Considering the Formation reaction for Silica (reaction 3)... Find the enthalpy

Question

Considering the Formation reaction for Silica (reaction 3)...

Find the enthalpy of formation for SiO2 at STP (in symbols and in numbers) reaction (3).

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Find the entropy of formation for SiO2 at STP (in symbols and in numbers) reaction (3).

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Find the free energy of formation for SiO2 at STP (in symbols and in numbers) reaction (3).

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Find the equilibrium constant for reaction (3) at STP (in symbols and in numbers).

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Find the enthalpy of formation for SiO2 at 500 K,1 atm (in symbols and in numbers) reaction (3).

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On reverse side, find the equilibrium constant for reaction (3) at 500K (in symbols & in numbers).

Explanation / Answer

Considering the Formation reaction for Silica

Si (s) + O2 (g) -----------------> SiO2 (s)

enthalpy of formation for SiO2 at STP

Hforxn = Hoproducts - Horeactants

            = HoSiO2 - (HoSi + HoO2)

= - 910.94 - (0 + 0)

= - 910.94 kJ/mol

Hfo = - 910.94 kJ/mol

entropy of formation for SiO2 at STP

Sforxn = SoSiO2 - (SoSi + SoO2)

= 41.84 - (18.83 + 205.03)

   = -182.02 J/K

Sfo = - 182.02 J/K

free energy of formation for SiO2 at STP

Gof = Hf - T x Sf

= - 910.94 - 298 x -182.02 x 10^-3

= - 856.67 kJ/mol

Gof = - 856.67 kJ/mol

equilibrium constant for reaction (3) at STP

Go = - RT ln K

- 856.67 = - 8.314 x 10^-3 x 298 x ln K

K = 1.46 x 10^150

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