In the presence of heat(Thermal decomposition reaction):
CaCO3(s)→CaO(s)+CO2(g)
In the presence of sunlight(Photolytic decomposition reaction):
2AgCl(s)→2Ag(s)+Cl2(g)
In the presence of electricity(Electrolytic decomposition reaction):
2H2O(l)→2H2(g)+O2(g)