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while for bimolecular gas reactions A = (e 2 k B T/h) (RT/p) exp(ΔS ‡ /R). In these equations e is the base of natural logarithms, h is the Planck constant, k B is the Boltzmann constant and T the absolute temperature. R′ is the ideal gas constant. The factor is needed because of the pressure dependence of the reaction rate.
To calculate the maximum possible value for a non-tunneling 2 H KIE, we consider the case where the ZPE difference between the stretching vibrations of a C-1 H bond (3000 cm −1) and C-2 H bond (2200 cm −1) disappears in the transition state (an energy difference of [3000 – 2200 cm −1]/2 = 400 cm −1 ≈ 1.15 kcal/mol), without any ...
For a thermodynamically-controlled reaction, every difference of RT ln 10 ≈ (1.987 × 10 −3 kcal/mol K)(298 K)(2.303) ≈ 1.36 kcal/mol in the free energies of products A and B results in a factor of 10 in selectivity at room temperature (298 K), a principle known as the "1.36 rule":
A catalyst is able to reduce the activation energy by forming a transition state in a more favorable manner. Catalysts, by nature, create a more "comfortable" fit for the substrate of a reaction to progress to a transition state. This is possible due to a release of energy that occurs when the substrate binds to the active site of a catalyst ...
The general form of the Eyring–Polanyi equation somewhat resembles the Arrhenius equation: = ‡ where is the rate constant, ‡ is the Gibbs energy of activation, is the transmission coefficient, is the Boltzmann constant, is the temperature, and is the Planck constant.
If the reaction is first order it has the unit s −1, and for that reason it is often called the frequency factor or attempt frequency of the reaction. Most simply, k is the number of collisions that result in a reaction per second, A is the number of collisions (leading to a reaction or not) per second occurring with the proper orientation to ...
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".
These phenomena are due to exothermic or endothermic reactions occurring faster than heat transfer, causing the reacting molecules to have non-thermal energy distributions (non-Boltzmann distribution). Increasing the pressure increases the heat transfer rate between the reacting molecules and the rest of the system, reducing this effect.