Question

$\Delta G_f^o$ (standard free energy of formation) of $ZnO$ and $CO$ are -318.2 kJ mol${}^{-1}$ and -137.3 kJ mol${}^{-1}$ respectively.

$ZnO+C⟶Zn+CO$

The approximate value of $\Delta G_f^o$ in kJmol${}^{-1}$ for the above reaction is _______kJ mol${}^{-1}$.

[Write your answer in form of inearest integer]

Answer 1

$Zn+\frac{1}{2}{O}_2\to ZnO$ , $\Delta G_f^o$ = - 318.2 kJ/mol

$C+\frac{1}{2}{O}_2\to CO$ , $\Delta G_f^o$ = -137.3 kJ/mol

$ZnO+C⟶Zn+CO$

$\Delta G^o=\Delta G_f^o\left(CO\right)-\Delta G_f^o\left(ZnO\right)$

$=-137.3-(-318.2)$

$=180.9\approx 181$ kJ mol${}^{-1}$

Positive value of $\Delta G^o$ indictes that reaction is non-spontaneous.

(However, it is spontaneous above 1000${}^o$C).