A researcher studies the electrophilic addition of HBr to 1,3-butadiene
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
A researcher studies the electrophilic addition of HBr to 1,3-butadiene. At 0 °C, the reaction mixture contains 75 % of the 1,2-addition product and 25 % of the 1,4-addition product after 2 minutes. A separate experiment performed at 40 °C for the same amount of time produces 20 % of the 1,2-addition product and 80 % of the 1,4-addition product.
Answer the following questions about the observations described above.
(a) Describe what is meant by a reaction being under kinetic control versus thermodynamic control.
(b) Using the data provided, explain why the product distribution differs at 0 °C and 40 °C. In your explanation, discuss the relative activation energies and standard Gibbs free energies of formation for the two products.
(c) Predict qualitatively how the product distribution would change if the mixture obtained at 0 °C were warmed to 40 °C and left to stand for several hours before analysis. Justify your prediction.