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, 156.7 kg of SiO2 is allowed to react with 78.2 kg of carbon to produce 66.2 kg of silicon.

Once the reaction has occurred as completely as possible, what mass (in g) of the excess reactant is left?

Answer 1

156.7 kg of SiO2 is allowed to react with 78.2 kg of carbon to produce 66.2 kg of silicon.

The reaction between SIO2 and C is represented as

SiO2 + 2C-----> Si + 2CO

1mole of SiO2 reacts with 2moles of C i.e., 60g of Sio2 reacts with 24 g of C

no.of moles of SiO2 added = 156.7 kg= 156700g/60g/mol = 2611.66 moles of SiO2

no. of moles of C added = 78.2 kg = 78200/12 = 6516.66

Since 1mole of SiO2 requires 2moles of C 2611.66moles requires 2611.66*2 = 5223.31 moles of C

The no. of excess of C moles left after complete reaction is 6516.66-5233.31 = 1283.35 moles

The mass of C left = 1283.35*12 = 15400.2 g