exam 6 question 12

[harrington5609]

I am confused..I thought that the more stable a molecule is, the less likely it is to react, which would call for a greater activation energy rather than a lower one. Am I confusing gen chem rules with the stability of the intermediate? Maybe what the explanation is saying is that the more stable the intermediate the more likely it is to react, so a lower activation energy is needed?

[admin]

The thermodynamic product has higher activation energy but a lower Gibbs free energy. The kinetic product has a lower activation energy yet has higher Gibbs free energy. Since the kinetic product requires a lower activation energy, it requires a lower temperature, in this case -80 degrees Celsius, also the kinetic product is formed faster. On the other hand, the thermodynamic product requires a higher activation energy, meaning a higher temperature of reaction, in this case 40 degrees Celsius.
Therefore, the answer and explanation are good. Moreover, the more stable “intermediate” formed (and not reactant) will favor its product formation via the kinetics due to a lower activation energy barrier to be surpassed. This is a test of both your knowledge base on kinetics and thermodynamics by incorporating temperature differences and thus different product formation due to the temperature differences.