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)
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.
so i got that it was a 2 to 1 ratio what do i do after that?
hydrogen is 2 phosphrous is 1
What 2 to 1 ratio? The reaction is:
The limiting reagent is the reactant that you don't have enough of. Read my response to your question more carefully.
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 can't put it better than GK did. GK gave you step by step instructions.
Its 6.8 grams. the people above me don't know what they're talking about.