During chemical reactions the bonds between atoms break and new bonds form. Energy must be absorbed to break a bond, so breaking bonds is endothermic. Making new bonds is exothermic because energy is released. When green copper carbonate decomposes, the equation is:

The equation is: CuCO3 (s) → CuO (s) + CO2 (g)

Explanation:

Copper carbonate decomposes at high temperatures, generating the products carbon dioxide (CO2) and copper oxide (II) CuO. In this type of decomposition reaction, a substance is broken generating two different compounds.