Eyring equation
The Eyring equation (occasionally also known as Eyring–Polanyi equation) is an equation used in chemical kinetics to describe the variance of the rate of a chemical reaction with temperature. It was developed almost simultaneously in 1935 by Henry Eyring, Meredith Gwynne Evans and Michael Polanyi. This equation follows from the transition state theory (aka, activated-complex theory) and is trivially equivalent to the empirical Arrhenius equation which are both readily derived from statistical thermodynamics in the kinetic theory of gases.
General form
The general form of the Eyring–Polanyi equation somewhat resembles the Arrhenius equation:
where ΔG‡ is the Gibbs energy of activation, kB is Boltzmann's constant, and h is Planck's constant.
It can be rewritten as:
To find the linear form of the Eyring-Polanyi equation:
where:
= reaction rate constant
= absolute temperature
= enthalpy of activation
= gas constant
= Boltzmann constant
= Planck's constant
= entropy of activation
A certain chemical reaction is performed at different temperatures and the reaction rate is determined. The plot of 
versus 
gives a straight line with slope 
from which the enthalpy of activation can be derived and with intercept 
from which the entropy of activation is derived.
Temperature dependence of liquid viscosity
The temperature dependence of liquid viscosity is the phenomenon by which liquid viscosity tends to decrease (or, alternatively, its fluidity tends to increase) as its temperature increases. This can be observed, for example, by watching how cooking oil appears to move more fluidly upon a frying pan after being heated by a stove.
Physical causes
A molecular view of liquids can be used for a qualitative picture of the process of decrease in the shear (or bulk) viscosity of a simple fluid with temperature. As the temperature increases, the time of interaction between neighbouring molecules of a liquid decreases because of the increased velocities of individual molecules. The macroscopic effect is that the intermolecular force appears to decrease and so does the bulk (or shear) viscosity. The actual process can be quite complex and is typically represented by simplified mathematical or empirical models, some of which are discussed below. The models are valid over limited temperature ranges and for selected materials.
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