Question

Many computer chips are manufactured from silicon, which occurs in nature as SiO2. When SiO2 is heated to melting, it reacts with solid carbon to form liquid silicon and carbon monoxide gas. In an industrial preparation of silicon, 156.4 kg of SiO2 is allowed to react with 79.0 kg of carbon to produce 66.2 kg of silicon

A) Determine the theoretical yield for the reaction. Express your answer using four significant figures

B)Determine the percent yield for the reaction.

Answer 1

SiO2(s) + 2C(s) ----------------- Si (l) +2 CO(g)

mass of SiO2= 156.4 Kg

molar mass of SiO2= 60.1 g/mole = 0.0601 Kg

number of moles of SiO2 = mass/molar mass= 156.4/0.0601 =2602.33 moles

mass of Carbon= 79.0kg

molar mass of Carbon= 12.0g/mole = 0.012 kg

number of moles of carbon = 79.0/0.0120 =6583.33 moles

according to equation

1 mole of SiO2 = 2 moles of C

2602.33 moles of SIO2 = ?

                                       = 2x2602.33/1= 5204.66 moles of C

we need 5204.66 moles of Carbon. but we have 6583.33 moles of Carbon. SO Carbon in excess reagent.

Hence SiO2 is limiting reagent.

according to equation

1 mole of SiO2 = 1 mole of Si

2602.33 moles of SiO2= 2602.33 moles of Si

number of moles of Si formed = 2602.33 moles

molar mass of Si = 28.08 gra,/mole

mass of 2602.33 moles of Si = 2602.33x28.08 = 73073.43 grams = 73.07 Kg

Theoritical yield of Si = 73.07 Kg

Actual yield = 66.2 kg

Percent yield = Actual yield/Theoritical yield x10

Percent yield = 66.2/73.07 x100 = 90.598 %

Percent yield = 90.6%.