Question

SiO2(s) + 3C(s) --> SiC(s) + 2CO(g)
How many liters of carbon monoxide (CO) are produced when you start with 13.4 grams of carbon (C) and an excess amount of SiO2?
How many liters of hydrogen gas (H2) can be produced when 12.5 grams of ZnCl2 is also produced at STP?
a.0.56 liters CO
b.2.78 liters CO
c.9.87 liters CO
d.16.7 liters CO

Answer 1

Since SiO2 is in excess the Carbon is the limiting reagent. In order to use stoichiometric ratios you must first convert to moles.

The molar mass of Carbon is 12 g/mol
13.4 g C * ( 1mol / 12 g) = 1.12 mol C

Now, for every 3 Carbon you get 2 Carbon monoxide.  
1.12 mol C * (2 CO / 3 C) = 0.74 mol CO

At Standard temperature and Pressure (STP); a mole of gas has a volume of 22.4 L. This is because everything in the Ideal Gas Law equation is held constant.

0.74 mol CO * ( 22.4 L/mol) = 16.7 L CO