Question

In conversion of lime-stone to lime, CaCO3 (s) $\rightarrow$CaO(s) + CO2 (g) the values of $\Delta$H0 and$\Delta$S0 are + 179.1 kJ mol–1 and 160.2 J/K respectively at 298 K and 1 bar. Assuming that $\Delta$H⁰ and $\Delta$S⁰ do not change with temperature, temperature above which conversion of limestone to lime will be spontaneous is :

• A. 845 K
• B. 1118 K
• C. 1008
• D. 1200 K

Answer 1

Answer: (B)

1118 K

Answer 2

$\Delta$G⁰ = $\Delta$H⁰ – T$\Delta$S⁰

for a spontaneous process $\Delta$G⁰ < 0

$\Rightarrow \Delta$H⁰ – T$\Delta$S⁰ < 0 $\Rightarrow$ T$\Delta$S⁰ > $\Delta$H⁰ $\Rightarrow$ T > $\frac{\Delta H^{0}}{\Delta S^{0}}$ $\Rightarrow$ T > $\frac{179.1 \times 1000}{160.2} \Rightarrow$ T > 1117.9 K $\approx$ 1118 K.