Rate Laws

Introduction:

Thermodynamics versus Kinetics

Thermodynamics is all about the “if” of a reaction, such as whether the process can occur.  Kinetics is all about “how”, such as whether the reaction occurs fast or slow.  The kinetics of the process is how to overcome the energy barrier from the reactants to the products, while the thermodynamics ensures that the reaction is a favorable transformation.
For a process to occur, it must overcome the energy maximum, usually denoted Ea (activation energy).  The larger the barrier (Ea), which is the difference between the energy maximum and initial minimum, the more difficult the process to occur, which thus results in a slower rate.  For a reaction to occur, not only must the thermodynamically favored with a -ΔG (which could be referred to as the driving force), it must also be fast enough, which results from a small Ea.  
If a reaction is thermodynamically favored, that means that the products are in the lowest possible energy state.  If a reaction is kinetically favored, that means that the reaction went through the easiest possible direction, that is, it went in the direction with the lowest activation energy.  The diagram below describes a possible reaction that is helpful in the understanding of thermodynamics versus kinetics.