THERMOCHEMISTRY

Thermochemistry is a branch of physical chemistry which deals with the energy changes accompanying chemical transformations. This is also known as chemical energetics and is based on the first law of thermodynamics.


Chemical reactions are accompanied by the evolution or absorption of heat.

Endothermic Reactions.

In these chemical reactions, heat is absorbed by the reactants. It is possible when the bond energy of reactants is greater than that of the products.
At constant pressure, Hp >HR
At constant volume, Ep>ER

Chemical equation can be written as;
C(s) + H2O(g) = CO(g) + H2O(g) ; Enthalpy change= +31.4 kcal


Exothermic Reactions.

In these chemical reactions heat is evolved as a product of the reaction. It occurs when the bond energy of the reactants is less than that of the products.
At constant pressure, Hp < HR
At constant volume, Ep< ER

Chemical equation can be written as;
NaOH(aq) +HCl (aq) = NaCl(aq) +H 2O(l); Enthalpy change = -13.7 kcal