Question

Identify the limiting and excess reagent for each of the following scenarios involving the formation of silicone dioxide, SiO2.
If you could just get geared in the right direction that would be wonderful. I am just a bit confused with this question. Thank you.

a. 2 atoms of silicone and 2 molecules of oxygen gas
b. 28.1 g of silicone and 48.0 g of oxygen gas
c. 6 mol of silicone and 2 mol of oxygen gas

Answer 1

First I want to correct a common error among many. Silicon is the element in chemistry. Silicone is, for want of a better word, a plastic. Silicones are wonderful stuffs. You can read more about them here.
http://en.wikipedia.org/wiki/Silicone

Now for your question.
The equation is
Si + O2 ==> SiO2
Look at the coefficients. The equation tells you that 1 mol Si will react with 1 mol oxygen to form 1 mol SiO2. To cut it down to size, if we have 2 atoms of Si, we will need 1 molecules of O2 to react with 1 atom Si and another molecule of O2 to react with the other Si so if have 2 molecules of O2, everything comes out even and neither Si nor O2 is in excess.

b. Put this in moles.
28.1g/atomic mass Si = 1 mol
48.0g O2/32 = 1.50 moles.
Since they react 1 mol to 1 mol, Si is the limiting reagent and we have some O2 remain unreacted when all is done.
c. I will leave this for you.