Do likewise for grams of hydrogen, H2. To convert grams to moles you divide grams by the formula mass of that substance. The mole ratio of H2 reacting with P4 is 6/1.
If the number of moles of H2 is 6 times (or greater) the moles of P4, phosphorus is the limiting reagent.
If (moles of H2)/(moles P4) is less than 6, H2 is the limiting reagent.
Depending on which reagent is limiting,
moles of PH3=(mol H2)(4 mol PH3 / 6 mol H2)
or
moles of PH3=(mol P4)(4 mol PH3 / 1 mol P4)
After finding the moles of PH3, you convert them to grams by multiplying by the formula mass of PH3.
- chemistry - Miley, Tuesday, June 10, 2008 at 9:18pm
  so i got that it was a 2 to 1 ratio what do i do after that?
  hydrogen is 2 phosphrous is 1
  - chemistry - GK, Tuesday, June 10, 2008 at 9:52pm
    What 2 to 1 ratio? The reaction is:
    P4+6H2-->4PH3.
    The limiting reagent is the reactant that you don't have enough of. Read my response to your question more carefully.
  - chemistry - Miley, Tuesday, June 10, 2008 at 10:01pm
    here is my work:
    i got 27.2 grams phosphorous and 45.3 grams hydrogen.
    
    i divided the phosphorous by the hydrogen and got a 2 to one ratio. what do i do after that?
    
    I'M CONFUSEDDDDDDDDD
chemistry - DrBob222, Wednesday, June 11, 2008 at 12:05am
I can't put it better than GK did. GK gave you step by step instructions.
chemistry - Raded, Thursday, January 1, 2009 at 12:41pm
45 g
chemistry - Joe, Friday, January 8, 2010 at 3:45pm
45g
chemistry - seano, Thursday, June 10, 2010 at 1:02am
45.2
chemistry - Anonymous, Wednesday, May 30, 2012 at 10:55am
Jdjdj
chemistry - Daniel, Wednesday, November 14, 2012 at 7:25pm
Its 6.8 grams. the people above me dont know what theyre talking about.

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