Questions...thanks chemistry wizzes!...?
Questions 1 & 2 refer to this information:
The element silicon is becoming increasingly important in our technological society. It is used for computer chips and for ceramics such as the heat resistant coating on the space shuttle. The element is produced commercially by heating silica with carbon in an electric furnace at 2 000K, according to the equation
SiO2(l) + 2C(s) - (arrow) 2CO(g) + Si(l)
In a particular furnace, 300kg of SiO2 is heated with 180kg of carbon.
9. The excess reagent and amount left over is about
a) 120kg of SiO2
b) 60kg of SiO2
c) 120kg of carbon
d) 60kg of carbon
10. The mass of Si(l) produced is
a) 420 kg
b) 210 kg
c) 140kg
d) 280kg
Thanks. 1kg=1000g if that helps.
9. The amount of moles of SiO2:
moles = mass / molar mass
= 300 kg / 60.09 g/mol
= 5 kmol SiO2
moles of C = 180 kg / 12 g/mol
= 15 kmol
Since twice as many moles of C are required, we divide it by two.
= 7.5 eq of C vs 5 eq of SiO2
So the carbon is in excess. The amount excess would be 5 kmol (since 10 kmol are required to completely react with the 5 kmol of SiO2). 5 kmol of C would be 60 kg of carbon. So the answer is (d) for 9.
For 10. The mass of Si produced:
if 5 kmol of SiO2 are used (and it is the limiting reactant) than 5 kmol of Si will be produced.
mass = moles x molar mass
= 5 kmol Si x (28.09 g.mol Si)
= 140 kg
So the answer would be (c). 140 kg of silicon would be produced.
0-preparing activated carbon and ceramic rings for filter
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