chemical Reactions

Thermodynamics And kinetics of chemical Reactions

The kinetics and the thermodynamic properties are interrelated. One can explain the relation between them with the help of a chemical reaction. It is important to note that both thermodynamic and kinetic factors are related to chemical reactions. The quantity associated with kinetics is the rate constant (k) and this constant is correlated with the activation energy required to start the process, that is to say, the reactivity of the reactants.

The Chemical kinetics describes the rate of the reaction and how fast the equilibrium is reached. Until the reaction is stabilized, it does not provide any information about the reaction conditions. Reactivity of the reaction is related to the Chemical kinetics. Although thermodynamics only includes information about the product’s equilibrium state after the reaction has been completed, it fails to explain the rate of reaction. So the stability of the products is related to thermodynamics.

Kinetics Perspective

Kinetics Perspective
  • Kinetics evaluates the reaction rates and how it affects the reaction. Many variables can impact a reaction rate, including pressure, concentration, temperature and enzyme activity. 
  • For example, a molecule’s kinetic energy is directly related to its temperature, so that the increase in temperature leads to the rise in the reaction rate.
  • Before the reaction can proceed, it must have some input energy; otherwise, the reactants can not reach the threshold energy for activation and transform into products. 
  • The reaction is caused by various energy sources delivering energy to the reactants. 
  • The reaction rate, the rate constant and the kinetic energy need for reaction activation signifies how quickly the reaction reaches equilibrium.

Thermodynamic Perspective

Thermodynamic Perspective

Thermodynamics is considered as a form of energy which is stored in a reaction, a product, or a reactant. Thermodynamics is assumed to be the different form of energy that is transformed when a reaction is initiated or released. 

The concept of thermodynamics as per the Gibbs free energy (ΔG) is

  1. Spontaneous Reaction – During spontaneous reaction or exergonic reaction, the ΔG value is negative (-ve), which indicates the during the chemical reaction energy is released.
  2. Non-spontaneous reaction – During the non-spontaneous reaction or endergonic reaction, the ΔG value is positive (+ve), which indicates that during the chemical reaction energy is absorbed.

The thermodynamic reaction prefers the products and results in a spontaneous reaction occurring without the assistance of a continuous source of energy. It implies the product is the most stable phase of the chemical reactions. Thermodynamics describes the free energy between the products and the reactants. Because thermodynamic values can only be applied after reactants are converted to products and that reflect the equilibrium state. The below equation represents the relation between various thermodynamic quantities and free energy.

G = U + PV – TS


U = System’s Internal energy 

P = Pressure

V = Volume

T = Temperature 

S = Entropy of the system.

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