Differentiating between Kinetics and Thermodynamically Controlled

[Susanna Givan 2B]

How do we differentiate if a reaction is a kinetics controlled versus when it is thermodynamically controlled?

[Adrienne Chan 1G]

Hey! So kinetics vs thermodynamically controlled depends on temperature. Kinetics controlled reactions are at lower temperatures, and thermodynamically controlled ones are at higher temperatures.

One example Lavelle gave during class was diamond turning into graphite. Normally, we don't see diamond turning into carbon even though graphite is more thermodynamically stable. This is due to the reaction being kinetically controlled at low temperatures, the activation energy for that reaction to occur is way, way beyond what we experience in daily life. But at high temperatures, the activation energy can be overcome, and diamond can turn into graphite spontaneously.

In addition, this website helped me out a lot for a second example: https://chem.libretexts.org/Courses/Athabasca_University/Chemistry_350%3A_Organic_Chemistry_I/14%3A_Conjugated_Compounds_and_Ultraviolet_Spectroscopy/14.03%3A_Kinetic_vs._Thermodynamic_Control_of_Reactions If you scroll down to the energy diagram, you will see a more complex reaction for thermodynamic vs kinetic control. The two products are called B and C. The product B has a lower activation energy to form it, so it will form faster, making the reaction kinetically controlled at lower temperatures. At high temperatures, C is the most thermodynamically stable molecule (due to it having the lowest energy) but a higher activation energy than B. This means that at high temperatures, C will be favored and the reaction will be thermodynamically controlled. Hope this helps!

[Kiara Phillips 3L]

I believe the main this is just about reading the questions, often they give you a hint or word something differently when asking you to use kinetics vs thermo. I would just practice solving both and you will pick up on the jargon. Hope this helps!