A branch of science that deals with the relation between chemical reaction and heat energy absorbed or released is called Thermo chemistry.
All those chemical reaction in which the heat energy absorbed is greater than the heat energy released during the process are called “ENDOTHERMIC REACTION. e.g.
H2 +I2 —> 2HI
CaCO3 –> CaO + CO2
CH3COOH + NaOH —-> CH3COONa + H20
All those chemical reaction in which heat energy released is greater than heat energy absorbed during the process are called EXOTHERMIC REACTIONS” e.g.
CH4 + O2 —> CO2 + H20 + Heat
CaCO3 + H20 —> Ca(OH)2 + CO2 + Heat
Fe + S —–>FeS+ Heat