Anonymous
Anonymous asked in Science & MathematicsChemistry · 2 months ago

chemisty enthalpy?

Most integrated circuits are made from silicon, which can be obtained from an inexpensive starting material, SiO2 (sand). One step in the purification of silicon is to separate it from solid impurities by forming silicon tetrachloride gas. What is the overall enthalpy change when you convert 1.50 mol of silicon dioxide into pure silicon in the following three step process?

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SiO2(s)+2C(s)=Si(impure s)+2CO(g), delta H=+690 kJ

Si(impure s)+2Cl2(g)=SiCl4(g), delta H=-657 kJ

SiCl4(g)+2Mg(s)=2MgCl2(s)+Si(s), delta H=-625 kJ

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  • 2 months ago

    Add up all three equations:

    SiO2(s) + 2 C(s) + Si(impure s) + 2 Cl2(g) + SiCl4(g) + 2 Mg(s) →

    Si(impure s) + 2 CO(g) + SiCl4(g) + 2 MgCl2(s) + Si(s), ΔH = 690 kJ -657 kJ -625 kJ

    Cancel like amounts on opposite sides of the arrow, and do the arithmetic for ΔH :

    SiO2(s) + 2 C(s) + 2 Cl2(g) + 2 Mg(s) → 2 CO(g) + 2 MgCl2(s) + Si(s), ΔH = -592 kJ

    (1.50 mol SiO2) x (-592 kJ / 1 mol SiO2) = -888 kJ

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