CaCO3 is a promising material for thermochemical energy storage (TCES) systems. It can store and release heat upon reversible decarbonation to CaO, which emits heat through carbonation. Decarbonation temperature of CaCO3 directly affects the properties of CaO, which influences heat supply in result. The current research studies CaCO3/CaO system, specifically analyzing the conversion of CaO into CaCO3 (carbonation) for various CaO samples prepared at decarbonation temperatures between 600 and 975 degrees C. A relation is developed using regression analysis to verify the linearity between reactivity of CaO samples and decarbonation temperature at which it was prepared. The carbonation of all CaO samples at various partial pressures of CO2 and temperatures is also analyzed. The whole process is performed for pure and SiO2 doped systems (molar ratio 1:1). The efficient performance of CaCO3/CaO system is noted for decarbonation temperatures above 750 degrees C or below 925 degrees C for pure material. While for doped material, the decarbonation temperature for efficient performance lies between 700 degrees C and 800 degrees C. Both systems performed with higher efficiency when CO2 pressure was kept constant and the carbonation temperature was increased.