Difference Between Thermodynamics and Kinetics

Thermodynamics vs Kinetics

Both thermodynamics and kinetics are scientific principles that draw their roots from the physical sciences and have brought about so many advancements in the scientific domain, with its applications running into many fields of science and engineering. The two terms literally go hand in hand in the chemical sciences and are very closely related.

More about Thermodynamics

The name ‘Thermodynamics’ itself suggests the meaning of the term which can be referred to as ‘thermo’ relating to temperature and ‘dynamics’ relating to change. Hence more loosely it can be thought as changes that occur due to temperature. These changes can be physical and/or chemical in nature. The changes that occur chemically are termed as ‘chemical reactions’, and this gave rise to chemical thermodynamics.

On a more general reference, thermodynamics can be described as a principle related to bodies/states and processes. Usually the processes involved are energy transfers, which can be divided into two distinct groups; i.e. heat and work. If one energy state changes to another, we say that work is done. Energy is basically the capacity to do work. If the energy of a system changes as a result of the difference in temperature, we say there has been a flow of heat.

Therefore, thermodynamics is mainly concerned with energetics and gives no explanation whatsoever about the rate of the occurrence of these changes. This distinction of the rates and energetics involved in states/bodies and processes is very clear in the domain of chemical sciences where thermodynamics is only concerned with the energetics and the position of equilibrium of a chemical reaction.

The position of equilibrium is where both the reactants and products are present and the concentrations of all species involved stays without changing over time, and it is specific for a particular reaction when the reaction is done under standard conditions. Thermodynamics may predict that a reaction will definitely take place because the energy of the products is less than that of the reactants. However, in practice, one may need the principle of kinetics to make the reaction happen at an appreciable rate.

More about Kinetics

Kinetics is more often involved in the field of chemical sciences. Hence it relates as to how fast a chemical reaction might occur or how fast the chemical equilibrium point is reached. Various parameters are associated with the control of the rates of chemical reactions.

The molecules involved must collide with sufficient energy and in the proper orientation. Any condition that meets this requirement increases the rate of a chemical reaction. There is an energy barrier for any chemical reaction to take place. This is known as the activation energy. The energy of the molecules should be greater than this energy for the reaction to take place. Increasing the temperature increases the rate of a reaction by supplying energy greater than the activation energy, to a higher fraction of molecules. Increasing the surface area allows more collisions and increasing the concentration increases the number of reacting molecules thereby increasing the rate of the reaction. Catalysts are used to lower the activation energy barrier and thereby provide an easy route for the reaction to occur.

Thermodynamics vs Kinetics

  • Thermodynamics is only concerned with the energetics and the position of equilibrium when going from one state to another; whereas kinetics relates to the rates of the processes between states.
  • In the chemical sciences, thermodynamics tells us how far a reaction takes place, but kinetics tells us how fast a reaction would take place.