The chemical reactions which take place with energy changes are known as thermochemistry. A thermochemistry deal with energy changes and it is a branch of chemistry. The energy changes occur mostly due to change of bond energy. Thermochemistry deals with two types of chemical reaction:
1. Exothermic Reactions
2. Endothermic Reactions
1. Exothermic Reactions: A chemical reaction which is accompanied by evolution of heat is known as exothermic reaction. In the exothermic reactions internal energy change has negative sign at constant temperature i.e. ∆U has negative sign.
2. Endothermic Reactions: A chemical reaction which is accompanied by absorption of heat is known as endothermic reaction. In the endothermic reactions internal energy change has positive sign at constant temperature i.e. ∆U has positive sign.
