You are currently viewing Difference Between Arrhenius and Eyring Equation

Difference Between Arrhenius and Eyring Equation

  • Post last modified:April 3, 2023
  • Reading time:8 mins read
  • Post category:Chemistry
  • Post author:

Explanation of Arrhenius and Eyring Equation

The Arrhenius and Eyring Equations are both used to describe the rate of chemical reactions by taking into account the temperature dependence of reaction rates.

The Arrhenius equation was developed by Swedish scientist Svante Arrhenius in 1889. It describes the dependence of the reaction rate constant (k) on the temperature (T) and the activation energy (Ea) required to initiate the reaction:

k = A * exp(-Ea/RT)

where A is the pre-exponential factor, R is the gas constant, and exp is the exponential function.

The Arrhenius equation shows that the rate of a chemical reaction increases with increasing temperature because the activation energy is more easily overcome at higher temperatures. It also shows that the rate constant decreases exponentially with increasing activation energy.

The Eyring equation, developed by American physical chemist Henry Eyring in 1935, is an extension of the Arrhenius equation that includes the entropy of activation (ΔS‡) in addition to the activation energy and temperature:

k = (kBT/h) * exp(-ΔG‡/RT)

where kB is the Boltzmann constant, h is Planck’s constant, and ΔG‡ is the Gibbs free energy of activation.

The Eyring equation provides a more accurate description of the temperature dependence of reaction rates, particularly for reactions that involve changes in entropy. It also takes into account the fact that the rate of a chemical reaction is determined by the rate of formation of the transition state.

Both the Arrhenius and Eyring equations are used to describe the temperature dependence of reaction rates, with the Eyring equation providing a more comprehensive description that includes the entropy of activation.

The role of reaction rates in chemical reactions

Reaction rates play a critical role in chemical reactions as they determine how quickly reactants are converted to products. The rate of a chemical reaction is defined as the change in concentration of a reactant or product over time. A faster reaction rate means that reactants are being converted to products more quickly, while a slower reaction rate means that the reaction is proceeding more slowly.

Reaction rates are important because they determine the efficiency of chemical reactions. For example, in many industrial processes, the reaction rate is a key factor in determining the overall productivity and profitability of the process. In biological systems, reaction rates are also critical as they determine the speed and efficiency of metabolic processes.

The rate of a chemical reaction is determined by a number of factors, including the concentration of reactants, the temperature, the presence of catalysts, and the surface area of reactants. By understanding the factors that affect the rate of a chemical reaction, scientists can optimize reaction conditions to maximize reaction efficiency and minimize unwanted side reactions.

The rate of a chemical reaction is a critical parameter that determines the speed and efficiency of the reaction. Understanding the factors that affect reaction rates is important for optimizing chemical reactions and improving reaction efficiency.

Arrhenius Equation

The Arrhenius equation is a mathematical formula that describes the temperature dependence of chemical reaction rates. It was developed by the Swedish chemist Svante Arrhenius in 1889 and is widely used in chemistry and chemical engineering to understand and optimize chemical reactions.

The Arrhenius equation relates the rate constant (k) of a chemical reaction to the temperature (T) and the activation energy (Ea) required for the reaction to occur:

k = A * exp(-Ea/RT)

where A is the pre-exponential factor, R is the gas constant, and exp is the exponential function.

The Arrhenius equation shows that the rate of a chemical reaction increases with increasing temperature, because the activation energy is more easily overcome at higher temperatures. It also shows that the rate constant decreases exponentially with increasing activation energy. The pre-exponential factor A is a constant that represents the frequency of collisions between reactant molecules, which is temperature-dependent.

The Arrhenius equation can be used to estimate how the rate of a chemical reaction will change with changes in temperature, which is useful for optimizing reaction conditions. For example, if a reaction is too slow, increasing the temperature can increase the reaction rate.

There is a limit to the increase in rate with temperature, as excessively high temperatures can lead to unwanted side reactions, decomposition, and loss of product yield.

The Arrhenius equation is an important tool for understanding and optimizing chemical reactions, and it provides a fundamental basis for the study of chemical kinetics.

Eyring Equation

The Eyring equation, also known as the Eyring–Polanyi equation, is a mathematical formula used to describe the temperature dependence of chemical reaction rates, particularly for reactions that involve changes in entropy. The equation was developed by the American physical chemist Henry Eyring in 1935, building upon the work of Michael Polanyi.

The Eyring equation relates the rate constant (k) of a chemical reaction to the temperature (T), the activation energy (Ea), and the entropy of activation (ΔS‡):

k = (kBT/h) * exp(-ΔG‡/RT)

where kB is the Boltzmann constant, h is Planck’s constant, ΔG‡ is the Gibbs free energy of activation, and exp is the exponential function.

The Eyring equation shows that the rate constant of a chemical reaction depends on the energy required to reach the activated complex and the entropy change associated with the transition from reactants to products. The equation takes into account the fact that the rate of a chemical reaction is determined by the rate of formation of the transition state.

The Eyring equation can be used to estimate how the rate of a chemical reaction will change with changes in temperature, and it provides a more comprehensive description of temperature dependence compared to the Arrhenius equation. The equation is particularly useful for reactions that involve changes in entropy, such as bimolecular reactions, where the entropy of activation plays a significant role.

The Eyring equation is an important tool for understanding and optimizing chemical reactions, particularly for reactions that involve changes in entropy. It provides a more accurate description of the temperature dependence of reaction rates compared to the Arrhenius equation, and it is widely used in chemical kinetics and chemical engineering.

Differences Between Arrhenius and Eyring Equation

The Arrhenius and Eyring equations are both mathematical formulas used to describe the temperature dependence of chemical reaction rates.

They have some key differences:

  1. Activation energy: The Arrhenius equation relates the rate constant to the activation energy, while the Eyring equation relates the rate constant to the Gibbs free energy of activation. The Gibbs free energy of activation takes into account the enthalpy and entropy changes associated with the transition state, while the activation energy only considers the enthalpy change.
  2. Entropy: The Arrhenius equation does not explicitly consider the entropy of activation, while the Eyring equation takes into account the entropy change associated with the transition state. This makes the Eyring equation more appropriate for reactions that involve changes in entropy.
  3. Pre-exponential factor: The Arrhenius equation includes a pre-exponential factor that accounts for the frequency of collisions between reactant molecules, which is temperature-dependent. The Eyring equation does not include this factor.
  4. Applicability: The Arrhenius equation is widely used in chemistry and chemical engineering to describe the temperature dependence of chemical reaction rates, while the Eyring equation is particularly useful for reactions that involve changes in entropy, such as bimolecular reactions.

The Arrhenius and Eyring equations are both important tools for understanding and optimizing chemical reactions, but they have some key differences in their mathematical formulations and applicability. The choice between the two equations depends on the specific reaction being studied and the factors that are most important for describing the reaction kinetics.

Conclusion

The Arrhenius and Eyring equations are both important mathematical formulas used to describe the temperature dependence of chemical reaction rates. While the Arrhenius equation is more commonly used and applicable to a wider range of reactions, the Eyring equation provides a more comprehensive description of temperature dependence, particularly for reactions that involve changes in entropy.

The choice of the equation depends on the specific reaction being studied and the factors that are most important for describing the reaction kinetics. Understanding the principles behind these equations is crucial for optimizing chemical reactions and designing efficient chemical processes.

Reference Website

Here are some websites that provide more information about the Arrhenius and Eyring equations:

  1. Khan Academy – Chemical kinetics: Arrhenius equation: https://www.khanacademy.org/science/chemistry/chemical-kinetics/arrhenius-equation/v/arrhenius-equation
  2. Chemical Engineering Guy – Eyring equation: https://www.chemicalengineeringguy.com/eyring-equation/
  3. Chemistry LibreTexts – Arrhenius equation: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/Rate_Laws/Arrhenius_Equation
  4. ScienceDirect – Eyring equation: https://www.sciencedirect.com/topics/chemistry/eyring-equation