Question

What is the minimum partial pressure of carbon dioxide required to change calcium oxide to calcium carbonate (calcite) at 25 degrees Celcius?

Answer 1

The reaction is CaO(s)+ CO2(g)<------->CaCO3(s)

Standard free energy change = sum of standard free energy change of products - sum of standard free energy change of reactants

standard free energy data (Kj/mole): CaCO3= -1127.8 , CaO= -603.54 and CO2=-394.5

Standard gibbs free energy change= 1*standard free energy of CaCO3- (1*standard free energy of CaO+ 1*standard free energy of CO2)= -1127.8-(-603.54-394.5)=-129.76 KJ/mole

where 1,1, and 1 are coefficients of CaCO3, CaO and CO2 respectively.

deltaG=-RT lnK, K= Equilibrium constant and R= 8.314 J/mole.K, T= 298K

lnK= -deltaG/RT= 129.76*1000/(8.314*298), K= 5.567*10²²

for the reaction given since the activity of solids CaO and CaCO3 are unity, K= 1/PCO2, PCO2= Pressrue of CO2

PCO2= 1/K= 1/(5.567*10²²) atm=1.8*10^-23 atm