What Is the Eyring Equation?

eyring-equation Credit: iStock

The Eyring Equation, also called the Eyring-Polanyi Equation, is used to calculate the rate of a chemical reaction at different temperatures in the field of chemical kinetics. It is written as k = (k_b[t])/h) * e^(-delta.G/Rt). The Eyring Equation was developed in 1935 by theoretical chemist Henry Eyring.

Chemical kinetics is the study of chemical reactions, with particular attention to the speed at which they happen. Scientists who study chemical kinetics are interested in determining how quickly specific chemical reactions happen, what affects the speed at which these reactions happen, and what additional variables affect the nature of chemical reactions.

Some variables that have the potential to affect the speed of a chemical reaction are temperature, the composition of the chemicals involved, and the presence of catalysts, or substances that speed up and facilitate chemical reactions.

In the Eyring equation, "k" equals the reaction rate constant, "t" equals the temperature, "k_b" equals the Boltzmann constant, "h" equals Planck's constant, "delta G" is the Gibbs energy of activation and "R" is the gas constant. The formula can also be rewritten in terms of either the enthalpy of activation or the entropy of activation. Without a specific value for "k," the equation can also be used to find the ratios of the constants in regards to different temperatures for a reaction.

The Eyring equation is similar to the Arrhenius Equation, which is also used to determine how the rate of a chemical reaction changes based on temperature. However, while the Arrhenius Equation is limited by its inability to be applied to any reactions outside of gas-phase kinetics, the Eyring Equation can be used to study gas, condensed, and mixed-phase reactions.