$Si(s)+O_2(g)Si{O}_2(s)at500C$

$(30)$ For Equilibrium between $Si$ and $Si{O}_2,$

a$)$ Determine the standard enthalpy, entropy and Gibbs free energy of formation of $Si{O}_2$ at $298K$ from Ellingham diagram. Compare the results in $1.a\mathrm{.}1$kcal$=4187$ joules. $T=O$ at $OK(-273C).$ Do not forget.

b$)$ Read the equilibrium oxygen pressure $p{O}_2(g),p{H}_2\frac{g}{p}{H}_{2}O(g)$ ratio, and pCO$\frac{g}{p}C{O}_2(g)$ ratio from the Ellingham diagram using correct scales at $500C!$

c$)$ Write chemical reactions used for these three different scales.

d$)$ What must be the gas mixture ratio, and pCO$\frac{g}{p}CO2(g)$ ratio$)$ for all to prevent $Si(s)$ from oxidation or to decompose $Si{O}_2?$ Use equilibrium constants!!