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A plot illustrating the dependence on temperature of the rates of chemical reactions and various biological processes, for several different Q 10 temperature coefficients. The rate ratio at a temperature increase of 10 degrees (marked by points) is equal to the Q 10 coefficient.
Here α has the dimension of an inverse temperature and can be expressed e.g. in 1/K or K −1. If the temperature coefficient itself does not vary too much with temperature and , a linear approximation will be useful in estimating the value R of a property at a temperature T, given its value R 0 at a reference temperature T 0:
In physical chemistry, the Arrhenius equation is a formula for the temperature dependence of reaction rates.The equation was proposed by Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van 't Hoff who had noted in 1884 that the van 't Hoff equation for the temperature dependence of equilibrium constants suggests such a formula for the rates of both forward and ...
Understanding the temperature dependence of viscosity is important for many applications, for instance engineering lubricants that perform well under varying temperature conditions (such as in a car engine), since the performance of a lubricant depends in part on its viscosity.
The Van 't Hoff equation relates the change in the equilibrium constant, K eq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, Δ r H ⊖, for the process. The subscript r {\displaystyle r} means "reaction" and the superscript ⊖ {\displaystyle \ominus } means "standard".
Substituting for the quotient in the exponent of : / = where the approximate value for R is 8.31446 J K −1 mol −1 The activation energy of this reaction from these data is then: E a = R × 12,667 K = 105,300 J mol −1 = 105.3 kJ mol −1 .
The following is a table of some constant-pressure molar heat capacities c P,m of various diatomic gases at standard temperature (25 °C = 298 K), at 500 °C, and at 5000 °C, and the apparent number of degrees of freedom f * estimated by the formula f * = 2c P,m /R − 2:
This equation can be used to calculate the value of log K at a temperature, T 2, knowing the value at temperature T 1. The van 't Hoff equation also shows that, for an exothermic reaction (<), when temperature increases K decreases and when temperature decreases K increases, in accordance with Le Chatelier's principle.