John KellerGood luck!To estimate free energy of activation, you would need to optimize and do frequency calculation for the starting compound and transition state, and take the difference in free energies between these two. Locating the T.S. is sometimes difficult: if you are using Gaussian, the Opt=TS, or OPT=QST2, or Opt=QST3 methods are used.To a good approximation at moderate temperatures, the free energy of activation is not dependent on temperature. Reactions go faster at higher temperatures because a higher proportion of molecules have attained a kinetic energy greater or equal to the free energy of activation.Hi Ashutosh,You can use the Eyring-Polanyi equation to calculate k the unimolecular rate constant, given Gibbs Free Energy of Activation delGdoubledagger. Google "Eyring equation wiki" to see the equation written out.
On Thu, Apr 4, 2013 at 7:17 PM, ashutosh gupta ashu1809 a gmail.com <owner-chemistry]~[ccl.net> wrote:
Dear All,Normally it is assumed that if the activation barrier is less than 20 kcal/mol, then the reaction occurs at ROOM TEMPERATURE.how do we calculate it?what is its formula?how can we know corresponding energy in kcal/mol for some other temperature say 70 degree Celsius.thanking you.kind regards and best wishesashutoshvaranasi India
John KellerGood luck!To estimate free energy of activation, you would need to optimize and do frequency calculation for the starting compound and transition state, and take the difference in free energies between these two. Locating the T.S. is sometimes difficult: if you are using Gaussian, the Opt=TS, or OPT=QST2, or Opt=QST3 methods are used.To a good approximation at moderate temperatures, the free energy of activation is not dependent on temperature. Reactions go faster at higher temperatures because a higher proportion of molecules have attained a kinetic energy greater or equal to the free energy of activation.Hi Ashutosh,You can use the Eyring-Polanyi equation to calculate k the unimolecular rate constant, given Gibbs Free Energy of Activation delGdoubledagger. Google "Eyring equation wiki" to see the equation written out.
On Thu, Apr 4, 2013 at 7:17 PM, ashutosh gupta ashu1809 a gmail.com <owner-chemistry]~[ccl.net> wrote:
Dear All,Normally it is assumed that if the activation barrier is less than 20 kcal/mol, then the reaction occurs at ROOM TEMPERATURE.how do we calculate it?what is its formula?how can we know corresponding energy in kcal/mol for some other temperature say 70 degree Celsius.thanking you.kind regards and best wishesashutoshvaranasi India
John KellerGood luck!To estimate free energy of activation, you would need to optimize and do frequency calculation for the starting compound and transition state, and take the difference in free energies between these two. Locating the T.S. is sometimes difficult: if you are using Gaussian, the Opt=TS, or OPT=QST2, or Opt=QST3 methods are used.To a good approximation at moderate temperatures, the free energy of activation is not dependent on temperature. Reactions go faster at higher temperatures because a higher proportion of molecules have attained a kinetic energy greater or equal to the free energy of activation.Hi Ashutosh,You can use the Eyring-Polanyi equation to calculate k the unimolecular rate constant, given Gibbs Free Energy of Activation delGdoubledagger. Google "Eyring equation wiki" to see the equation written out.
On Thu, Apr 4, 2013 at 7:17 PM, ashutosh gupta ashu1809 a gmail.com <owner-chemistry]~[ccl.net> wrote:
Dear All,Normally it is assumed that if the activation barrier is less than 20 kcal/mol, then the reaction occurs at ROOM TEMPERATURE.how do we calculate it?what is its formula?how can we know corresponding energy in kcal/mol for some other temperature say 70 degree Celsius.thanking you.kind regards and best wishesashutoshvaranasi India
John KellerGood luck!To estimate free energy of activation, you would need to optimize and do frequency calculation for the starting compound and transition state, and take the difference in free energies between these two. Locating the T.S. is sometimes difficult: if you are using Gaussian, the Opt=TS, or OPT=QST2, or Opt=QST3 methods are used.To a good approximation at moderate temperatures, the free energy of activation is not dependent on temperature. Reactions go faster at higher temperatures because a higher proportion of molecules have attained a kinetic energy greater or equal to the free energy of activation.Hi Ashutosh,You can use the Eyring-Polanyi equation to calculate k the unimolecular rate constant, given Gibbs Free Energy of Activation delGdoubledagger. Google "Eyring equation wiki" to see the equation written out.
On Thu, Apr 4, 2013 at 7:17 PM, ashutosh gupta ashu1809 a gmail.com <owner-chemistry]~[ccl.net> wrote:
Dear All,Normally it is assumed that if the activation barrier is less than 20 kcal/mol, then the reaction occurs at ROOM TEMPERATURE.how do we calculate it?what is its formula?how can we know corresponding energy in kcal/mol for some other temperature say 70 degree Celsius.thanking you.kind regards and best wishesashutoshvaranasi India