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.
a) When green copper carbonate decomposes, the equation is:
CuCO3 CuO CO2
copper carbonate copper oxide carbon dioxide
Is the reaction exothermic or endothermic? Use ideas about bonds to explain why.