The integrated circuits in your cell phone and computer are made from the semico

Question

The integrated circuits in your cell phone and computer are made from the semiconductor silicon. The silicon is obtained from a really inexpensive starting material, sand, which is primarily Sio2. One step in the purification of silicon is to separate it from solid impurities by forming the gas silicon tetrachloride. Given the following reactions, what is the overall enthalpy of change in converting 1.00 mol of silicon dioxide into pure silicon. AH (kJ/mol) Steps in the purification SiO2(s) + 2 C(s) Si(impure s) + 2 CO(g) Si(impure s) + 2 C12(g) SiCl4(g) SiCl4(g) + 2 Mg(s) 2 MgC12(s) + Si(s) +690 -657 -625

Explanation / Answer

SiO2(s)+ 2C(s)-----> Si( impure s)+ 2CO, deltaH=+690 Kj/mole (1)

Si( impure S)+ 2Cl2(g) ------>SiCl4 (g)    deltaH=-657 Kj/mole (2)

addition of Eq.1 and 2 gives SiO2(s)+ 2C(s)+2Cl2(g) ------->SiCl4(g)+2Co(g), deltaH= 690-657= 33 Kj/mole (4)

Eq.33 is SiCl4(g)+2Mg(s)-------->2MgCl2+Si(s), deltaH =-625 Kj/mole (3)

addition of Eq.4 and Eq.3 gives SiO2(s)+2C(s)+2Cl2(g) ------->SiCl4(g)+2CO(g)+2MgCl2+Si(s), delta H= 33-625= -592 Kj/mole

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