Chemical Thermodynamics

In conversion of limestone to lime,

CaCO3(s) → CaO(s) + CO2(g)

The values of ΔH° and ΔS° are +179.1 kJ/mol and 160.2 J/K respectively at 298 K and 1 bar. Assuming that ΔH° and ΔS° do not change with temperature, temperature above which conversion of limestone to lime will be spontaneous is

  1. 1200 K
  2. 1118 K
  3. 1008 K
  4. 845 K

Answer

For ΔG° = ΔH° – TΔS°

For a spontaneous process ΔG° < 0

i.e. ΔH° – TΔS° < 0 or ΔH° < TΔS° or, TΔS° > ΔH°

T > ΔH°/ ΔS° i.e. 179.1 x 1000/160.2

or T > 1117.9 K = 1118 K

The correct option is B.