CaCO3(s) ⇆ CaO(s) + CO2(g) A 2.00 mol sample of CaCO3(s) is placed in a rigid 100. L reaction vessel from which all the air has been evacuated. The vessel is heated to 898°C at which time the pressure of CO2(g) in the vessel is constant at 1.00 atm , while some CaCO3(s) remains in the vessel. Write the expression for Kp , the equilibrium constant for the reaction, and determine its value at 898°C .