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Limiting Reactants

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Hemidol:
Elemental phosphorus is produced by the reaction,
2 Ca3(PO4)2 + 6 SiO2 + 10 C ® 6 CaSiO3 + 10 CO + P4
Suppose that you have 10.5 moles of Ca3(PO4)2, 34.5 moles of SiO2, and 67.5 moles of C.

(a) Which reactant is limiting?
(b) What are the maximum amounts (in moles) of CaSiO3, CO, and P4 that can be produced from
these amounts of reactants?


How can I go about solving this question?

Ak:
so for the first one u just do some mole conversions and see if u react 10.5 moles of Ca3(PO4)2 how many moles of the other 2 are needed and do the same thing with the other 2 reactants and determine which one is limiting.

Ex. (10.5 moles Ca3(PO4)2  * 6 moles of SiO2) / 2 moles Ca3(PO4)2 = 31.5 moles SiO2 are needed

so does that mean that Ca3(PO4)2 is limiting or not? and try it out for the other ones too.

for the second you take the limiting reagent and do mole conversions to get the max number of moles for the products

Hemidol:
Hi there,

I'm sorry but I'm still confused after your reply. I was orginally doing this technique:

10.5 mole Ca3(PO4)2 * (6 mole CaSiO3 / 2 mole Ca3(PO4)2 ) = 31.5 mole

34.5 mole SiO2 * (6 mole CaSiO3 / 6 mole SiO2) = 34.5 mole

67.5 mole C * (6 mole CaSiO3 / 10 mole C) = 40.5 mole

And thus the Ca3(PO4)2 compound is the limiting reagent. However your doing a completely different technique. Would you mind explaining your technique a bit more and if the method I just did is incorrect?

Ak:
you got the right answer but well the way i was taught was that u convert Ca3(PO4)2 to moles of SiO2 and also moles of C

you end up with:

10.5 mole Ca3(PO4)2 * (6 mole SiO3 / 2 mole Ca3(PO4)2 ) = 31.5 mole
10.5 mole Ca3(PO4)2 * (10 mole C / 2 mole Ca3(PO4)2 ) = 52.5 mole

this means that if u wanna react 10.5 moles of Ca3(PO4)2 you need at least 31.5 mole of SiO3 and 52.5 moles of C and as you can see you have enough.  This doesn't really tell you anything, so u go on to the next one.

34.5 mole SiO3 * (2 mole  Ca3(PO4)2 / 6 mole SiO3 ) = 11.5 mole
34.5 mole SiO3* (10 mole C / 6 mole SiO3) = 57.5 mole

so to react 34.5 moles of SiO3 you need at least 11.5 moles of Ca3(PO4)2 and 57.5 moles of C.  You have enough C but you dont have enough Ca3(PO4)2, meaning that it is the limiting reactant.

See its limiting because, your gonna run out of that before you run out of any other reactants so in the end, you'll still have some SioO3 and C left over

Hemidol:
I see, thanks a lot. What are the maximum amounts (in moles) of CaSiO3, CO, and P4 that can be produced from
these amounts of reactants?


P.s. the orginial post (just so you know) should read:
2 Ca3(PO4)2 + 6 SiO2 + 10 C -> 6 CaSiO3 + 10 CO + P4

Ignore the "®" symbol, it should be a "->"

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