Thermodynamics and chemical kinetics
Let us consider the formation of water (H2O):
2H2(g) + O2 (g) 2H2O (l)   ΔG = −221 KJ/mole
When we mix H2 gas and O2 gas in a container at room temperature and at atmospheric pressure we observe only a little bit of water or no water is formed.
Consider the decomposition of N2O4:
Since ΔG is +ve for the above reaction, according to thermodynamics it is non spontaneous but it occurs
rapidly. By observing the above two reactions, formation of water is spontaneous but it won't occur
rapidly where as decomposition of N2O4 is non‐spontaneous but it occurs rapidly.
In summary we can say that thermodynamics can predict the feasibility(either spontaneous or non‐spontaneous) of the reaction but, it can't predict the rate of reaction.
This is the major drawback of thermodynamics.
But chemical kinetics overcomes this drawback.
So, chemical kinetics is a complementary treat of thermodynamics, which deals with the
rate of reaction and conditions that affect the rate of reaction.