HEAT OF REACTION
For a chemical reaction, reactants are combined or decomposed to form products, energy of the whole system changes.
The change of energy is mostly observed in the form of heat. Heat of reaction is symbolised as DH
Exothermic reaction : heat releases from the system. Products are more stable than reactants such as in bonding process. DH is negative.
Endothermic reaction : heat is absorbed into the system. Products are less stable than reactants such as breaking bond process. DH is positive.